The perfect storm of high surface tension and high LOI: Blisters.

Monday 8th April 2013

An example of how insight-live.com/material/173">calcium carbonate can cause blistering as it decomposes during a fast firing in our electric kiln. This is a cone 6 borosilicate glaze with 15% calcium carbonate added (there is no blistering without it). Calcium carbonate has a very high loss on ignition (LOI), and for this early-melting glaze, the gases of its decomposition are still escaping after melting begins. Another factor is also involved: Although the glaze has good melt fluidity, bubbles survived till near the end of the firing, resisting rupture (likely because of the high surface tension of the melt). When the bubbles finally did burst, there was inadequate time for healing to occur.

Pages that reference this post in the Digitalfire Reference Library:

Calcium Carbonate, Firing: What Happens to Ceramic Ware in a Firing Kiln, Two transparents having opposite melt fluidity/surface tension balances, Decomposition, Surface Tension, 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.