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Min

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  1. Could probably rework the recipes using a strontium frit in place of the strontium carb, would have far less off gassing / pinholes that way.
  2. From my scrap kiln shelves pile, a couple Corelites warped, 20" square. All of them warped. Glad yours haven't warped, maybe something with the size of the shelves?
  3. @LeeU and @oldlady, click on the banner that Jennifer posted at the top of the forum, it gives some details. This isn't going to be like the big change that happened a couple years ago, more along the lines of updates. Think of it like a tuneup for your car, necessary to keep things running smoothly.
  4. If Tom's engobe recipe isn't a fit then another one that would be worth trying is one I got from George Vardy, a tech for Mason Colour Works (Mason stains company). I'm pasting an email he sent me a few years back. If you can't get VeeGum T then I would sub with macaloid (bentone ma) if you can get that or if not then bentonite. In place of the stain use zircopax. Doubt you would need the 40 parts, I would mix up the base, with the bentonite, then try 10 parts zircopax, brush / spray it on a test piece then add another 10 parts zircopax and repeat process up to the 40 parts. "One of the best engobe formulas is a very simple one, developed years ago by Ron Mason who then owned Mason Color Works, Inc. Carol Mason, his daughter, now operates MCW. EPK Kaolin 10 parts Feldspar. 25 parts Flint. 25 parts Stain. 40 parts Mix well with water, add 1 part VeeGum T that has been FULLY broken down in water, screen thro 100 or finer screen, bring to your painting consistency by addition of more water if needed. When using very strong stains such as cobalt blues or chrome greens you may need to reduce the amount of stain if the fired color is too strong for your requirements. This can be used to decorate on clay or bisque. Be sure to dry fully before glazing."
  5. The clay COE figures that some companies put out are likely in the ballpark but the validity of the figure is dependent of firing conditions. If you have a base glaze recipe that you can change the proportions of, without adding another flux, to get a few versions of it to go from low to high expansion then try them out on the clay with no engobe. One variable at a time. Glaze COE figures get you in the ballpark but if you use dissimilar recipes, ie different fluxes, both having the same COE it doesn't mean they both will fit. Some fluxes give more of a "stretch" to glazes than others, others don't work in a linear fashion, like boron for example. The clays I use don't come with COE figures either.
  6. COE figures from glaze calc software, like Insight, don't work for some glazes, all slips and all claybodies. COE figures for glazes are useful when all materials in the glaze have melted into a glassy matrix. Crystalline glazes, including microcrystalline, have some materials that have precipitated out of the glassy matrix therefore are not part of the complete melt resulting in COE figures that won't be accurate. Slips and claybodies are on the extreme end of this principle. Shrinkage is just that, how much a clay shrinks during drying and firing, COE is the distance any material expands per unit of length upon heating one degree of temperature. COE is reversible as on cooling there will be contraction.
  7. The slip is shrinking more than the bisque you put it on. Engobes have lower shrinkage than slips and can be formulated to go on dry, leatherhard or bisque. Daniel Rhodes engobe recipes here.
  8. To me that upper band looks like the same as what's on the inside of the bowl and looks like a magnesium matte glaze like this one. To answer your question about engobes, Daniel Rhodes engobe recipes for leatherhard, bone dry or bisque for low, mid and high fire, part way down this book preview, from Glazes for the Self Reliant Potter by Daniel Rhodes.
  9. Hi wavesofwoodenlegs and welcome to the forum. I wouldn't expect this to work. From the FDA re edible glitter ingredients: "Common ingredients in edible glitter or dust include sugar, acacia (gum arabic), maltodextrin, cornstarch, and color additives specifically approved for food use, including mica-based pearlescent pigments and FD&C colors such as FD&C Blue No. 1." The only thing that wouldn't melt out (at low temperatures) would be the mica. Mica is used to get a sparkly effect in some lowfire claybodies. Would be an expensive way to get that effect and the particles of mica in the edible glitter are going to be tiny. That being said it's always fun to try out different off the wall things, results are not always what you expect but can be interesting. edit: gold lustre from Duncan.
  10. Absolutely you could add a candle / preheat. (all in F) Ramp 1- 60 / 200 / hold as long as you need to. (put a piece of glass above an open peephole, if it steams up then pots aren't dry enough yet) Ramp 2 - 320 / 1020 / 0 hold Ramp 3 - 153 / 1112 / 0 hold Ramp 4 - 180 / 1837 / 0 hold Ramp 5- 108 / 1950 / 0 hold BTW a quick and somewhat safe way to check if your pots are dry is put a bone dry one up to your cheek. Now put one you aren't sure about on your cheek, if it feels cooler its not dry. If in doubt candle (preheat), it's fine going for longer than a 2 hour candle, especially if the pots are more than 1/4" or so thick. Doesn't add much cost to the firing. For fairly "clean" white clays the sentry program will be fine but if you are firing "dirty" clays, ie dark coloured clays then I would suggest a different schedule to allow more of the impurities in the clay time to burn off.
  11. Hi Giggles and welcome. Are you looking for a commercial glaze or a recipe? Oxidation? Dark clay or light? Opaque white, gloss? I would strongly suggest making up some test tiles with the same texture on them to try out any possible glazes before committing your salad bowl.
  12. Taken from the manual for the Sentry 2.0 controller. I would just take the schedule and change it to from 4 to 5 ramps, add an early inconsequential one, something like 100F / 100F / 0 hold then just get rid of the 4's and round up or down. ramp 2 - 320 / 1020 / 0 hold. ramp 3 - 153 / 1112 / 0 hold. ramp 4 - 180 / 1837 / 0 hold. ramp 5- 108 / 1950 / 0 hold. The 4th ramp should come up when you start entering the program if you enter a 5 ramp schedule. My test kiln has a sticky button too.
  13. Larry, it would really help if you would you post a picture of the crack(s) plus if you would split one in half so we can see the cross section.
  14. @Lbegley, a tiny bit of copper carbonate added to brushing medium stops the gums in the brushing medium from rotting, magma glaze additive suggests using copper also. The amount used is so small that it doesn't effect the colour. Same principle would apply to underglazes as glazes. By weight it would be 0.04% copper carbonate, like everything ceramics, if you try this test a small amount first.
  15. If the plastic bags were fairly sealed up any condensation that might have formed within the bags would be trapped and then drip back down onto the platter. I think this could cause water splitting the clay. Silty clay seems more prone to this. Since clay cracks are a result of a stress put on the pot I would be looking at even drying, be it fast or slow.
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