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Norm Stuart

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Everything posted by Norm Stuart

  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 Majolica glaze.
  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 got it into their head that "all dampers have to be open for an oxidation firing". Of course he was reading about gas kilns, but to him this meant both peephole plugs had to be open. With both peepholes open the Cone 6 firing timed-out and never reached anywhere close to Cone 6 as the heat loss from both peepholes being open was greater than the heat the kiln could generate.
  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 is very fluid. If you find a way to apply it too thickly, you'll have a puddle of glaze. You can deflocculate the glaze with Darvan, Sodium Silicate, or Sodium Carbonate, but this will not eliminate the excess water - unfortunately that you have to pour-off after it's settled (which is unlikely to happen with bentonite) or evaporate the excess water, or add more of the glazes's other ingredients without adding more bentonite. We use VeeGum and as a result I always suspect any glaze recipe which calls for more than 2% bentonite. You can always add additional bentonite to the glaze after it is mixed up. The way to do this is add bentonite to a cup of boiling water and mix it with a stick blender.
  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 intervene when a new person decides to wash out their brush or container with the hose into the garden "because they don't want to put their hands into the dirty water" in the settling tank. Most glazes at our studio are safe once fired, but are poisonous to drink - and most recipes are made with ingredients which are more dangerous to breath when you're are measuring them out and mixing them, than if you drank them as a liquid glaze.
  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. Once you use LiF or fluorine frits like Ferro 3269 or Ferro 5301, you'll soon recognize that particular look which is being contributed by the fluorine. It's subtle but obvious - more crystal formation and slightly more white threads in a matte glaze like Weathered Bronze Green.
  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 did everything and no one else at the studio was allowed to learn how to fire a kiln, make a glaze, or participate any number of other things. Maybe I'm just lazy - being unpaid can lead to that sort of perspective. Three weeks ago may partner ran over and stopped a kiln fire during the pre-heat because in talking with me he realized that the person he had loaded the kiln with had applied a bottle of polymethacrylate plastic and water as "kiln wash". It was on the same shelf as the kiln wash, but was clearly labeled polymethacrylate. You'd never believe what goes on at our studio.
  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 the shelf. Even when this doesn't happen, some glazes like the copper heavy Philadelphia Green glaze mist onto the shelves around them. With an alumina hydrate kiln wash you don't even really notice this - but with a silica based kiln wash, repeated firings with misting glazes without reapplying new kiln wash will build up a gloss on the top of the silica based kiln wash. Your analysis of the refractory nature of silica combined with kaolin is wholly accurate if you fire an empty kiln without ware. The glaze on the ware begin to contribute a wide variety of fluxes to the silica kiln wash, and added flux change silica and kaolin from a refractory to a glaze. For most of us, alumina is a gift from the gods.
  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're chemically identical, will create a different look at cone 6. These two chemically identical Butterscotch recipes show that. The frit version at Cone 6 is much glassier. If you do a lot of Currie Grids you'd discover "Dry Pumpkin" which is just a slight variation in the percentage of several of the ingredients, with the Red Iron Oxide removed. Yet if you were trying to use these glazes as a basis to replicate this Bailey Shino, you'd fail because the underlying chemistry is completely different even though there's a certain similarity in the overall look of the glaze.
  15. The person who previously used your shelves almost assuredly used a kiln wash of 50% Silica and 50% Kaolin. If you use 50% Alumina Hydrate and 50% Kaolin you don't end up with these problems. http://jeffcampana.com/self-leveling-kiln-wash/ The shelves should be ground down, but it's a huge messy job. In the interim, you can apply a fairly thick layer of kiln wash like Jeff Campana's to avoid your ware sticking to the glaze, but it's not going to make the shelves level.
