Two glazes of the same chemistry: But supplied by different sets of materials

Saturday 25th June 2016

These two specimens are the same insight-live.com/glossary/88">terracotta clay fired at cone 03 in the same kiln. The glaze on the left combines 30% frit with five other materials. The one on the right mixes 90% frit with one other material (kaolin). Ulexite is the main source of boron in #1, it decomposes during firing expelling 30% of its weight as gases, mostly CO2, forming micro-bubbles. Each of the six materials in that recipe has its own melting characteristics, their interaction creates a non-homogeneous glass containing phase separations (discontinuities) that affect the fired surface. In the fritted glaze, by contrast, all the particles soften and melt in unison and produce no gas. Notice that it has also interacted with the body, fluxing and darkening it (thus forming a better interface). And it has passed (and healed) most of the bubbles from the body.

Pages that reference this post in the Digitalfire Reference Library:

Frit, Glaze melt fluidity comparison: Same chemistries, different recipes, Glaze Chemistry, Frit, Boron Frit, Phase Separation

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.