Orange-peel or pebbly glaze surface. Why?

Sunday 14th June 2015

This is a cone 10 glossy glaze. It has the insight-live.com/glossary/118">chemistry that suggests it should be crystal clear and smooth. But there are multiple issues with the materials supplying that chemistry: Strontium carbonate, talc and calcium carbonate. Each has a significant LOI and produces gases decomposition. When the gases need to come out at the wrong time it turns the glaze into a Swiss cheeze of micro-bubbles. A study to isolate which of these three materials is the problem might make it possible to adjust the firing to accommodate it. But probably not. The most obvious solution is to just use non-gassing sources MgO, SrO, CaO and BaO (which will require some calculation). There is a good reason to do this: The glaze contains some boron frit, that is likely kick-starting melting much earlier than a standard raw-material-only cone 10 glaze. That fluid melt may not only be trapping gases from the body but creating a perfect environment to trap all the bubbles coming out of those carbonates and talc. All of this being said, a drop and hold firing schedule could also smooth it out a lot.

Pages that reference this post in the Digitalfire Reference Library:

Strontium Carbonate, Talc, Calcium Carbonate, Orange Peel Surface, LOI, Glaze Blisters

This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.