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Everything posted by PeterH

  1. CMC powder is available at https://www.bathpotters.co.uk/cmc-finnfix-organic-polymer/p3690 This may be of interest V gum T, but 1Kg https://www.scarva.com/en/Scarva-Raw-Materials-Vee-Gum-T/m-6517.aspx
  2. FYI, as somebody has mentioned hydraulic presses ... These tile-makers considered making the DIY press described in Handmade Tiles by Frank Giorgini, but instead added press plates to a cheap commercial press. https://createniks.wordpress.com/2010/04/24/hydraulic-tile-press/ ... less powerful/cheaper presses are available! Two addenda on their first tile mould. https://createniks.wordpress.com/2010/05/13/first-mold-for-the-tile-press/ https://createniks.wordpress.com/2010/05/20/our-tile-press-rocks/
  3. Any chance of a photo of your "canisters"? Some shapes are easy to cast, some harder.
  4. You might be interested in this item from over at the Ceramic Arts Network. Flat Tiles The Easy Way https://ceramicartsnetwork.org/daily/pottery-making-techniques/making-ceramic-tile/flat-tiles-the-easy-way/ It recommends 8-12 hrs on drywall and then a wire shelf.
  5. Hamer&Hamer mirror Min's concerns on wreathing and deflocculation. https://tinyurl.com/yyx5z39l However they add that "swirling the remaining slip around the mould before draining may help to overcome the problem". PS for what it's worth Valentine's recommend an identical slip recipe for use with their Fine Bone China Granulate. https://www.valentineclays.co.uk/product/fine-bone-china-granulate When making casting slip from their plastic clays they recommend using both sodium silicate and soda ash for all except the bone chinas. Irritatingly they also give suggested control parameters for all but the bone china. https://www.valentineclays.co.uk/sites/default/files/downloads/Technical Analysis Chart - Industrial Products.pdf
  6. You are absolutely right, I very much doubt that doped crystals could reconstitute themselves, even if the firing conditions were ideal for recrystallization of the host crystal itself. Regards, Peter The "why they mixed it with alcohol rather than water" point I'm less clear on. I mentioned it in case anybody else could spot it's significance (if any). As you bring the point up I'll elaborate on my position. I didn't believe that strontium aluminate was water soluble, but I couldn't find a handy reference giving an actual number. I did find several data-sheets claiming that it was insoluble in water -- but also one that suggested that is was soluble in water. However use of water-based media such as acrylic seems to be recommended for the pigments. So my current belief is that water solubility just isn't an issue. I suspect that the chemists used alcohol-based techniques in the preparation of the glaze because (in their line of work): - It's what they are used to doing (accuracy and reproducibility are important to them, so tried-and-tested is rightly valued) - You can evaporate alcohol easily, especially with a mild vacuum (time is money) - The cost, H&S and waste-disposal issues are insignificant in a lab context But that's probably because it's the only vaguely plausible explanation I can come up with.
  7. This paper discusses a low-fire glaze for strontium aluminate based pigments. https://tinyurl.com/yyvafwbl Bottom line is 80% borax, 10% potash feldspar & 10% kaolin. Consistent with my suspicion that high-alkali glazes might be best avoided as they might attack phosphor grains. Presumably needs reformulation ... non-soluble ... frit based.
  8. Just wondering, if he is a lapsed member a p.m. may not get his attention. Is the any way for [a moderator?] to send an email?
  9. Sure do, and probably the easiest way to go. You can also mix the pigments with a wide range of mediums, e.g. acrylic. https://glowtec.co.uk/starglow-powder/
  10. Don't know about lustres, but there was a flurry of interest in "glow in the dark" glazes some years ago. I even saw small quantities of the phosphors for sale, with low-fire glaze recipes. Sadly a quick look didn't find anything currently available on the retail market. Probably a fair amount available wholesale from China! Like most "luminous" substances they probably require some exposure to sunlight/UV to "charge" them. A few urls to give you the idea: https://ceramicartsnetwork.org/wp-content/uploads/2009/02/cmjja04glowingglaze.pdf http://www.potters.org/subject94692.htm http://www.gtamart.com/mart/products/phspgmnt/glaze.html http://www.luminggroup.com/english/product/index.asp?sid=165&sel_id=151&sel_id_02=165 There seem to be other pigments (perhaps glazes) that simply glow under UV light. https://www.darkniteglow.com/product/uv-light-reactive-powder/ Regards, Peter PS A search with a more scientific terminology "photoluminescent glasses" found https://tinyurl.com/y2aw55bo The ones based on strontium aluminate may well work in a low-fire glaze which doesn't dissolve it. ... wiki gives "temperatures above 1090 °C is likely to cause loss of its phosphorescent properties" Vaguely relevant paper https://pdfs.semanticscholar.org/6ecd/665a0fcfe721fd4431e40583faac200e80fc.pdf ... which unfortunately doesn't seem to say what glaze they used, nor why they mixed it with alcohol rather than water.
