Roast or calcine your Ravenscrag Slip (or other clays) for much better results

Monday 6th October 2014

insight-live.com/glossary/137">Calcined or roasted clays are indispensable in making many types of glazes, they reduce drying shrinkage (and thus cracking and crawling) compared to those made using raw clay. In a glaze, you can fine-tune a mix of raw and roast clay to achieve a compromise between dry hardness and low shrinkage.

This is Ravenscrag Slip, we roast it to 1000F (roasting is adequate to destroy plasticity and produces a smoother powder than calcining at higher temperatures). To make sure the heat penetrates for this size vessel I hold it for 2 hours at 1000F. Calcined koalin is getting harder to find, this same process can be used to make your own from a raw kaolin powder. One thing is worth noting: Weight lost on firing actually means that less of the roasted powder is needed to yield the same amount of material to the glaze melt, it can be anywhere from 5-12% less.

Pages that reference this post in the Digitalfire Reference Library:

GR10-A - Pure Ravenscrag Slip, GR6-A - Ravenscrag Cone 6 Clear Glossy Base, Ravenscrag Slip, Sterile white vs. pure Ravenscrag Slip as a liner glaze at cone 10R, Calcination

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.