Weekend Ash to Pottery Competition

Rauðibotn. Image from Icelandic Mag.

A couple of weeks ago we got an email from one of our readers who is currently studying how to make ceramics and porcelain in Iceland. She was wondering about what ashes might give the best colours.

I am not the best geologist around, and instead concentrate on the squiggly stuff on seismometers and bouncing dots from GPS-stations, I thought it might be a fun weekend challenge for our esteemed readers to help her out.

I have edited the emails and put them below. So, hope that you all will have fun!


A bowl of ash

Seyðishólar, picture taken by the person asking the questions.

In my work I examine local raw material not from a scientific point of view but more from aesthetic. I use them to colour ceramic objects.

For my diploma project I was interested in working with basaltic volcanic ashes as I suppose they are rich in iron (which gives me a colour).

As I know basically nothing or almost nothing about geology, I have problems with telling which material is which and where to find the material I could work with.

This is where I would need some help.

This weekend I went to Seyðishólar. I picked up some red pumice rocks, but the problem is that even if I grind it very well, I´m not able to get super fine powder.

This is when I stumbled upon your article and found the pictures of volcanic ash layers (which is called tephra I guess, from the article I read on your website).

I tried to find this kind of layer near Seyðishólar but the ground was frozen so I could pick anything up.


My questions

What I see in the picture below (the quarry in Seyðishólar) is not tephra right, or is it? If not, are those different lava rocks?

If I would like to find tephra layers, would you recommend looking for some open earth profile (possibly in Seyðishólar) or just try to dig a hole somewhere in this area? (Editor’s question: Or are there other better areas?)

And one more question about the method of recognizing the layers (just by curiosity). Are layers of tephra recognized by the order of volcanic eruptions and then also colours? Are there any other factors involved?


Points for answers

The absurd crater called Apple Crater. Sometimes nature uses Verner Panton as a colour consultant.

I will award points for good answers, good suggestions, and Editor’s Choice Award points for answers that are “out there, but helpful”. I will declare a winner at the end of the next article we publish.

Carl Rehnberg

416 thoughts on “Weekend Ash to Pottery Competition

  1. This would have all the colours I would need with the exception of blue. Hard to get there though. Other readers will have better proposals, but I can’t resist:

    Dallol, Ethipia

    • Those are salts, and I do not know how useful those would be for pottery.

      • Many will be microbial and thus useless.
        I think the blues are often/mostly very small silica(?) particles diffracting light (blue sky).
        For ceramics glazes are often made (I think) by melting glass alongside the colouring elements essentially to make a glass solution, then cooling and grinding very finely.
        For a lava glaze I would look for a rustic look.
        Grinding is either expensive or slow. The best way, if you have something brittle and not too hard, is to attack it with a hammer drill and collect the grindings. Another effective way is how stone eggs are made, by grinding with coarse carborundum (SiC) in a capped off rotating tube containing your rocks and some water. After a week open, wash out the fines and sieve to your requirements. The finest can be had by allowing ALL the liquid (including washings) to settle in a large glass jar/bucket for a week then carefully sucking (or spooning further down) each layer which will be separated by size and density.

        Then mix with glass powder/granules with the appropriate melting temperature you require.

        I suspect a glaze with big (~1mm) lumps may even be ‘artistic’ in texture.

        You will already know about reducing and oxidising firings.

        PS Excellent record keeping id required if you want to repeat something that was successful. You will not be happy if you cannot remember EXACTLY where you got it from.

        PPS I would test stuff on either pre-bought times (white) or make up some tablets of biscuit ware using the clay of your choice and see what different things do.

        PPPS I last did potting 50 years ago, but I find the chemistry interesting.

        PPPPS You can get your own elemental salts by dissolving assorted things about the house but note many are EXCEEDINGLY toxic as salts. Iron, nickle, copper, chromium, (avoid Cadmium) are all probably witin a few meters of you.

        • PPS I would test stuff on either pre-bought XXXX TILES not times (white) or make up some tablets of biscuit ware using the clay of your choice and see what different things do.

      • Lots of the transition metals do two or more colours depending on their oxidation states.
        Iron gives orange-reds and dark greens
        Chromium bright red or rich green
        Vanadium similar but a bit more bluish on the green
        Manganese pink or yellow green
        Copper deep red, green, blue
        Cobalt pink & dark blue
        I wonder how much controlling the 02 content to produce an oxidizing or reducing environment during the firing could have on the final colour.

        • A lot, and I’m unclear how its controlled commercially.
          It may well not be and elements chosen for their oxidised state (in air). With coal/straw/charcoal (even gas) firing it may be different but CO is toxic.
          The black and red in ancient greek pottery are two iron oxidation states.
          Also, how do you get high enough levels of elements other than iron yo be useful out of what is pretty well an island of basalt?

          • There are probably other factors involved too, in the case of iron, fully oxidized means the iron has enough oxygen to form hematite (which is red). Partially oxidized iron is magnetite, which is black. More reduction and the iron will bind to silica to give the greens.
            Now on to find useful concentrations of other materials, generally we get the elements to concentrate by adding water (hydrothermal activity), or sulphur which will scavenge things like copper, lead, zinc, nickel and cobalt from silicate magma. Chalcopyrite is the most common copper sulphide, and occurs frequently as an accessory but it also contains iron. It weathers easily, at the surface it will oxidize to the sulphate, which is soluble (and has a pretty blue colour). Might be able to turn this to advantage though. Firing will drive off any sulphur leaving the metals behind.

    • Salts will melt in the pottery furnace
      Not good at all .. melts at 800 C into a red glowing watery liquid

      • I guessed, I just love the pic, Jesper. Imagine we would only see black and white. We can be happy about our retina. Sometimes I think we became what we are just for the reason to admire earth. And space.

      • Remarkable sentence, Carl: “I am not the best geologist around”. I could say that about Biochemistry or Pharmacology today. I first thought boring and nearly ignored the piece. But as usual on VC it became interesting digging into it. Just saying: It doesn’t have a whole lot to do with Geology. More with Geothermal indeed, as plants for colours might grow more where it’s warm. But this I don’t know not knowing too much about plants of all sorts.
        It is bothersome to ggl for plants and only get power plants first, of all sorts. I helped myself with fauna and flora.

        • Geology is mainly knappology, ie remembering what are the properties of Mysterisite, Bullshiterite and Spankerite. My brain is not good at remembering those things.

          I am though pretty good at geophysics where I can derive things from general elementa of physics. My brain is not wired for memory, it is wired for brute force.

          For instance, I could never become an MD (I tried once), because I could not memorize a gazillion bones, nerves and assorted whatnots. I deeply respect my wife who I can wake up in the middle of the night and have her recite the entire human anatomy flawlessly (edeitic memory).

          • I did 95% in anatomy. Better at memory, but not longterm. It gets lost. It sticks for a few years, and if it should stay in your brain for a longer period you either have to work with it or memorize it. You tried to become a doctor? I imagine surgeon.

          • Your wife might have told you this, if yes it is a repetion: There is one bone concerning brute force which you have to keep an eye on: The Scaphoid. It is a root bone of the hand, situated at the base of the thumb. When you overstretch the thumb you get a little concave indentation at the base on the back of your hand. The scaphoid is underneath. When you exert pressure in the dent (also called tabatière for obvious reasons) and it is painful it might be fractured. This might seem insignificant, but it is not. If not diagnosed (only MRI) and treated right away it can produce an aseptic necrosis which later leads to arthrosis.
            The other way to get it is ice-scating or skiing or other sports and falling on it with some “brute force”. Useful to know.

