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Everything posted by PeterH

  1. Which reminded me of an early paper on local reduction. (ref in https://community.ceramicartsdaily.org/profile/34897-peterh/ ) One of the most interesting ideas was the use of a SiC containing under-glaze (or IIRC body) which then influenced the colour of a SiC-free glaze applied over the bisqued piece. - They give under-glaze/glaze combinations for copper reds at cones 012 and cone 9. - They suggested that silicon carbide achieves reduction-effects over this remarkably wide range by only reacting when in contacted with liquid glaze. I haven't seen this idea mentioned elsewhere
  2. I think that it's the other way round. There are properties of a throwing body which make it less suitable for casting. This is most evident in porcelains, where whiteness, translucency, high plasticity, availability of ingredients, and cost need to be balanced. Higher plasticity tends to result in poorer whiteness and translucency. Extreme throwing-body examples are using rarer and more expensive ingredients, or formulating a marginally plastic body (for accomplished throwers willing to trade-off ease of throwing for a better fired appearance). A casting body doesn't need to be nea
  3. @Magnolia Mud Research That's not how I interpreted the OP's query, and I would be interesting in his response. You are of course right that lasers enable a variety of 3D printing techniques, not least because of their ability to be focused precisely. Ceramic 3D printing seems to be no exception, and 3D printing of ceramics: A review tinyurl.com/45cvhhrk includes details of laser sintering and laser melting applied to the production of ceramic parts.
  4. From p88 of A Guide to the Classification of Medieval Ceramic Forms https://medievalceramics.files.wordpress.com/2019/12/a_guide_to_the_classification_of_medieval_ceramic_forms.pdf
  5. Loosely related modern idea. When ordering drinks at the bar, guests could ask for theirs to served in one of the sculpture's individual compartments. When all three cups were filled, (ideally with drinks ordered by three strangers) the newly-formed trio could cluster together, introduce themselves and forge new connections. Drinking from one compartment without spilling from the others is a challenge that requires communication, coordination and teamwork, akin to a corporate team building activity, albeit a boozy one. http://www.jonsasaki.com/index.php/work/cluster/
  6. A query about heat-work and refiring. What is the effect of simply refiring to the same cone?
  7. Interesting question. Could it get more heat-work by cooling slower? Much of the radiation from the inside a cup will presumably hit somewhere else inside the cup, while radiation from the outside the cup will mainly go away from the cup.
  8. What are the small white dots ringed in this picture?
  9. In my case I was given a mould which ended at the top of the form. So I cast a plaster ring to hold top-up slip and ensure that the vases lip was fully cast. Ending up with something like this ... I just: placed the ring in position; cast; drained; cut against the top of the mould and the inside of the ring; removed ring plus adhering plaster; used a harp with outward pressure to cut the top of the vase; then wiped with a damp sponge (again with outward pressure). This might be trickier for you, as you have less spare space on top of your existing mould. So I was suggesting you cobb
  10. You might also be interested in the What happened and how to limit color variations? thread in Clay and Glaze Chemistry
  11. Maybe take a photo before and after firing. Just in case the results are worth reporting to your supplier.
  12. Is there any way of constructing a test-tile with some of these hard pieces inserted into them, and their location marked (eg by inscribing a circle round them, perhaps by the end of a tube)?
  13. Some people use acrylic medium as an alternative to shellac for water-erosion of unfired pots, as far as I know without any problems in the bisque firing. I imagine that the medium is essentially free of the colourants @Rockhopper warned about. (Add food colouring if you want it to be more visible when painting?) e.g. https://www.grainnewattsceramics.com/porcelain But in this case the shellac/acrylic is used because it stands up the the abrasive treatment better than the usual wax or latex resist would.