  11. Agreed, a great book. As it has been (re?)printed by several publishers it is perhaps best to give your library the title rather than details of a particular edition. Handmade Tiles: Designing, Making, Decorating by Frank Giorgini You can see the contents list at: https://books.google.co.uk/books/about/Handmade_Tiles.html?id=PYrh8-kBNYEC&printsec=frontcover&source=kp_read_button&redir_esc=y#v=onepage&q&f=false The first chapter, being a historical overview, gives a rather misleading impression of a very practical book. BTW Bookfinder lists second-hand copies of the book at ~$4. https://www.bookfinder.com/search/?full=on&ac=sl&st=sl&ref=bf_s2_a1_t1_1&qi=eOQzb.AaQGULEGlA0YmFzKCBwI8_1497963026_1:7:2 ...you may need to do a new search with your own currency and location. Regards, Peter PS You might try contacting the originator of this thread, if they are still about:
  12. No, a space between the walls is not normal. Indeed if you use the normal "drain casting" methods there is no way for this to happen. What you seem to have is a mould that relies on "solid casting", in which both the inner and outer layer of your bowl are cast against plaster, as in this plate mould. If you just fill a mould like the bottom one with slip you are in trouble. The original slip shrinks as the mould draws water out of it, leaving air holes. So you must keep topping up the mould with slip until the solid-cast portions are completely full of drying clay. (Sometimes the mould is designed to hold all the extra slip required, in which case you don't need to top-up.) Solid casting a a bit trickier than drain casting: it's more demanding of the quality of slip, and usually has concave sections that you need to de-mould as quickly as possible (and no sooner!) to avoid them sticking in the mould. This web page describes the process: http://butterflyceramic.blogspot.com/2013/01/a.html Regards, Peter PS Here is a video of somebody filling a solid cast plate mould. Note the fluidity of the slip, and the ease with which it passes through the caster's sieve. Of course you cannot just dilute your slip to that consistency with water, it has to have both the right clay:water ration and state of deflocculation. ------------------------------- Sorry, cannot get rid of this dratted image/attachment, please ignore.
  13. I've not heard of anybody using MICR ( Magnetic Ink Character Recognition) toner for for decals, but it has always seemed like a good idea: guaranteed very high iron content, and its not going to suddenly switch to an iron-free formula. You might want to glance at their site before you phone, to get the most out of the call. Range of printer manufacturers supported and explanation of what MICR toner is: https://www.lasercartridgeplus.com/micr-toners.html Explanation (down the page) of how they get the cartridges to refill with MICR toner: https://www.lasercartridgeplus.com/hp-micr.html PS Don't know if they can send you a sample printed "cheque"; you might be able to test-fire the image onto a tile. (William De Morgan did this using tissue-paper+glaze, don't know if printer paper would work.)
  14. [I may be reading your ref too quickly, but is seems to say metallic barium melts at ~ 1300F. However as wiki gives the MP of BaCO3 as 811C (1,492F) your point remains a good one.] Many years ago I was astounded to read that quite a lot of the barium sulphate in a Jasper body survived the firing. I'd assumed that it would simply decompose. Trying to find a reference I looked in "Ceramic Masterpieces" and found this: During firing at a temperature of about 1250C, a portion of the barium sulfate reacts with the clay components to form a barium-aluminium-silicate matrix containing residual barium sulphate particles. The matrix is a mixture of a glass with fine particles of barium-aluminium-silicate (celsian) and barium silicate (sanbornite) ... From which I assume that the barium sulphate in the body either remains unchanged† or enters into the molten glassy matrix liberating SO3 (later the barium micro-crystalises out on cooling). It would make sense if the barium carbonate in a glaze did much the same. So in high-alkali raku turquoises the BaCO3 would be completely decomposed, while in a full-blown barium matt perhaps some unchanged BaCO3 remains. Just a guess. Regards, Peter † Wiki gives the MP of BaSO4 as 1,580C (2,880F) and https://chemiday.com/en/reaction/3-1-0-3287 gives the decomposition temperature as "over 1580C".
  15. Min, I think that both you and Digitalfire are right "up to a point". After some googling ... From http://chemisphere.co.uk/index.php?route=product/product&product_id=57 Loss on Ignition (800C x 1hr) 0.4% Max From https://books.google.co.uk/books?id=Qq3zCAAAQBAJ&pg=PA129&lpg=PA129&dq=barium+carbonate+loss-on-ignition&source=bl&ots=xK72KoHSho&sig=ACfU3U3_HZ2qQlEQnFWpoocnIHDJWmwSFg&hl=en&sa=X&ved=2ahUKEwi8uba9n9_jAhVIQ8AKHU-JCQcQ6AEwC3oECAkQAQ#v=onepage&q=barium carbonate loss-on-ignition&f=false Loss on ignition 22.3% ... decomposition of BaCO3 at 1450C (2640F) So the potential LOI is, as you say, 22.3%, however how much happens depends on the temperature use (and no heat-work). See fig2 in http://www.scielo.br/pdf/ce/v54n331/a0154331.pdf Finallyhttps://www.chemguide.co.uk/inorganic/group2/thermstab.html discusses why the dissociation temperature of the alkali metals increases Mg<Ca<Sr<Ba in terms of the larger ions having less ionic potential and hence less polarising effect on the carbonate ion.