          • The other group who used to get it were the workers with the pneumatic hammers, possibly good to know. They got it with time, the permanent pressure and shaking was just as bad. They used to get two to three occupational diseases, deafness, scaphoid fracture and sometimes dust lungs. That’s why protective gear became obligatory, also on airports. Protective gear is also very important for builders when they take down an older building with asbestos and for farmers (farmers lung, an alveolitis). So, it’s not only volcanoes.

          • Have a go at contemporary molecular biology and genetics. You’d likely prefer having rocks in your head.

  2. I should have clarified, it must be Icelandic ash, tephra, and whatnot… 🙂

  3. Most clays in Iceland are dark and basaltic, meaning the pots will be dark glossy coloured, althrough adding sillica rich ryholite clays and iron oxide rich clays coud add some color.

    If you fire them to almost 1200 C you will get that nice glassy porcelain look, althrough pots of more sillica rich continetal clays.. coud perhaps be fired to much higher temperatures

  4. I’m into blue and blue and white. I think volcanoes are excluded here. Blue was won from plants (Indigo), today synthetic, and from Cobalt (Smalt). Royal Copenhagen worked (and probably still works) with Smalt or Cobalt, but even the Romans and the Ming Dynasty used it.
    I’m out. Blue sky.

    • Cobalt glass are indeed so beautyful!
      Reminds me of the clear blue waters of Hawaii and Azores

      Very beautful indeed!

    • hauyne has a volcanic origin. It is the blue in the Girl with the Pearl Earring

        • I’m not sure what would happen if you mixed these minerals with glass and melted them. I would expect different and less interesting coloured minerals to result.
          There is good reason why most (?all) pottery glazes are based on elements. Some are quite astonishing, such as a colloidal gold in colouring some red glasses.

  5. A woman from our rock club would take the tailings from the grinders and put them into her flower beds. She produced some of the most amazingly colored Dahlias. She would bring them to the meetings and they would be included as raffle prizes. Sorry FarmerOZ, not very scientific, but chaotic results are sometimes gratifying.

    • I would think the black/yellow/brown colours are various oxidative states of iton. With luck there will be some manganese present (can do various shades, often blue and purple depending. One thing I didn’t mention is that things like cobalt can look nearly black is in high concentration so some rather ‘dilute’ (with glass powder) tests should also be made.

    • Does not look very colorful for me
      Is it just the ligthing at that time of the photo ?

  6. Key sentence: “I´m not able to get super fine powder.”
    So, I suggest a beach. One of the most famous in Iceland is Reynisfjara. It is black sand though. Does she want to make black pottery? Why not – black pottery is in. Villeroy and Boch have black dishes and probably also other companies.


    Other volcanic beaches (need to grind though, but huge colour selection):

    • Decades ago we were on a very isolated cornish beach and round the headland came a middle aged man
      carrying what was clearly a heavy bucket. He was an ex-miner who now made a living panning tin off the beaches. He said if you knew what you were looking at you could find areas of the beach very high is selected elements separated by wind and wave. He had 1/2 steel bucket containing (I would guess) 20kg of nearly pure tin sulphide. So perhaps picking out areas of beach that look like they might have done something similar might be a goer?
      PS Sadly many metallic compounds in their raw state tend to black-brown.

      • Beaches are happy hunting grounds. About 30 years ago I talked with a master potter on Cape Cod, Massachusetts. He used to walk the beaches at low tide and find a coarse black sand. He incorporated a handful of this into his clay or glaze mix for a speckled pattern.

  7. So the rules are Icelandic “ash to pottery”. Nothing says volcanic. Try firing with Icelandic wool or Icelandic horse hair and see what colors you get!

    • Yeah, it’s overwhelming, isn’t it. Use ash to make colour instead of buying some minerals. Then burn the ash on a plate again in an oven. When I tried to make colour once (futile) at least I tried plants. We can all try it, if we have an oven. The first problem will be to bind it. After some fun with colourful landscapes I pondered whether it is April 1st. That’s why I came along with mud. Clay is also possible. Then Carl came around the corner with Tephra of all things.
      The next problem is whether it’s allowed to take tephra out, it is such a fine ggl earth and fauna and flora, but it might be possible in some insignificant places, and on beaches nobody would mind. I just cannot imagine that it binds at all, let alone burn again. But I am not a master in colour blending. I tried Stucco Veneziano once. It was a complete desastre, and I had to hide it behind a wall-paper, but as I said, this is out of my capabilities. I’m glad when my cake goes up to the right size.
      So others have to figure this out.

      • What’s overwhelming too is the fact that it likes to float when on water, so how mix it with water.
        We’ll see. Somebody will tell. I have a recipe for that though. Take Crème fraîche and then as must chili as you feel is right, and you sure get a wonderful volcanic colour (lava). With some flour this will turn into a nice plaster. Buy the chili on the market in Reykjavik, and then it is an Icelandic volcanic product. Works for food and drinks as well: the more chili, the more volcano in the throat.
        Nature pottery, found with this game:

        Source: Reddit, “Cumbre Vieja: Circular figures in the tephra caused by wind erosion (see links and comments for more details)”

        Getting around with ash.

        • Mmm . . . looks like a giant cinnamon roll, big enough to share with everybody!

  8. Not sure how colourful Iceland is. Basalt is black, but can weather red. Olivine is green, if you can find it in high. enough proportions (like the green beach in Hawaii).

    Colour comes from mineral and they may be added to the lava much later, mainly in hydrothermal areas. Is there colour in Askja? Sulphur adds a touch of yellow. Kerlingarfjöl is hydrothermal and colourful but is more rhyolitic.

    If you want the entire colour palette: it is not volcanic (I think) but rainbow mountain in China is incredible (not been there so can only point at pictures). There is a similar mountain in Peru.

    Obviously the colours are enhanced but natural colour photos also look very impressive

    • When I read about the coloured mountain in Peru I also had to read a passage about a fight for mining concessions. It is absolutely unbelievable that people exist who want to mine there. But that’s the way it is. These people if they have permission will destroy the earth in a time span of 100 – 500 years. Not million. No, 0,1 – 0,5 k.

      Rainbow Mountain, Peru:

    • Sorry, maybe it is the same area. I thought the pic was from China.

      • Worlds apart – one is from Peru, the other from China. The Chinese rainbow mountains are a protected area, you’ll be happy to know. And will remain protected as long as the tourists keep coming, I expect.

        • Always looking for connections when seeing similarities I found this:

          This goes for China’s painted mountains (mid Cretacious), but Peru’s are supposed to be younger. On the other hand they haven’t even been known that long in Peru, so not too much research I guess. But in any case, whether Nazca or Farallon they are both probably caused by subduction and erosion.

          It would be funny though if it were the two old plates on both sides.
          In any case nothing is ever lost, just metamorphized, Ovid saw it first.

  9. Dimmuborgir in Iceland. Hopefully the image shows up.

    [It didn’t – admin]

        • This is from Wikimedia. On Flickr, it somehow doesn’t work when it comes to copying photo link.

          • Wikimedia-Commons, best with source like you dido.
            Flickr, Alamy: Own it, pay people for it. I don’t know whether that works. Last but not least there are many people who can do brillant photographs themselves. So, who buys the staff? Big companies for their entrance hall I guess. Big bluff everything.