  16. I've found only two widely popular glazes designed for a rapid free-fall in temperature after a Cone-fire to ^6 in an electric kiln, which I've not been able to reformulate to our six hour slow-cool between 1,800 and 1,500 F. The first is Laguna Tang Lime Crackle, a combination of Ferro Frit 3269, 1/2% Chrome Oxide, and some silica. Instead of crazing with a clear lime glass, it becomes and uncrazed mustard color when cooled very slowly - as the slow-cooling fixes the glaze-fir problem designed into this glaze. The second widely used glaze are the many variations of Blue Hare's fur glaze. The rutile in this Nepheleine Syenite doesn't leave hair-like trails in the nepheleine glass melt, but becomes a uniform blue color, regardless of the recipe tried. In general Nepheleine Syenite heavy recipes need a different flux for slow-cooling as the high Alumina content of this material tends to provide a sold coloration when given enough time to react and crystallize. Enough time has passed that no one at our studio even remembers these glazes, which is fine, but reformulating them is still a goal of mine. Our studio members voted that they preferred the slowest-cool program we tried out rather than the faster slow-cool suggested by the book "Mastering Cone 6 Glazes". In general with very slow cooling you end up with a more sophisticated cone 10 style look without the bright glassy "poster paint" look typical of many Cone 6 glazes in free-fall cooling. These two glazes below illustrate the sort of difference very slow-cooling has on some glazes. I much prefer Randy McCalls Warm Jade slow-cooled to the original. I needed to add 10% extra frit to develop a nice glaze from Clear Blue which becomes over-crystalllized. Some people prefer the more crystallized look of a slow-cool, while others dislike it. The consensus at our studio is members like the look of the very slow-cooled glazed. The difference in look between fast-cooled and slow-cooled is quite distinctive. Which look you want for your ware is an entirely personal choice. As with the last glaze shown, over-crystallization has to be dealt with by adjusting the glaze recipe.
  17. John -- Anything you wold change with my "thick pieces bisque" before I use it next week? F/Hr F Hold 1 RAMP 60 200 8 hours 2 RAMP 100 350 3 RAMP 350 950 4 RAMP 100 1,000 5 RAMP 50 1,150 6 RAMP 400 1,638 7 RAMP 108 1,888 30 Minutes 8 RAMP 400 1,100 9 RAMP 200 1,400
  18. I'd like to tell all high school and other teachers that when you run into an extremely gifted art student, particularly those without tuition and board money to pursue their four year degree in Art, Music, or Theater -- to be certain they know to apply to CalArts and their best of the best arts programs. I sponsored a earnest and talented self-taught musician. In spite of not being able to read music and having worked as a waiter for five years after high school - he ended up going tuition free with his housing and food and spending money provided as a scholarship. A tremendous opportunity for the right person. You have to love your art more than anything else. It's a quiet and residential campus, near Magic Mountain north of Los Angeles, with state of the art everything and strong ties to entertainment industry firms. http://calarts.edu/ The student's art portfolio and personal interview trumps pretty much everything else, as they understand exceptional artists may not have had the desire to become A students in other subjects.
  19. Benzine -- Thanks SO much for the tip about using Acrylic Copolymers as a "Ceramic Enhancer"! Adding a little Zaino Car Wax to clay is incredible. I addition to starting with the three copolymer formula like ceramic enhancer, they add Siloxane - a hydrocarbon soluble silicone friction reducer which helps application and removal of the "wax" - actually a three monomer plastic. The Half&Half Laguna clay quickly deflocculates and becomed extremely plastic - little force is needs to deform the clay-slip and it becomes very cohesive with the ability to bond heartily to dry clay other peices - drying absolutely hard. The copoymers burn out at 350F leaving the intermeshed clay, from being deflocculated to sinter together on their own. I'm going to look locally for the most inexpensive Actrylic Copolymer floor wax in a smaller container. I don't think I'll be working with straight clay anymore. But I can imagine situations where I'd also add bentonite and some frit for flux for repairs, but I'll wait and see. As a protective covering, copolymer plastics are extremely resistant to detergents and bacterial action, but offer little protection from acid attack - so adding acid, say to change flocculation, would be contraindicated. In terms of car wax, this means bird excrement which is extremely acidic needs to be removed quickly and additional copolymer wax applied. The alternative is to apply alternate layers of copolymer wax and carnuba wax (which is acid resistant). So far, it doesn't look like ceramic enhancer is less than double the price of comparable floor wax, so perhaps they dilute the wax with water before selling it as ceramic enhancer.
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