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PeterH

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  1. PeterH

    Clay fatigue?

    2013 discussion on Something Exploded in the Kiln - Was It Clay fatigue? http://cone6pots.ning.com/forum/topics/clay-fatigue
  2. PeterH

    Bisque firing earthenware & stoneware

    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
  3. 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.]
  4. 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.
  5. What did you do with the Indian ink?
  6. Can you confirm that your power supply is 220v? [1] How would you feel if the 1-phase power was 3.0 kW rather than 3.6 kW? Regards, Peter--- From the US site discussed by Bill Kielb the 3.6kW seems to be for a 240v US power supply. With the same elements on a 220v supply this gives 3.0 kW (P=iV=V^2/R). [1] Only if you really want to know... A quick google will give the impression that the whole of Western Europe receives a 230v power supply (https://www.worldstandards.eu/electricity/plug-voltage-by-country/). While it is true that the power companies conform to the appropriate 230v European standard, this simply means that any voltage in the range 206.8v-254.4v is allowed. My understanding is that the power companies simply continue to supply the voltages they have been using since WW2; ~220v for mainland Europe, ~240v for the UK (https://www.schneider-electric.co.uk/en/faqs/FA144717/).
  7. Hi, You might like to try this. You will need: - A metal canister open at one end a little bigger than your pot. - Two pieces of chipboard big enough to cover the end of the can. - A brick or two. - A newspaper about 1/4 inch thick. - A bucket of water. - Rubber bands or string. - Some charcoal. - A plastic shot glass or similar. - Some alcohol (UL meths, US ??) - Place the first piece of chipboard on the ground, with the tin on top. (This insulates the tin a bit.) - Cover the bottom of the can with charcoal. - Put the newspaper into the bucket of water to soak. - When it's getting nearly time to take the pot out of the kiln take the newspaper out of the water. Let it drip a bit then wrap it round the chipboard and secure it with the rubber bands or string. You should have a nice flat region of paper that will securely seal the lid of the can. - Fill the shot glass with meths. - Take the pot out of the kiln, and place it in the tin on top of the charcoal. Keep it away from the sides. - Rapidly: - Pour the meths into the tin. [H&S keep your head well clear, and wear something like a leather glove.] - Place the wet newspaper over the tin to fully seal it. - Put a brick or two on top to ensure the seal it good. WAIT until it cools. Then open the tin. You should be surprised how big a vacuum has been generated, and the tin should have left a clear compression ring in the newspaper. Hopefully the pot should be reduced. If it was a copper-matte "glaze" you may have reduced it so far that there is a layer of metallic copper. You can carefully reheat this in an oven and watch the colours develop. Unfortunately they fade with time. PS-1 A tin may be too weak and implode with the vacuum. I used stainless-steel tea-caddies from a charity shop. You may want to try reducing the degree of reduction. You might try less meths, open sooner, etc. PS-2 I've explained [sic] my limited understanding of copper-matte glazes in post #5 of http://community.ceramicartsdaily.org/topic/4701-copper-raku-matt-glaze/?hl=%2Bpeter+%2Bmatte&do=findComment&comment=42291 PP-3 Dedicated to the memory of Heath Robinson. https://businessenglishlessonplans.files.wordpress.com/2012/04/self-operating-napkin.png?w=300&h=211
  8. PeterH

    Your Experiences With Stain/s

    Hi, I seem to have failed to make myself clear. I don't know about "cleavage" numerical value ... from 100-150 or so Can you reference an accessible paper/article that has such numbers in it? I don't recognise the term optically negative Can you reference an accessible paper/article that uses the term? That way with some research I should be able to understand your points, and relate them to my current understanding of optics and crystallography. Regards, Peter
  9. PeterH

    Your Experiences With Stain/s

    Hi, At the moment I'm totally failing to relate your recent posting to my understanding of optics, and my sketchy understanding of crystallography. What would help me most is references to online papers that discuss the topics you mention. To verbalise my confusion: All minerals have a "cleavage" numerical value ... from 100-150 or so. - I cannot even image what units these cleavage numbers might be measured in, and I've always thought of cleavage and refraction as being essentially unrelated topics (bar the weak relationship through birefringence). - The only cleavage related "numbers" I can thing of are various cryptographic angles and Miller indices. I had to look up the name of the latter, but they are the bracketed triplets describing crystallographic planes; e.g (101). optically negative properties - A term I'm totally unfamiliar with, although a quick google might suggested that it might relate to birefringent crystals. - I totally failed to find anything linking "optical negativity" to matte/satin effects. Indeed I'd always believed that these were explained by the relative intensities of specular and diffuse reflection. As I said, I hope that reading some relevant papers can help me understand things better. Regards, Peter
  10. PeterH

    Raw Glazing At Cone 6-8?