  10. Hmmm icelandic colourful clays.. Probably some rhyolitic place – since Landmannalaugar was already mentioned in a way I would go for Kerlingarfjöll – an absolutely stunning area with lots of volcanic features to explore. Found lava tubes, fields, maars, hot springs, geysers etc etc. And plenty of colourful stones/clays/fumaroles with small blue glaciers behind, paradise for any photographer!

  11. I guess it would be easy to make red-brown clay from all the iron in the basalt, but that is really about it in 99% of iceland I think. Maybe if rhyolite clay was used in alternation with basalt clay, that could give a nice contrast of white and dark red. But really, to get more colours you need other transition metals and such, their oxides in the ores. Iceland, or Hawaii, or really any basaltic island, that wont exist yet because those metals need millions of years to get dissolved and precipitated out into the ore deposits. I guess carl would know a lot more about that though, maybe there is some copper or nickel in Iceland. Those would give a nice blue and green colour.

    My assumptions:

    Weathered basalt – deep red/brown
    Fresh basalt – probably black, or black specks
    Rhyolite – white or pink
    Andesite – maybe steel grey?
    I dont know if the colours of the rock as a bulk item will actually show if the rock is powdered and added to clay. And pottery clay is already iron rich anyway.
    I also know that the only convenient source of andesite in Iceland would be at Hekla, and Carl will not want to go there 😉 Most andesite looks the same as basalt anyway.

    Iceland has got sort of the same problem as Hawaii in this regard, there are colourful places but they are not made from rocks, rather salts and sulfur precipitated from fumaroles, not refractory compounds that can go into pottery. Sort of limits the options a bit.

    Does Iceland have an olivine sand beach like Papakolea in Hawaii? Reykjanes has got a lot of picrite lava. Olivine might look very nice in pottery.

  12. I’m not a geoscientist, just a biologist with an interest in pottery, in which I have dabbled at various times.

    It is indeed fun to collect and use raw materials in pottery. The main problem is finding a source where there is enough fine grained material
    that can be cleaned up using a fine meshed sieve. Coarse grained materials that contain air pockets can pop/explode in the kiln and cause damage.
    Unfortunately I know nothing of Iceland’s geology other than what I’ve read on this site. What you need are ash deposits that can be easily ground
    into a fine powder. If there exists an analysis of the oxide makeup of this ash then you can make reasonable estimates whether any other materials
    need to be added to arrive a mixture that will melt at a suitable firing temperature and have acceptable coefficient of expansion to prevent cracking
    on post-melt cooling (see last sentence for useful reference).

    The colour of a material doesn’t necessarily predict the colour after firing. I had a blue-gray clay that fired up yellow ochre.

    Also firing with or without oxygen can have remarkable effects on the colours. For example, copper oxide/carbonate is used in Raku
    pottery and can give an amazing spectrum of colours with post-melt reduction (just google “raku pottery” and go to images).

    Finally, for those that wish to dig into ceramic materials and their chemical and physical properties there is a great online reference at “Digital Fire”.

    [This was held for approval, as happens to all first-time comments (and regrettably necessary). Future comments should appear instantly – Admin]

  13. Based on two rather dubious things; me making some pottery (just a couple of pieces, which ended up looking awful) in art class in high school, and my interest in history (which means that, almost as long ago, I liked looking at old newspapers) I can say that after the 1980 St Helens eruption, it was in the news of the time that some potters in the area (such as Spokane) where there was ashfall were saving barrels of it for glaze (and I’m assuming this was for base glaze). I’ve seen (Just a few years ago) souvenir pottery in tourist shops near St Helens claiming to be made from this ash. The colors vary a lot, so I think they must be adding colorants to most of it. (and that ash wasn’t basaltic).

    So, from this, I think we can say that St Helens ash, at least, made a workable glaze base. But for colors… problematic, because glaze colorants are often nothing like their finished form as raw materiel. I remember working with blue colorant (cobalt and some other metals, I think) that was not at all blue until the pottery was fired. So, what you start with is likely not going to be the color you get.

    So, you really need to consider that the glaze base and the colorant may be two different things. My suggestion regards colors is to look at what potters actually use to get certain colors, and look for ash rich in what produces the colorants that you seek. However, don’t assume (because you will be wrong in most cases) that the in-situ color of the ash will look anything like what it does for a glaze.

    A quick internet search yielded this, which I think may be helpful.

    As for tephra layers and what colors they make… I’m guessing that one way is find a chemical analysis and see how it stacks up as a glaze colorant, and another would be to ask local potters. Another is advice above from Farmeroz; try samples and see what happens. The iron content is something to bear in mind; iron oxides are often used in glazes, but if you’re after the oxide’s color, beware that the kiln temp does not exceed the temp that the oxide breaks down at.

    For fine grinding, I think you’re going to need a ball mill.

  14. Long time lurker and avid follower of all things Geoscience. Very much of a fan of the reasoned dialogs and careful speculation.
    What a fun post and here is a thing I can contribute as Ceramics and Glass are areas of avid interest.
    If I went looking for materials for making ceramics, the fine clays of the Mud Pots would be number one on the list. In general Clays are fine enough to withstand a thing called ‘The Ceramic Change’ and become the glassy substance we call ceramics. Thats just the first step though and creates the Bisque. Creating glazes with the clays and added chemicals is where the fun starts by mixing the finest clays with various elements. Like Iron, Cobalt, Ash, etc. into a self-formulated glaze. Thats where the beautiful colors come from. Ash by itself and a few other chemicals makes beautiful Glass items and I have some blown ornaments made from Ash from Mt. St. Helens.

    [This was held for approval, as happens to all first-time comments (and regrettably necessary). Future comments should appear instantly – Admin]

  15. Actually, the more I think about it, rhyolite clay might just turn into obsidian in a kiln, so actually jet black not white. Probably also not a good material for pottery either, it isnt very strong.

  16. https://i.imgur.com/Bd3ZxB8.mp4

    Kilauea really going quite strong with these eruption episodes now, most of the caldera floor was covered this time. I think it has gone somewhat beyond a lava lake filling up with some gas vents on the crust, this looks to be much more like actual shield building, the filling becoming mostly through surface activity.

    In 10 years we might well have a large shield at Halemaumau instead of a caldera, actually at the rate of filling now it could be much less than 10 years even, the long term supply seems to have gone up since the start of the year. The ERZ also seems quiet, the conduit is only open to Mauna Ulu because it goes at angle to the south flank movement, within the rift it can probably only stay open under pressure which is not there currently. So the Pu’u O’o stations now only show south flank movement.
    My guess is we have just entered Observatory shield V2.0, and that the shield is going to fill the whole caldera over the next 10-15 years. Then we will see flows advancing southwest, first as a’a flows, short lived but fast, and eventually as sustained pahoehoe flows that will reach the ocean. Shields or fountaining vents might also form south of Halemaumau, at Keanakako’i and at Kilauea Iki afterwards or at the same time, where other separate magma chambers exist within the summit structure. With any luck the action is all directed south, so that the north rim of the caldera is never overtopped.

    • Maybe just to give sense of scale, this is the entire lava field of Fagradalshraun overlayed to Kilauea. Really shows how massive Kilauea really is, the current eruption is contained inside a caldera but these flows are probably of comparable intensity.

      • Fagra-unspellable’s lava flows are actually larger than I’d expected when seen like this. Thanks, Chad.

