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Norm Stuart

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  1. That's exactly why Gerstley Borate is the ideal base ingredient for a glaze. There's very little that needs to be added to make a complete glaze. How much bentonite do you use with Gillespie Borate frit?
  2. Typically when I've bought colored COE 96 soft glass to use on ceramics it has come in the form of a ground frit, so mixing this with another frit is not a big problem. If you're using marbles or some other glass shapes in the bottom of a bowl I'd weight out an equal amount of Ferro 3110 to sprinkle around where I placed the marbles. This plate with Duck a l'Orange has COE 96 glass inside a porcelain orange slice, which has shivered creating the illusion of orange cells, with the same COE 96 glass mixed with Ferro 3110 frit as an orange sauce, which fits the previously fired Cone 6 Majoli
  3. I've always used the rule: if my tongue sticks to the ware, then it's dry enough to bisque. I use a pre-heat on glazed items in lieu of licking each one.
  4. I'd suggest reading "Mastering Cone 6 Glazes" regarding the need to test glazes for leeching. This spreadsheet has the Food Safe Clear Liner Glaze they use as an example. http://home.roadrunner.com/~nstuart/MC6G.xls
  5. I'm sure every manufacturer knows their product best. With our Cress e-23 we leave the top peephole unpugged with the lid closed. I don't even prop the lid open for pre-heats, as the steam and moisture seem to have no problem escaping with the lid closed. The only exception to this is when we're doing a gilding firing where we leave the lid propped-open until around 500 F to let the volatile and toxic fumes escape, per the instructions on gilding material. When we previously used a very much older Cress kiln of the same size, but with 24 amps instead of 36, someone in our studio
  6. Watercolor Green and Blue have no clay in their recipe, so would sink to the bottom like a stone, so the recipe tells you to add 3.1% bentonite which is a highly suspending silica clay. Unfortunately, different types of bentonite all have different abilities to suspend. So if you added 3.1% VeeGum you now have a glaze which is too flocculated holding too much water. So in retrospect you need less bentonite. I have this problem with all of Steven Hill's recipes, so he obviously uses a less suspending bentonite. However, fire a test tile with what you currently have because this glaze
  7. Once you work Epsom Salts or Calcium Chloride into a hard-panned glaze it should stay suspended. If it starts settling too quickly it either needs more of the above or it needs bentonite for the Magnesium Sulfate or Calcium Chloride to act on.
  8. The beads you're working with are most likely Soft Glass which has a COE (coefficient of expansion) around 2.44 which is well below that of clay which typically ranges between 4.6 to 8.0 which is why the glass is shivering. To help the glass better fit the clay, place it with a high expansion frit like Ferro 3110 (coe 10.1)or Ferro 5301 (coe 11.4). Hard glass has an even lower COE so would create more fit problems.
  9. Avoiding harmful materials would be terrific. Unfortunately everyone involved in ceramics use many materials which are harmful to people. So we have to settle for using potentially harmful materials in a safe manner. At the top of the list there's silica and high silica materials, followed by most heavy metal colorant oxides/carbonates. Cobalt, chrome, copper, nickel, manganese and exotic metals - all toxic. We have respirators for dust or organic solvents - and washing / settling tanks to capture the heavy metals. I'm impressed to see everyone jump up out of their chairs to
  10. We're human so mistakes are inevitable. I think my primary mission is to prevent the backyard behind my Optometrist's office, our ceramic studio, from becoming an EPA Superfund site.
  11. I just naively found a substitution of one for one which seems to "~double" the amount of fluxing action. Laguna lists Lithium Fluoride as "somewhat" more fluxy than Lithium Carbonate. Lithium Carbonate is about 18.93% Lithium by weight - 40.74% Li2O and 59.25% Carbon Dioxide. Lithium Fluoride is 26.76% Lithium by weight, but the Lithium Fluoride does not break-down into Lithium and Fluorine at kiln temperatures - so the lithium is not fully available as a flux. But the Fluorine also acts as a flux so somehow the net effect is more fluxing action and a slightly different fluxing action.
  12. Your skill-set and presence as a teacher probably heads off a lot of potential problems before they end up in the kiln. I'm only infrequently at our studio and I rarely load our kiln, so have procedures and material selection set in place to try to minimize the effects of our inevitable worst case scenarios. I teach ceramic chemistry to those who are interested when I'm there, but the primary model in our studio tends to be learning by doing. Even with occasional incidents, I think this is a better learning environment for people than our studio's previous model where two experts
  13. John - your skill set is far too advanced. Mere mortals deal with problems which might horrify you - like people who use a shrink ruler to measure the distance a thermocouple extends into a kiln. When you run a studio filled with amateurs who apply far too much glaze you need to use a kiln wash of 50% alumina hydrate and 50% kaolin. The problem with using a kiln wash of Silica instead of Alumina is free-running glaze enables the silica to join the glaze melt. The result is you use a hammer and chisel to remove the glaze rather than simply lifting the ware and attached glaze run off
  14. I've made so many glazes now that I recognize glazes even when the name is changed. Like the macro-crystalline glaze Babs was trying out. There really is nothing new under the sun. Knowing the history of a glaze is helpful - like Pete Pinnell's "Weathered Bronze Green", which was a Cone 10 glaze which one of his students discovered "worked" at Cone 6 as well. I was able to make this glaze far more reliable by replacing lithium carbonate with lithium fluoride, because a cone 10 glaze fired at cone 6 is merely missing enough reliable flux. The quick melting of frits, even though they'r
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