    >"Glazes Cone 6 1240C" by Michael Bailey >they are rare and not cheap - £12.99 cover price, cheapest on Amazon £34...... You can save a little by using one of the bookshops indexed by bookfinder, at the moment the cheapest are £25.16 new, £22.26 s/h. http://tinyurl.com/j6pbh3m
  11. PeterH

    Porcelain

    Strange, the Scarva site doesn't seem to give any firing cone or temperature. http://www.scarva.com/en/Scarva-Nano-Colours-NPO032-Snow-White-Porcelain-Casting-Slip/m-5490.aspx Does it say anything on the container? If not, I'd try emailing Scarva (as they suggest under the "Description" tag of the referenced page).
  12. PeterH

    Raw Glazing At Cone 6-8?

    You might be interested in Fran Tristram's Single Firing: The Pros and Cons (Ceramics Handbooks). New and s/h copies can be found at reasonable prices http://tinyurl.com/jyucfyp
  13. Preamble - Firstly, I'm not the right person to ask. - Secondly, yes -- in theory -- its as complicated as that. - Thirdly, I don't think anybody normally does it that way. Direct top-of-the-head opinions on your points 1. Need a clay body that vitrifies at my firing temperature. If you want your work to be really functional, otherwise you're relying on the glaze for waterproofing. AFAIK you cannot do this with e/w as normally fired. 2. Know the expansion/contraction of the clay? You wish. AFAIK it even depends on how you've fired it. 3. Know my chosen glaze recipe is formulated correctly for the temperature and melts right and is going to be durable? Ideally. The glaze programs can help (assuming that its a glassy gaze). Things like under-firing a clear glaze to get a matt are not a good idea. Durability has received a lot more attention after Mastering Cone 6 Glazes by John Hesselberth and Ron Roy came out. 4. Know how a glaze recipe will act on my chosen clay (COE)? Some of the glaze programs can give you a estimate of the COE (assuming that it is a well-fired glassy glaze). AFAIK the general idea it to learn what the estimated-COE is for glazes that do successfully fit your body (as you fire it) and aim to formulate new glazes to something like that estimated-COE. In practice I suspect that there is a lot of grabbing recipes from somewhere, finding ones that they nearly fit, and line- blending to a good fit. [Good pragmatics are better than reliance on inadequate theory.] Remember to rub-in indian ink or something when looking for crazing it shows things up wonderfully, even fresh cracks. 5. Test it to be sure with some sort of extreme temperature/freezing/boiling test and durability test? If you're selling to the public it sounds like good insurance. For the hobbyist its still sounds like good practice, especially if you are using a porous body.
  14. I'm afraid not. Indeed counter-intuitive even crystalline silicon dioxide (quartz) and fused silicon dioxide (a glass) have quite different thermal expansion properties. So its not just the amount of SiO2 but also its chemical/crystallographic form. To emphasise the point, fused silica has a low thermal expansion and is the gold-standard for low-expansion heat-resistant laboratory glassware. On the other hand, quartz: Basically a lot of the SiO2 in a body is crystalline silica, and most SiO2 in a glaze is part of a glassy matrix. So its properties are quite different in the two situations. I'm afraid its back to the usual sources of information: https://digitalfire.com/4sight/glossary/glossary_coe_co-efficient_of_thermal_expansion.html https://digitalfire.com/4sight/troubleshooting/ceramic_troubleshooting_glaze_crazing.html
  15. It would be a pity to give up so soon. The deep texture seems such an integral part of those teapots, and Ginger gets it almost effortlessly with her texture mats. Just checking if the state of the clay was approximately as described by Ginger: http://gingersteele.blogspot.co.uk/2010/02/making-handbuilt-cup.html ...and you used a former to bend the slab : http://gingersteele.blogspot.co.uk/2010/02/step-5-making-cylinder-from-cup-blank.html Good luck.
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