        • Yes, not big not small. But if 150 million m3 of lava actually erupted in Kilaueas caldera it would barely fill it any more than the actual lake there now does 🙂

          I also expect the flow would have been a lot more extensive if not for filling in several valleys, these sorts of fluid lava flows are very mobile and can flow a long way very easily.

      • And Kilaueas submarine massive is 200 kilometers long 🙂

  17. Interesting effects can come from multilayered silicate minerals. Even fired, if there isn’t too much flux material, the silicates will stay pretty much intact, producing rainbow effects due to thin-film diffraction. I’m not sure how many of these are in Iceland, but I’m thinking micas, opals, or (probably not as well) bio-generated silicates like abalone. There are also some places where basaltic glass has been weathered into similar structures. I know there’s been some found in some freshwater bodies on Iceland, but I forget where.

    Good luck, and you must return with pictures both of the successes and failures! This is a very cool idea!

    • Thank you! That is very good information. So the air pressure wave was measured at more than 10mbar, indeed more than enough to make ears pop.

    • Thanks Diedre!

      That’s a superb video, but what stunned me was the pressure DROP before the shockwaves hit. There was considerable delay as well, several seconds.

      What are the physics here? Why would the pressure drop before the shockwave hit? A shockwave is essentially a pressure front moving at the local speed of sound, so I can’t figure out why pressure would drop. I’m aware that tsumais sometimes cause the shore water to receded before the wave arrives, but I think that’s a surface effect.

      Anyone know why this occurred? The only mechanism I can even guess at (because the negative pressure effect would, defacto, have to travel faster than sound) would be a sort of surface effect, a massive amount of air shoved upward at the eruption site. If so, most of the energy from the blasts is directed upwards. Just a guess.

    • I watched this before, and I am still unclear whether the long wave pressure peak is best linked with the sharp crack following or perhaps the earlier one. Offhand I would expect the sharp crack to lead the long slow, although I cannot say why I think this.

      • Note how the clouds in the sky are being sucked toward the eruption for a while, before the normal upper winds resume. This suggests that the eruption caused a large low pressure zone, no doubt related to the rising column. The bangs are shock waves. They would have traveled at higher altitude where the sound speed is slower, by some 10%. Over 70 km distance that means the shock wave would arrive some 20-30 second after the pressure wave. Note that there is rumbling audible some seconds before the bang. That shows that the sound has a spread of travel times. I don’t know whether that is because the explosion was so large (five second would be almost 2 kilometers) or because it traveled at a range of speeds. But when he says that the pressure drop preceeds the bang, the time difference is much larger. He waits 15 seconds and that was not enough, so perhaps 30seconds. (I don’t doubt his claim that the waves and the bangs are related.) That would be the difference between the speed of sound at sea level, and that at 10 kilometer altitude.

        • Hrmmm.

          The dynamic I have in mind (And I might be very wrong) can be visualized with a plate in a sink half full of water. Hold the plate flat a few inches under the surface, then lift it quickly out of the water. The water level around it will drop due to the uplift under the plate – a low pressure area.

          I’m thinking that Hunga Tonga did that to the local atmosphere (hence, the cloud motion you mentioned). I’m also thinking that the reason we had multiple shockwaves was both what you say (differing arrival times due to differing speeds of sound), and IMHO there was more than one blast – there were several.

          There was an odd effect when St Helens blew in 1980; the blast was heard hundreds of miles away, but it was not heard close to (less than about 40 miles) to the volcano. They call this “The Zone of Silence”. That’s puzzled me for years (I learned of it while visiting St. Helens), and recently I found a study (from Sandia National Laboratories) that, I think, explains it well. and may also help us understand what happened on a much larger scale at Hunga Tonga. (It supports your theory regarding the differing speed of sound, plus gets into refraction from the stratosphere)

  18. Suggestion from a materials scientist.
    Be REALLY nice to the mat. sci. department at your University and they may let you use their ball milling instruments.
    Ball milling will yield really fine powder which should be easy to incorporate in your ceramics. Drawbacks: the process is slow and has a low throughput, at least for benchtop instruments. Also, it may induce some compositional changes and change the colors.
    It is worth a try, though.
    I can help you maybe a bit more, let me know.
    Other folks, feel free to say that this idea is boneheaded, it would not be the first time, nor the last.

  19. Read up a bit on the first picture of Rauðibotn (beauty) and saw – known of course to all who have more experience with Iceland – that it belongs to Eldgja. Found this piece by Albert:

    and some additional information:
    “Rauðibotn is part of the Eldgjá craters, a chain of volcanic craters which stretches through the Central Highlands from Mýrdalsjökull glacier to Vatnajökull glacier. Eldgjá is connected to the monster volcano Katla, as both are part of the same volcanic system. Eldgjá has only erupted once since the Viking settlement of Iceland in the 9th century: In 934 a massive eruption, believed to be the largest volcanic eruption to take place in Iceland in the past millennia.
    The 934 eruption produced a lava field which covers approximately 800 square kilometers (310 square miles), 18 cubic kilometers (4.3 cubic miles) of lava and 5-7 cubic kilometers (1.2-1.7 cubic miles) of tephra and ash. The size of the lava field is large enough to cover all of New York City, and then some. The impact of the eruption on global weather systems was catastrophic, causing crop failures and hunger in Europe. Temperatures all over the Northern Hemisphere dropped, causing rivers as far as present day Iran to have frozen over.

    The giant eruption is believed to have inspired the descriptions of Ragnarrök in Völuspá”.

    “Darkness comes there
    dragon flying,
    down from, below
    The bodies of men
    on her wings she bears,
    Niðhöggr to get,
    now she will land.”
    Völuspá, final stanza

    From “The End of the World”, Carl:

    So I think, aside from all colour and nice pottery, it would be kind of nice if Eldgja with Rauðibotn didn’t erupt again for the time being.

    • Yes, it was part of the main vent of Eldgja, and is where the tallest fountains were too. Eldgja was not exactly like Laki, it was at first an eccentric conduit from the deeper plumbing of Katla, which erupted as a radial fissure. This was the source of most tephra (subglacial eruptions) and the biggest lava flow. There was a similar eruption around 7000 years ago, which also made a large flow field, and was erupted from eccentric radial vents. Katla is not really a rift volcano on its own.
      Eldgja was though close enough to the rift zone that a dike was able to move that way, eventually 70 km north deep into the fissure swarm of Grimsvotn. Who knows, if it had stayed as a radial fracture it could have been even bigger in volume, because the dike would have taken a lot away, it could have been Icelands biggest Holocene eruption period. The dike probably was at least 10 meters wide and 10 km deep, so maybe another 10 km3 of magma. It might well have been much wider too given the scale of rifting and intensity of the eruptions along the dike.

      Really Eldgja was kind of a freak event, no wonder Katla is still crippled over 1000 years later. Im also not sure if it should be included in the normal rift cycle of the area, things were really shaken up afterwards. Vatnafjoll went dormant, Veidivotn went from 250 year eruption intervals to 500-600 year intervals, and Hekla has erupted much more. Not to mention Laki, which was another eruption much bigger than normal and from a system not typical for that sort of activity, only 800 years later. It is almost like Eldgja broke up the plate, so instead of a narrow band from Bardarbunga southwestwards it was much more broad, and covering several other systems.

