|Monthly Tech-Tip |
This is a cone 10 glossy glaze. It should be crystal clear and smooth. But it contains strontium carbonate, talc and calcium carbonate. They produce gases as they decompose, if that gas needs to come out at the wrong time it turns the glaze into a Swiss cheeze of micro bubbles. One solution is to use non-gassing sources of MgO, SrO and CaO. Or, better, do a study to isolate which of these three materials is the problem and it might be possible to adjust the firing to accommodate it. Or, an adjustment could be make to the chemistry of the glaze such that the melting happened later and more vigorously (rather than earlier and more slowly). The latter is actually the likely cause, this glaze contains a small amount of boron frit. Boron melts very early so the glaze is likely already fluid while gases that normally escape before other cone 10 glazes even get started melting are being trapped by this one.
Questions and suggestions to help you reason out the real cause of ceramic glaze blistering and bubbling problems and work out a solution
Every glossy ceramic glaze is actually a base transparent with added opacifiers and colorants. So understand how to make a good transparent, then build other glazes on it.
Loss on Ignition is a number that appears on the data sheets of ceramic materials. It refers to the amount of weight the material loses as it decomposes to release water vapor and various gases during firing.