A secret to an ultra clear at low fire. Magnesia-alkali, low Si:Al ratio, more boron.

Thursday 27th October 2016

On the left is G2931J, a zinc alkali fluxed and high Si:Al ratio glaze. Those look like micro-bubbles but they are much more likely to be micro-crystals. High-zinc and high-silica is the mechanism for crystalline glazes, so it appears that is what they are. G2931K on the right has much more boron, double the Al2O3, less SiO2 and is magnesia-alkali instead of zinc-alkali. It is the product of dozens of tests to find an ultra-clear having a glassy smooth surface. This particular chemistry, although having only a 6:1 SiO2:Al2O3 ratio is ultra-gloss. In addition is has low expansion, will fast fire and the boron is not high enough to compromise the hardness.

Pages that reference this post in the Digitalfire Reference Database:

ZnO, G2931K - Low Fire Fritted Zero3 Transparent Glaze, Formula Ratios, Transparent Glazes, Glossy Glaze, Low Temperature Glaze Recipes

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.