  20. Very interresting subject. Paint and colours was my profession for a few years many years ago, but on the volcanic side of this I am fairly blank. But I do have a very dear friend here in the island of Chios, Greece who is an amazing artist, ceramist who does the most incredible things colouring his own handmade pieces for a living. Truely a rare spirit in todays modern fast-lane time. We had a nice lunch here at our house friday, so had the Carl’s piece been out before I would have been able to forward at least something on the subject.

    I did message him today, so maybe he will write something here or to me to forward on this interresting subject. He has a ceramic art studio in Mesta, Chios and below is some information if it should be of any interrest. Will post again if I know something more. I know he just started this years work/creative process. I guess some things are “trade secrets” in the area of colouring, but the basics on how to find and source the best raw materials would be part of his world. Thuth be told my focus has been on the art itself. Which we really enjoy.

    Enjoy: https://toultouline.com/2019/09/30/nikos-balatsos-ceramics-artist-in-mesta-chios-greece/


    • I messaged with him and this is actually not his area of expertice either actually. When I think of it it makes sense. He uses very high quality materials that needs to work well together. To experiment with costly materials can be a risky undertaking when there already are so many things that can (and do) go wrong during the artistic process and the several stages of burning that is required through the way he works.

      There are so many techniques involved I will not even begin. And I know too little. The key for him is to have very good raw materials to some degree easing his work and by doing so at least weeding out some obvious difficult part of the whole process of making ceramic art.

      From that you could derive that you have to trust the quality of the materials you want to use, and that you either have to trail and error to achieve that, or have samples analyzed to go forward with pure volcanic material for colouring. It IS the basis of a vast range of old colouring techniques and thus absolutely possible, but how to make sure of purety (many “pollutants” like salt or sulphurs could destroy or damage the intended result) to have the wanted result.

      In the vast area of natural colouring the site linked to below has a lot of information of historical uses, and in the area of colouring ceramics oxides and minerals are what you need due to the nature of the process undergoing several burnings. Oxides are what he mostly uses to colour the clay. But again, to grind it fine enough and to know what exactly you have at hand would be step one and two. Sorry I could not be to more help, if any. But I am pretty sure there must be a geologist with an overly keen interrest in the area of colours (oxides) somewhere.


      Of course there are (natural) pigments derived from other sources (plants, three, tar, fish aso) but all colours suitable for colouring and glazing of ceramics are based on “chemistry” naturally occouring in the mineral-kingdom. And then again a lot found in or around volcanoes. Lapis Lazuli, manganese oxide, iron oxide, cobalt and zinc oxide just to mention a few colours. For the glacing silaca (oxide) is the key component with usually aluminium oxide as one (of more) agents.

      See the steps here; https://www.thesprucecrafts.com/what-goes-into-glazes-2746232

      Happy Tephra-hunt!

  21. Ash, after all, old art:
    “Ash glazing began around 1500 BC, in China during the Shang Dynasty, initially by accident as ash from the burnt wood in the kiln landed on pots. Around 1000 BC, the Chinese apparently realized that the ash covering the pieces was causing the glaze so they started adding the ash as a glaze before the pot went into the kiln. Ash glaze was the first glaze used in East Asia, and contained only ash, clay, and water.”

    Ash glaze, Japan, 18th century, same site

    • How did I get there?
      1. The post of Atle D took me right away to Thera/Santorini, of course. But the Minoans didn’t glaze.
      3. There was ash glaze though, mentioned in piece, but in the Far East and Persia/Iran.

      Minoan art: Clay, unglazed:

      Early Minoan Pottery, 3000-2600 BC, unglazed


      Minoan art is also made today as copies from original pieces in the museums of Crete and Santorini.

      • So when I see this it might be best to study as much of the old art as possible, make a form from clay from a mud-hole, colour it with plants from a volcano and glaze it with ash from some branches of a bush growing on the volcano.
        It would be totally volcanic, just not with tephra. I don’t know whether tephra would work as it would melt in her oven for ceramics (those work with high temperature indeed). But the antique glazers didn’t use molten rock but real ash, obviously. Tephra is not only ash. If she wants volcanic ash she might find it somewhere around Eyjafjallajökull. But I think after what I read it would only be good for the glazing.

        eyja, picture from wikimedia

      • That’s very clever, they have given it a grain, like wood.
        I think it inscribed for the colour change though.

  22. Concerning Iceland’s colours one more:


    • Seydisholar is mid-holocene, and is weathered lava and scoria. Listed as iron-rich basalt. It is probably too old to find much from digging.

    • Nice post. Poem at the end -“Dust if you must” (Rose Milligan). Fitting.

  23. Perhaps a bit more relevant to volcanoes, the chemistry of stained glass colors:


    Still see the usual suspects: cobalt. copper, chromium, cadmium.

    • As a colourant the Neodymium is a bit weird owing to it’s dichromatism. If held up to a light source the transmitted light is red, but reflected light is blue, just not easy to photograph.

      • I rather like the neodymium purple.

        These mineral pigments are in oil paints, sometimes makeup, and I guess for stained glass making.

    • Thank you so much for commenting!
      Those colors look absolutely amazing!
      I best like cobalt and manganese. Maybe add selenium-cadmium too. These 3 truly make colors I really haven’t seen before, at least not with glass.

    • Maybe someone can enlighten me a little in this regard:
      Are pretty much the oxidation states of a particular element governing the color of the glass?
      Or is it much more the element itself and a particular oxidation state (e.g. cobalt’s 2+) is used only since all others do exhibit poor color quality?
      – Why is 2+ cobalt used, when hypothetically(!) tungsten 3+ (don’t even know if that would be possible) would exhibit the same color?
      – Why can’t one obtain multiple colors from one single element provided it allows for different oxidation states (e.g. Fe 1+, Fe 2+, Fe 3+)? So you could hypothetically have turquoise, yellow and orange all from one element…

      There’s got to be practical constraints too, doesn’t it? Like whether you can get the element remain in the desired oxidation state when heating the glass mixture to melt it?

  24. After reading about the lupine war yesterday which is mainly lupines vs. berries by Egill Bjarnason (very good article I can recommend),

    I saw a second article there about puffins for dinner:

    I was just wondering whether it was ever tried to settle them on Kerguelen or Tristan da Cunha (a bit warmer than Kerguelen) to save them from Scandinavian pots. They chase them because father has chased them too. So I hope father didn’t read so they don’t read this. But the habit seems outdated.
    The article about lupines is nicer.

  25. Time for me to go a bit volcanic.
    I ended up at my favourite volcano to dislike, Hekla.

    It is a weird chemical reactor on its own.
    It has produced the world purest feldspar (good for porcelain production), it has also produced fluorfeldspar (flussing agent and binder). It is being excavated commercially, I have samples of it that stinks so bad of fluorine that I had to air it outside for 2 years before I could bring it inside.

    In that you have the piece of resistance, Heklaite.
    I do think that would be perfect for transparent glassy coating.

    Now to milling… I have as some of you know a bit of background in mining.
    I suggest running the host rock in a ball mill. Then roasting it to get rid of sulphur and fluorides. By experimenting with temperatures you can pinpoint what to remove.
    Even at low level roasting leaving most organic chemicals in you will increase the brittle coeficient. Then you run it again in a ball mill and sieve it.

    Now for the fun part. With a sturdy magnet you can remove unwanted magnetic parts such as iron (if you wish to do that), and you can also wash it with acids to purify it…

    Much fun to be had.

