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About jpdes

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    British Columbia
  1. This is very useful information. Thanks for sharing, Marcia. What colorants were used on your "best test for the day" piece? Are the outlines a halo effect? Can you share the temperature and hold used? In a previous post you mentioned the Riggs' saggar firing schedule of 1650F with a 20 minute hold. Why go so high when such good coloration is achievable at lower temps?
  2. With apologies for inserting pragmatic queries into a mostly theoretical discussion, going back to your #8 comment, Neil, do you recall from your testing approximately what length of hold at cone 4 achieved cone 6 (and also the hold at cone 6 to achieve cone 8?). And what effect might firing to a lower temperature and holding to achieve the heat work associated with a higher cone have on an electric kiln? My theory is that, if done consistently, it may prolong element life but wear out relays faster (assuming they are not solid state). I have recently moved to ceramics from working with fused glass where heat work is a well developed and quantifiable concept as there is less variability in the chemistry of the materials. Firing as "low and slow" as possible is often preferred to maximize control and consistency of the end result. I'm curious about the transferability of this to ceramics.
  3. The basic recipe for molds for kiln-casting glass is 1 part silica to 1 part pottery plaster, by weight. Sometimes other additives are included for various purposes. Here's a link to get you started http://www.bullseyeglass.com/images/stories/bullseye/PDF/TipSheets/tipsheet_08.pdf See page 2 for the mold recipe. This mold formulation crumbles away from a glass casting after firing in the range of 1500 - 1600 degrees F. For your application, if the clay is already bisque fired there should not be an issue of it marring/adding texture to the surface. Supporting a bisque structure for machining is an interesting concept and piques my curiosity. Does the machining involve CNC?
  4. Strike firing glazes is an interesting concept. Glazenerd, do your time/temperature descriptions refer to an eg. 30 minute hold at 1350F on the cool down from a glaze firing or an entirely separate firing starting with cold, glazed ware? Would it matter which approach was used?
  5. There's an amazing amount of information in this thread. Thanks so much. Further to the rate of firing/slow cooling concept, I have been surprised at the amount of glaze alteration that can occur on refiring Cone 6 glaze fired ware to lower temperatures. For example to mature china paint or attach decals. I have seen noticeable permanent visual change in glazes when refired to as low as 1450F which must be below glaze softening temperature. This has been most noticeable in titania containing glazes. (Thank you Joseph for alerting me to that.) To guide exploration of glaze manipulation at such very low temperatures I'm interested in further information and concepts regarding Lowest temperatures at which permanent glaze appearance alterations can occur? Glaze ingredients and combinations which may react at these lower temperatures?
  6. The modifier glaze effects are dramatic. Are you willing to share more about its composition?
  7. Thanks for the replies. US Pigment's reputation clearly supports trying their proprietary products. The images I've seen of Marcia Jestaedt's work are impressive and the description of the process on her website is very interesting. I've successfully used low fire glazes for raku but the silver nitrate wash takes it to a new level - at least when applied by expert hands.
  8. Has anyone used, and are willing to comment, on US pigment encapsulated stains and raku glazes? I'm wondering how they compare to comparable products from other companies.
  9. How close together/dense should the coils be so that the bottom is sufficiently supported and does not distort on the glaze firing (for a mid fire stoneware clay)? Should the coils be kiln-washed to prevent sticking?
  10. Most glass kilns are rated to only 1700 degrees F (cone 08/09) and not intended to hold close to that temperature for extended times.
  11. Certainly some helpful suggestions, thank you. I went back and reviewed discussions about the soda wash described by Chris Campbell. Does this flux to an extent it would result in sticking to a shelf if used on the bottom of a piece in a cone 6 firing? And a similar question with underglazes as, in my experience, some flux to a certain degree. If using underglazes on the bottom/against the shelf should one be attentive to choosing those that fire to a matte finish?
  12. I make slab built platters and shallow bowls using cone 6 clay and glazes. I like a flat bottom, no foot look but not the resulting large expanse of bare clay on the bottom of the piece. I am wondering whether spraying the unglazed bottom with a solid coating of a solution of clear frit would enhance the aesthetics and long term functionality. The frit solution would be applied after the final glaze firing. I am thinking of using a solution of Ferro Frit 3124 or 3134. The pieces would then be fired upside down (glazed surface against the shelf) to the melting temperature of the frit which would be in the range of 1450 - 1600 degrees F (cone 016 - 012). I am thinking the cone 5-6 glaze would not soften at these temperatures so the glazed areas against the shelf should not be a concern. It would require an additional firing so obviously not feasible for production pottery but would it make sense for low volume decorative pieces?
  13. Thanks Marcia. I'll track down those I am not yet familiar with. Having been enlightened by many of your responses on the forum I look forward to your dvd.
  14. Thanks for the safety warnings. I assure you safety of person and property will get full and proper attention at all times.
  15. Thanks for the thoughtful replies. I thought that might be the case. Can anyone suggest a book or reference source that gives a technical description of raku glaze behavior ie. at what temperatures various reactions occur, how rapidly does cooling have to happen to maximize color effects, etc.? So far I've mostly come across the "do it this way" descriptions.
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