  16. What conclusions are you reaching? I can see #1 & #3 fitting in with your ideas of carbonates. However #5 at 53% LOI looks "interesting/surprising".
  17. DAISO also seem to be online https://www.daisojapan.com/c-139-brushes-accessories.aspx
  18. > I'm sort of getting bored of the glazes available to be made at cone 6 ... Have you tried any of the slow-cooled/downfired ones? Slow Cooling by Norm Stewart https://cone6pots.ning.com/forum/topic/listForContributor?user=0ng9vrmzioqmi Gas kilns use hard fire-brick which cool far more slowly than the foam-core brick used in electric kilns. Many here have suggested this is one major difference in the "cone 10" look of a gas kiln.
  19. I admire your persistence. A video of some flame tests, which might give a better idea of what it actually looks like than "best still photos". I'm not sure why you think measuring specific gravity is a huge pain in the butt. You may be right, but theoretically it doesn't seem that difficult. For example: - Take a measuring cylinder (cheapish on ebay etc) and part fill with water, then read volume. - Add a given weight of powder, and read volume. - S.G. = weight/((density of water)x(difference in volume)) Never done it myself, but sounds pretty foolproof - Measure volume from the bottom of the meniscus. e.g. https://www.911metallurgist.com/blog/how-to-read-a-burette - Need fair quantity of powder for accuracy, and all should be below waterline. - Requires the powder to be easily wettable with no air pockets. - Maybe add a drop of wetting agent (d/w rinse aid or washing up liquid). - Maybe do it twice to get an idea of the accuracy.
  20. I wondered if the combination of a weak acid and rather "rocky" mineral might mean that dolomite does not give a strong bubble test. This reference seems to confirm some of these concerns: The "Acid Test" for Carbonate Minerals and Carbonate Rocks https://geology.com/minerals/acid-test.shtml Acid Reactions of Carbonate Minerals Mineral Chemical Composition Cold Acid Reaction Warm Acid Reaction Aragonite CaCO3 strong strong Azurite Cu3(CO3)2(OH)2 yes strong Calcite CaCO3 strong strong Dolomite CaMg(CO3)2 weak yes Magnesite MgCO3 very weak weak Malachite Cu2CO3(OH)2 yes yes Rhodochrosite MnCO3 weak yes Siderite FeCO3 very weak weak Smithsonite ZnCO3 weak yes Strontianite SrCO3 yes yes Witherite BaCO3 weak weak Table 1: A list of commonly and occasionally encountered carbonate minerals with their chemical formula and reactions to cold and warm hydrochloric acid. Test results can vary because of weathering, previous testing, contamination, and specimen purity. The effervescence using vinegar usually requires a hand lens for clear observation and is only observable with carbonate minerals that have a strong reaction with hydrochloric acid. Maybe try leaving a small quantity in excess hot vinegar overnight? Even add a little detergent at the start and look for foam at the end?? Peter PS Have you tried measuring LOI or specific gravity yet? From digitalfire's list dolomite has a massive 46% LOI (bone ash has zero). So well worth measuring LOI, only other high LOI's in the list seem to be carbonates, alumina hydrate & cobalt oxide.
  21. Stumbled across this oddity, ZnO changing colour when heated. PS The temperature dependence here is because this is a band-gap colour. The causes of colour https://www.physics.utoronto.ca/~phy189h1/Causes of Color scientificamerican1080-124.pdf The origins of colour in minerals http://www.minsocam.org/msa/collectors_corner/arc/color.htm
  22. Very distant schoolboy memories slowly resurfacing ... flame tests are very good for identifying some metals. Calcium gives an orange flame test and magnesium a colourless one. https://en.m.wikipedia.org/wiki/Flame_test
  23. Is this of any help? http://aakilns.com.au/pdf/novaman1.pdf 1st page is
  24. Interesting twist to the porosity story. Kvevri – Wine Making in an Earthenware Jar 6000 B.C. https://winehistoryproject.org/kvevri-wine-making-in-an-earthenware-jar/ They used a large clay jar that could hold 2,000 to 2,300 gallons of wine. (Giving a large volume to surface ratio, and minimising the effects of porosity.) Even so the large vessel was lined with bees’ wax to seal the interior walls and base to make it airtight which helped to protect the wine from spoiling. More on historic & modern Georgian practice in https://www.bluedanubewine.com/pdf/qvevri_eng_Q.pdf This includes details of the waxing process, and the importance of thorough cleaning. Regards, Peter PS snippet relating to one wine producer: https://books.google.co.uk/books?id=VXgDPNccjGgC&pg=PA139&lpg=PA139&dq=Cornelissen+epoxy++resin+wine&source=bl&ots=9Lg9ijwzPc&sig=ACfU3U3kYXFl1AcQrW4qX9vfmFNvk2M_Fg&hl=en&sa=X&ved=2ahUKEwjCprf0tbXjAhWMi1wKHa94DwIQ6AEwEXoECAgQAQt Blurb on Cornelissen at http://www.wineanorak.com/magma.htm
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