    • As usual you collect the prize yourself. Probably beers.
      I had fun which is a good prize as well. I hope all the others had fun as well.
      We just didn’t want to send her to Hekla. I avoided it.

    • Now the contesting (no prize without contesting): It was about colour.

      • Most people say that white is a colour, it is obviously though not.

        But, since everyone I had done colours I felt that it would be good to go for the base of things.

        But, if you mix Heklaite with Peridot you would get a very pale green or green-yellow colour. At least I believe so.

        • To be fair to you and Hekla: It is debated.
          “Newton showed just the opposite was true: light is composed of different spectral hues (he describes seven — red, orange, yellow, green, blue, indigo and violet), and all colours, including white, are formed by various mixtures of these hues.”
          “Some consider white to be a color, because white light comprises all hues on the visible light spectrum. And many do consider black to be a color, because you combine other pigments to create it on paper. But in a technical sense, black and white are not colors, they’re shades.”
          From “Understanding Black and White”, adobe dot com

          Black is basically not debated (no colour) as black doesn’t react with light.
          Light is the most important. In a cloudy moonless night there are only shades.
          All the beautiful colourful pictures from Iceland, China (Albert) and Peru are made on sunny days. Ocean pics need at least partly cloudy sky with some sun.

    • Btw, you might be a decent CEO. Points evenly distributed for the team, and at the end you come out with a solution. You might be pretty much aware of the worth of a team and a bit of Caesar:
      Primus inter pares.

      • Build a team, lead from the front.

        I have so far not been fired as a CEO to often… 😉
        Hard to be fired from your own companies though, at least as long as you do not mix prescription drugs with red wine, and then Tweet about how magical it makes you feel.
        (Okay, I will try to be nice now 🙂 )

    • How radioactive is it if there is elemental fluorine in the sample in high enough concentration to be irritating? That is quite the sample you have got there Carl.

      I think it should be said in normal circumstances if there is ever mention of fluorine in volcanic gas it is talking about HF and not elemental fluorine, there is a big difference. The elemental stuff basically cant exist as a bulk material in nature. It can exist in places where natural fluoride minerals have got elevated uranium concentration, where radioactive decay can break the chemical bonds, hence the above question.

      Elemental fluorine is basically what the air in hell is made of…

        • Ah, you meant HF not F2 (which would be unlikely to come from rock its so incredibly reactive).

          • Actually if there is a natural uranium found inside fluorite the radioactive decay can break the crystal structure and form free elemental fluorine. It cant recombine because the only thing with electrons available are other fluorine ions, no net energy transfer. I guess it must be able to move through the crystal lattice to not recombine with whatever it was originally stuck to.

            But I see now Carl was also talking about HF from the start. Why does Hekla have so much HF? The basalt vents on its fissure swarm presumably represent its deep source, and those are not elevated, nor are Katla or any other volcano in the SIVZ. And the rest of Iceland is low in halogens and high in sulfur just like Hawaii or any other basaltic island. Hekla must be getting its fluorine from a source within the crust that is presumably quite concentrated and very limited extent.

        • I once read that you can in fact encounter traces of pure F2 enclosed into fluorspar.
          If you really had some pure F2, Carl, what does it smell like?
          Would be intriguing to know 🙂

          • It have a very peculiar smell that is mineral and metalic, a bit like pouring pure chlorine on copper. Kind of like that fluor stuff that dentists use, but without the menthol.
            In Sweden when I was a kid they had us gargle with fluorine once every two weeks, that fluor was without any flavour additives, and had the same smell.

            It is very pervasive, if you have ever smelled it you will never forget it.

            In other words, I am trying to save that HF smells like HF, it is not like anything else.

  26. Some more colour:

    Antelope Canyon, Arizona, wikimedia commons:

    Fly Geysir, Nevada (hole man-made, formation geothermal):

    So light, water and erosion are the festive gown of earth.

    • And then what we basically gorgot, all of us, is algae:

      Lake Hiller, Middle Island, West Australia:

      Algae called Dunaliella Salina, Fleur de Sel:

      Both wikimedia commons.

      This gives me some extra thoughts about the pink terraces.

    • That looked oddly enough like the tequila fountain at my wedding…

    • Looks very dull on these Photos
      Something is wrong with my vison?

      After all I stared at the sun as a small child

      • Charme offensive today?
        Second photo from wikimedia I posted you consider dull, first was from Iceland.

      • Well I probaly haves permanent eye damage ..but The Fundus eye bottom photography have shown nothing on the macula

        But I have not done an OCT scan of the retina yet

        But Cobalt Glass is Indeed amazingly blue

      • Didn’t you say that North Sweden is dull too?

        Stora Sjöfallet National Park
        I don’t think that’s dull.

        • I may have probaly seriuos eye injury, yes its beautyful buty perhaps not very saturated in color. I haves to check my retinas:very likely coud be serious damage in the rpe layer

          But the cobalt glass you showed looked amazingly blue

          Fundus photography shown nothing in my eyes, althrough that is a very unrealible tool, Im going to check with OCT for a more defentive answer on my tougths on my eye health

          • I didn’t know there was a connection. In between I’ve been reading a paper about it. It can be on the red-green axis or on the blue-yellow axis. You might have it more on the read-green axis. Is this colourful for you? (It is an early painting by Vassily Kandinski when he was still in Russia, Riding Pair, in Museum Lenbachhaus in Munich):

            Thank God it is on wikimedia commons. I was looking for s.th. by Marc Chagall who also used beautiful blues. Did also pottery in his later years. He was living in the same village as Pablo Picasso who did pottery as well. St. Paul-de-Vence near Nizza, and they are said to have had their grandsons spying into each other studio to see what the other one was working on. So if you love blue you should look at their paintings. Chagall also did stained glass windows, and Picasso had a Blue Period the guitarrist being an example.

          • I found s.th. by Chagall by going to Reims Cathedral. Hope you can see and appreciate all of them:

            And I can add one by Franz Marc, German painter, 20th century:

            Hope you have more fun with the colours of those four painters.

          • Albert also mentioned Johannes Vermeer. He has beautiful blues.
            This is also nice: A Sapphire

            And then this is interesting for Volcano-specialists and geologists:

            “It is thought that blue diamonds, unlike most other diamonds, are formed in the lower part of Earth’s mantle, and that the boron creating their blue color originates from serpentinite carried down to the mantle by subducting ocean tectonic plates.”

            The most famous one seems to be “The Heart of Eternity”, found in South Africa. I assume that the Titanic (Cameron’s movie) was based on that.
            I think the end was silly. I wouldn’t have thrown this into the ocean. I’m still furious about the end.

    • Beautiful.
      This was an important post for me concerning Iceland as I saw more facettes than just tephra and lava and ice.
      Although Abert’s Greenland trilogy was very interesting I shuddered all the time.
      Maybe somebody can photoshop a sheep on that beach.

      • Yep, read that too.
        That was a hefty piece, if you imagine 😮

        • Forgot to add that I was referring to the Greenland trilogy.

  27. That Apple Crater looks interesting. According to reddit and other sources it is called “Rauðaskál”, and belongs to the Hekla system.

    Regarding pottery and clay/ceramics, I don’t know much, except that I’m currently using a clay flower pot (known as “Terracotta” pot in Mid-Europe) in some electrolysis experiment.
    It’s porosity lets ions pass but the solutions/reaction results not (ok, at least exchange is negligible), and perhaps it even has intrinsic ion-exchanging properties. Kind of poor man’s Nafion “membrane” (https://en.wikipedia.org/wiki/Nafion).
    Cannot tell whether clay better lets through cations or anions tho…
    Maybe one could kind of “dope” the clay so it’s conductivity for one ion type increases, exactly using some of the proposed metal ions here?

