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PeterH

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  1. 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
  2. Is this of any help? http://aakilns.com.au/pdf/novaman1.pdf 1st page is
  3. 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
  4. Background Some reasons why you might want to use clay vessels in winemaking today are given in https://www.winemag.com/2018/05/30/aging-wine-in-clay/ Clay is the happy medium between the two. Like oak, clay is porous, allowing for an exchange of oxygen. Like steel, clay is a neutral material, so it doesn’t impart additional flavors. I think that Roman wants to get a porosity "similar to that used in terracotta winemaking vessels". Or at least an indication of just how dry/damp/soggy an earthenware body fired to bisc would be when filled with liquid. I seem to remember that the forum has reported earthen pots leaking/seeping sufficiently to damage the surface they are standing on (after the waterproofing glaze has crazed). (Aptly enough it's in the thread vases leaking water!) Regards, Peter
  5. I suspect that the long history of clay use in wine making is simply because for most of human history clay has been the default choice for storage vessels and such. Wiki indicates amphora have been used since neolithic times . https://en.wikipedia.org/wiki/Amphora Some reasons why you might want to use clay vessels in winemaking today are given in https://www.winemag.com/2018/05/30/aging-wine-in-clay/ Clay is the happy medium between the two. Like oak, clay is porous, allowing for an exchange of oxygen. Like steel, clay is a neutral material, so it doesn’t impart additional flavors. Regards, Peter
  6. As liambesaw says strontium is used in fireworks because of the distinctive colouration it gives to flames. https://en.wikipedia.org/wiki/Flame_test
  7. If you've got it down to Dolomite vs Whiting ... What temperature do you normally fire to? If it's cone 6 you might try this from https://digitalfire.com/4sight/material/calcium_carbonate_173.html The difference between dolomite and calcium carbonate in a glaze These glaze cones are fired at cone 6 and have the same recipe: 20 Frit 3134, 21 EP Kaolin, 27 calcium carbonate, 32 silica. The difference: The one on the left uses dolomite instead of calcium carbonate. Notice how the MgO from the dolomite completely mattes the surface whereas the CaO from the calcium carbonate produces a brilliant gloss. Advice offered from a position of complete ignorance, use at your own risk.
  8. Slight thread drift, but there is more info on the contents of p209 pehatine in https://www.hot-clay.com/media/attachment/file/v/i/vitraglaze_mixing_medium_msds.pdf In % weight Water >90 Natriumcarboymethylcellulose 0.1 – 5.0 Calcium bentonite 0.1 – 5.0 Hydrocolloid preparation 0.1 – 3.1 from the given CAS this is Propylene Glycol Chlorxylenol 0.05 – 0.1 a disinfectant Tin oxide superlite 0.01 – 0.1Propylene Glycol Love the wide ranges PS The sheet for pehatine 209 (no p) is at https://www.milton-bridge.co.uk/images/pdf/Pehatine-data-sheet.pdf Looks very similar, but dropped the propylene glycol and added a 2nd biocide
  9. Is this any help? Those Unlabelled Bags and Bucketshttps://digitalfire.com/4sight/education/those_unlabelled_bags_and_buckets_134.html
  10. Included for completeness, rather than advocacy.Just to say that some googling indicates that [at least some] gas-fire "coals" are based on ceramic fibre. Which might give another possible approach: with its own technical and H&S issues.
  11. 2013 discussion on Something Exploded in the Kiln - Was It Clay fatigue? http://cone6pots.ning.com/forum/topics/clay-fatigue
  12. I remember some people having strong feelings that e/w & s/w should be bisqued at different temperatures, in order to have the same absorbancy when glaze-dipping. [In the context of fairly high-fire s/w.] I suppose that it makes sense if you have high throughput and are only using two clays. Regards, Peter
  13. I would suggest starting with DIY ink -- oil+pigment (a mason stain sounds good[1]). [2] .. and an image with some largish 100% back and 100% white areas. Everybody seems to say no to inkjet printers. Some [all?] Xerox and Laser printers produce a fused plastic image that is likely to be good at rejecting water and being receptive to oil. While inkjet inks may be water-soluble. After you've applied the gum-arabic solution and let things stand for a while you should see that the paper in the white areas has absorbed the solution (e.g. looks translucent). It needs to do this to repel the oil. Regards, Peter [1] Use an oxide until you've got the hang of things, if you don't have any to stain hand [2] Ideally it should be what's known as a drying oil. Several are listed in https://en.wikipedia.org/wiki/Drying_oil. These can be bought (fairly expensively) as artists supplies. Oils sold for cooking are cheaper. However as long shelf- life and optimum drying properties are mutually exclusive the cooking oil may be denatured [to prevent it going rancid too fast after opening]. Personally I would start with something like walnut oil from the local supermarket. ... remember drying properties are pretty academic until you get the transfer process working. For production use an artists/woodworkers/decorators linseed oil might be technically better. Up to you to judge the cost/performance balance. But be aware that rags soaked in the more drying oils can [and sometimes do] burst into flames, and have been the cause of some expensive fires (linseed and tung oil in particular). [AFAIK keep rags in a small screw-top jar. If things start to go downhill the oxygen is depleted before the temperature rises too high.]
  14. Lithography is based on the fact that oil and water don't mix. The gum-arabic solution provides the water-based part, so you need to use an oil-based ink. A printable description of the process can be found at https://pistrucciartworks.wordpress.com/2011/03/20/photolithography-on-clay/ Regards, Peter Hope you have more success than I did. Lithography works better with high-contrast images, and sometimes fudges such as half-toning are required.
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