  14. In case it's any help there is an analysis in Porcelain body "Audrey Blackman“ https://glazy.org/materials/58805
  15. Sadly the car industry seems to use CNC on oil-clay rather than fire-able clay. Why car designers stick with clay http://www.bbc.com/autos/story/20161111-why-car-designers-stick-with-clay The first thing to know about this marvelous medium is that it isn’t actually clay. “Clay is different waxes with some filler in it,” says VandenBrink. “That used to be sulfur, and more recently small glass beads, but it’s mostly waxes. Honestly, it’s hard to know exactly what’s in it, because the formulas are proprietary.” There are half a dozen companies that make plasticine clay suitable for full-scale d
  16. Found on p5 of https://ceramicartsnetwork.org/wp-content/uploads/2012/08/CA17D_Sample.pdf Often, however, it is best to isolate the clay from the fuel so the smoke can reach all parts of the pot and there is no danger that unburned fuel will blanket some part of the pot and keep it from becoming black. Michael Wisner has developed two ways to accomplish this. To fire outside, he stacks pots on firing stands over sawdust, then covers the stack with a barrel. He builds a fire around the barrel, to create enough heat to cause the sawdust inside to smoke. Alternatively, he can stack pots the
  17. I'm afraid that I don't understand your problem. I would have thought that if you slip-cast a mug the inside would be smooth (assuming that the slip is under control). So a round mug has a smooth round inside, and a polygonal mug has a smooth almost-polygonal inside (with slightly rounded inside corners). Obviously the flange (?) of the lid would have to be tailored to fit within the shape of the inside of the mug. For the polygonal mug this might mean that the flange only makes contact with the flat sides of the mug and avoids the corners. Can you clarify what I'm missing? PS
  18. Loosely related paper on botijos - porous ceramics traditionally used for used for cooling drinking water in hot climates. an ancient method for cooling water explained by mass and ... PS Even containers for chilled snacks, drinks or towels The physics of pot-in-pot coolers https://hal.archives-ouvertes.fr/hal-02408692/document
  19. Searching for 2264 potclays I get a rather cryptic link to FRIT FORMULAE - Potclays Which can be used to view or download a 2-page list of frits and their composition. Unfortunately for 2264 the entry is Composition not disclosed, which sounds like an intentional decision.
  20. Sorry to see that your enquiry isn't progressing. The glaze is crazing because it doesn't "fit" the body well. Which means that your friend needs to change at least one of: - the glaze - the clay body - the firing schedule If your friend posts details of these, preferably with a clear photo of the crazing, the experts here will have something to respond to.
  21. Tightening up on member location is a good idea, as some advice is location dependent. Can you fix the glitch where the string "Location" and member location run together, rather than being blank-separated? As in LocationBishops Stortford, UK Or if space is at a premium omit the word Location (iff one is given).
  22. Digitalfire's page on LOI has a graph of %decomposition vs temp https://digitalfire.com/glossary/loi
  23. As you have a background in materials ... Have you read Zachariasen's 1932 paper, sort of Pauling's bond theory meets glasses? https://pubs.acs.org/doi/abs/10.1021/ja01349a006 Richard Brow https://web.mst.edu/~brow/ used to host an interesting series of "student notes", I can only see a couple at the moment https://web.mst.edu/~brow/pdf_structure1.pdf https://web.mst.edu/~brow/pdf_structure2.pdf Segar's unity formula tries to capture some of this https://digitalfire.com/article/glaze+chemistry+basics+-+formula%2C+analysis%2C+mole%25%2C+unity%2C+loi ... but has severe limi
  24. Surprising find - Cone 6 horsehair raku (glazed inside and out) Not a solution to your question, but it ticks some of the boxes. AFAICS - glazes fired in a normal cone-6 firing, but prescribed matte outside glaze - 2nd firing to raku temperatures - greater danger of heat-shock - glaze is under the raku - cannot believe "smoke" clinging to a matte glaze is resistant to regular handling, let alone dishwasher-proof (ok for an ornament, maybe a water-filed vase?) - but it might be a better substrate for an exterior sealant, to stand at least regular handling and
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