    I know, this is very off-topic, but I felt triggered by the word “clay” 😀

    • Which also explains why one might not use glazed clay in an electrolysis, also having been mentioned here. It would likely be all but electrically insulating.

    • Apologies for being sloppy and not obeying by the “be nice!” rule by carelessly using “triggered”.
      Triggered was the absolutely wrong word, it is not something to be used in a peaceful good context as this.
      I meant to say “obliged to add my comment” or something like that, in a humorous, nice sense.

      • it’s a sad commentary on current social conditions that you had to censor yourself and apologize for using a perfectly good word because someone might be offended by it.

          • I stumbled upon this: https://www.urbandictionary.com/define.php?term=Triggered

            “To be ‘triggered’ is NOT to be offended by something. It’s actually quite different from that. To be triggered is to have a certain stimulus, be it a word, a place, a person etc, set off (or trigger) a memory linking back to a traumatic point in your life […]”
            (from one of the meaning explanations)

            That is hefty and I didn’t know that. That’s why I have misused that word in my happy context.

            Anyways, back to colors =)

          • deja vu, better english because its more precise; used for exactly this purpose.
            To be fair english has an absurdly large vocab due to stealing words from waves of immigrants from all over the world over millennia.
            A german friend of mine asked what “meander” meant, and when told pointed out there were (in his experience) many words of precise meaning like this that do not exist in german (some like ‘in’/’on’ the other way round).
            Nice, but makes english hard to learn when there are words that have no exact equivalent in your native tongue.

          • Given that English has incorporated words from everywhere (‘apartheid’), can’t blame German for borrowing it back. The German word for meandering is maeandrieren

          • Albert,
            I’m not so sure about that as Mäander and mäandern (German) comes from Latin and before from Greek from the river Μαίανδρος (Maíandros), Turkish Büyük Menderes.

          • Ooops….

            Oh well, so many words in so many languages even native speakers cannot be expected to know the entire vocab of their own language!

          • Yep, it’s not always easy since I’m not a native as well.
            But for that reason we can talk together and kind of describe the meaning, or it becomes obvious from the context itself.

            Thank you all for your inputs and friendly discussion.

  28. Blue.1. The old masters used ground lapis lazuli which was very expensive due to its remote location. Commissioned works would take this into account, and the wealth of the patron could often be gauged by the amount of blue in a given oeuvre. A full length robe as opposed to just a blue shirt, by way of example. Depictions of the Virgin were usually quite extravagant in this regard.
    2. Chartres Blue used in the cathedral’s unparalleled stained glass windows continues to defy the experts as to how it was formulated.

    • I thought the Chartres Blue was heavy on cobolt when they tested it?

      It is insanely blue.

      • Right, Carl:
        “Problem with medieval recipes is that they often don’t makes sense, because terminology is confusing, like for example the idea that sapphire was added in making stained, glass, when this was also latinized name for saffer, which was name of cobalt oxide.”

        For that reason Chartres didn’t become my favorite cathedral, as too much is too much, and Chartres Cathedral is dark. A true jewel is Salisbury Cathedral because of its archtecture and lightness.

    • So, the expression insanely blue hits the nail here.
      Chartres attracts all sorts of mystics from Germany. It has become the most hyped cathedral in Eurpope. Next church is Sainte Chapelle in Paris for similar reasons minus mystics.
      They have a strange habit in France which I hate like nothing: Son et lumière. This atrocity is done to Chartres Cathedral at night. I’ve never seen this atrocity in England, Spain or Italy. It is next to crazy.
      But anyway, the most impressive of all gothic cathedrals in Europe, is, imho, Canterbury. You can spend hours there and not be done. But this is now far from colour and pottery. This is architecture and history and therefore – I know – strongly ot.

  29. 1. A lot of them are oxides, yes.
    2. color is dependent on both the oxidation state AND the elemental colorant. So the exact chemical formula is what matters.

    The first article I linked (on the chemistry of paint) had some other examples of specific compounds being associated with specific colors.


    3. Good question for any glass blowers out there about the melting temperature and color stability.

    • Hmm, I see.
      So even if you kept the same oxidation state it would not give the same color if just the oxidant was different?
      Suppose FeCl3 vs. FeBr3 for instance, as they both have Fe 3+ ions they are in the same oxidation state, but obviously the oxidant is different…

      I bet a lot comes down to how many compounds can “play” with their electrons in that d shell.

      • Pretty much if in ionic state. However note that in glass many may be covalent and this will give different effects. The real world of complex silicates doing strange things in complex molecular ways of chains and strings is what makes rocks interesting.

        • Some of it has to do with crystal structure (when in that state) and I guess the relationship between the chemical (while not in a crystal) and the situation around it (is it in water? in another rock substrate?)and what kind of light it reflects/refracts/absorbs.

          Some chemicals fluoresce, as well.
          For example, luciferase.


    • Please note the high toxicity of many colours.
      Cadmium yellow is banned in the UK for eating utensils (probably chromium too by now) due to dignificant amounts leaching into acidic food (not least yellow is popular for childrens crockery).
      Also not most of these salts would not survive the kiln other than as new silicates/carbonates.

      • I’m mostly familiar with cadmium-based colors in oil paints. Yes, toxic, and shouldn’t be used for anything relating to food.

  30. Unless fired under argon any of these compounds that is not an oxide will quickly become one. Also as stated cadmium is toxic, and so is chromium if it is in the +6 oxidation state, so no go there. Out of all of those colours probably only the cobalt based colors and chromium green would be unaffected by a firing, alongside the simple oxides. I suspect TiO2 would turn into glass just like SiO2, they are very similar chemically, although I have not actually seen this done before. Most of the others would be destroyed by a hot oxidizing atmosphere though.

    • TiO2 is pure opaque white, in every can of paint!
      Complex silicates may have colours I guess. Possibly blues.

      • So is SiO2 if it is powdered 🙂 Opacity I think comes from it being small particles, because white things are often transparent as a pure bulk solid.

        The powder is widely available but as far as I know I have never seen it as a bulk solid, it isnt used in that application like SiO2 or Al2O3, maybe it has poor mechanical properties, though more likely it is just that silica sand is cheaper. Still, maybe someone should try making glass but using TiO2 in place of SiO2 and see what happens 🙂

          • Zinc oxide is also used as sunscreen.
            Hardcore stuff, for the redheaded surfer dude.

          • But real stars use titanium. Really. Cool stars from TiO in their atmosphere, and it reflects a lot of their visible light back inside. It is one reason why red giants are so red.

    • Yep, tell me one in those two pictures that isn’t very toxic somehow, except maybe for plain carbon and iron oxide =D

      But lovely colors they do!
      Cadmium is top-notch anyways, very toxic and makes for 4 different colors 😀

      • Chromium III oxide is not toxic, it is what makes stainless steel stainless. Titanium dioxide is in basically everything to make that thing not transparent, it is also basically non toxic. Zinc oxide is also not toxic or dangerous as long as you dont eat it.

        Prussian blue is actually also not toxic, even though it contains cyanide groups. Cyanide is toxic because it sticks irreversably to iron in hemoglobin deactivating it, but if it is already stuck to an iron atom it is where it wants to be already and is not going to leave easily. Needs to be free CN- ions, or HCN.

