Can a glaze act as a sealant? Yes. But only if it fits.

Friday 10th April 2015

Left: Plainsman M340 fired to cone 6 where it achieves good density (about 2% insight-live.com/glossary/72">porosity) and excellent strength. Fire it to 1% porosity and it will bloat and warp. So cone 6 is its practical optimal temperature. Being able to measure the 2% porosity demonstrates water penetration, albeit slow penetration. So glazes must fit to seal the surface.

Right: H550, a Plainsman body intended to mature at cone 10, but fired to cone 6 using the same glaze. The clay is much more porous. The piece was dropped and cracked (the crack runs diagonally down from the rim). It was then dipped into water for a few moments. Immediately the water penetrated and began to soak into the body (spreading out from the crack). If this glaze were to craze, the entire thing would be waterlogged in minutes. But it doesn’t craze. So, the piece would be usable (with a sealed foot ring of course).

Pages that reference this post in the Digitalfire Reference Library:

Glaze fit, Maturity, Functional

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.