    • If I remember correctly Ti02 will become either pink or gold depending on the temperature.
      “Rosé Gold” is often just stainless steel coated with Ti02, it is more pink than real rosé gold.

    • Question woud be massive massive hot ejecta plume from Chicxlulub generate any ligthning? Well at start its 18 000 to 20 000 C rock vapour plasma, But as the hot tephra cool and condense into glass droplets .. woud there be any ligthing in the impact plume?

  31. The Old Masters in Venice and used colours that potters, glassblowers and textile dyers used as can be seen in a description here about an exhibition in 2006. They bought them at the same places of coloursellers, and Venice, being leading in glass (see Murano) was also leading in colours:
    “”Chemical analyses of paintings have shown us that Venetian artists took advantage of the range of materials that could be found at the color sellers to produce paintings that had vibrant and brilliant colors,” Berrie says. “These materials included colorants that aren’t normally associated with oil painters, such as frit, a partially fused glassy colorant used for glazing ceramics or decorating glassware.”

    Jacopo Robusti (October 1518 – 31 May 1594) detto Il Tintoretto, one of the greatest Venetian painters, was in fact the son of a dyer.

    Sand was also used:
    “In the early 16th century, Venice was the world’s center of glass production, and pulverized sand, an essential ingredient in glassmaking, was widely available and might have been sold at the color seller shops where Lotto traded. This bit of serendipity is relevant because Lotto improved the working properties of his paint in an innovative way. While some of his contemporaries used chalk or glass to give paint body and more transparency and to shorten drying time, Lotto added finely ground sand to his pigments, especially to his glazes.”

    “Red lake pigments were but a few of the scintillating colors for which the Venetian artists were famous. Other notable colors, Berrie says, were the orange tones made from two sulfides of arsenic—the yellow orpiment (As2S3) and the reddish orange realgar (As4S4). In nature, orpiment and realgar occur together, but they were chemically separated and prepared as two different colorants by the Venetians. Ultramarine, which was imported from what is now Afghanistan, was another signature color.”

    So Titian’s and Lotto’s legendary reds and Bellini’s deeply moving blues have a lot less to do with the origine of the colour itsself, but instead with the technique of copying from glassblowers and also with the flourishing Venetian colour trade and with exchanging knowledge between dyers, glassblowers, potters and painters.


    Note the shades of red and the blue tones in Tintoretto’s picture “The Miracle of the Slave”, wik. commons:

    • So, what she’s doing here, the young lady, is asking in a good forum. This is like going to the dyers’ market in Venice.
      In fact they fared better. They all had their own traditions and styles, Venice, Florence, Genova, Rome and Spain with Naples and Sicily, and there was exchange, a fruitful inspirational exchange and also competition. That was the better system, and it was globalized.
      What globalization is supposed to mean today (uniformity) won’t work. Such young people will always bring forward new ideas in a world which is getting uniforme, and one day, I hope, we’ll have a vibrant renaissance with different ideas, different opinions and miore sophistication.

      • Apparently trade was done within a banking system in florence using an internal (banking) currency that allowed trade europewide (and beyond). So local bankers/traders could carry goods to (say) Paris and sell them in franks then deposit these at the local guild bank as a credit (presumably so they never carried much gold) and at the year end there was a great reckoning up where it was all converted into the internal currency (not Florins, I think). Its why florence was so important as it allowed safe efficient trade and banking. I think they also invented double entry book keeping.

  32. I have read an article about the various colors of volcanic rock along the Queen Ka`ahumanu highway in Hawaii and read that blue volcanic rock is bad because it is really hard.
    Now I am quite curious if there is a volcanic rock that is really blue and not just a tint of it. Looked for it on the internet and looks like a possible candidate is a volcanic rock that has a lot of sodalite in it, even though it only exists as plutonic rock (could be wrong?). Is there anything else that would make volcanic rock blue?

    • Don’t think so.
      Lazurite (Lapis Lazuli), for a time also falsely called Azurite, is derived from the word lajvard, meaning blue in Farsi, and a ggl search leads me straight to the Badakhshan Province, an old Afghan province (today small parts belong to Tajikistan and China).
      Lazurite, not to be confused with Azurite (Cu3(CO3)2(OH)2) or with Lazulite ((Mg,Fe2+)Al2(PO4)2(OH)2) is therefore traditionally from the Lapis Lazuli District of Badakhshan where it has been mined!!!! for 6000 years.

      About 10.000 years old artifacts have also been found in Bhirrana, Indus District.
      Other mining places are Lake Baikal, Vesuvius, and some places in Burma, Canada and the US.
      Lazurite, says wikipedia, is a product of contact metamorphism of limestone and is typically associated with calcite, pyrite, diopside, humite, forsterite, hauyne and muscovite.

      And limestone rings the subduction bell. The area without Canada and maybe the US is the region where the Tethys Ocean subducted, so there was once volcanism of course. Today the area with volcanism is before all, Vesuvius and maybe the places in the US, but ongoing volcanism is no conditio sine qua non, on the contrary as nobody would mine in active volcanoes. As mining is mentioned it would not be easy to find it by just scraping off some rocks.

      “By the end of the Middle Ages, lapis lazuli began to be exported to Europe, where it was ground into powder and made into ultramarine, the finest and most expensive of all blue pigments. Ultramarine was used by some of the most important artists of the Renaissance and Baroque, including Masaccio, Perugino, Titian and Vermeer, and was often reserved for the clothing of the central figures of their paintings, especially the Virgin Mary. Ultramarine has also been found in dental tartar of medieval nuns and scribes.”

      So Lapis Lazuli and Lazurite is basically the same and contains also hauyne and was first known in Afghanistan.

    • Whilst geothermal energy is essentially unlimited, unless there is a fluid moving to encompass a huge volume of rock, the rock soon cools so as to be useless. I imagine the icelandic geoplant earthquakes are in part because they are continually fracking to reach new areas of hot rock as the old rock is chilled.
      Too many think its cheap free and universal energy, oh that it was that easy.

      • The trick is to have more boreholes than needed at inception of the plant, that way you can rest boreholes and let them reheat.
        Obviously this comes with added cost and must be implemented in the cost vs profit-calculation at getgo or you will end up with either an unprofitable plant, or a plant with diminishing return over time (like Larderello).

        And now, guess what I have been doing for the last couple of days… I need to get a life. 🙂

        • Thermal conduction over km distances through dry rock is surely not a great way to get high heatflows? The actual usable energy in many dry geothermals (ie non-recently volcanic) must be relatively limited to the thermal capacity of a few km^3 of rock and a few hundred C. Now I haven’t done the sums for this but domestic land thermal store systems are not very effective because the energy need is relatively big even just over a winter for one house.

  33. Earth and Venus:

    “Over time, one increasingly draped itself in the greens and blues of life, while the other became enshrouded in toxic haze.”
    minute 47

    Venus, questions, perspective for future missions. I enjoyed the film, several specialists on board.

    • When Venus got too hot for rainfall.. there where No sillicate co2 weathering scrubbing, and all Co2 from volcanoes just keept building up into the atmosphere .. without being scrubbed away

      The next global lava flood resurfacing May add another 10 atmospheres of CO2 and raise surface temperatures to 750 C

      But the buildup of volcanic CO2 in Venus atmosphere have probaly been slowly ongoing ever since it got too hot for rainfall

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