Cone 2: The real difference between terra cottas and white bodies

Friday 19th July 2013

The terra cotta (red earthenware) body on the upper left is melting; it is way past zero water absorption, past insight-live.com/glossary/95">vitrification. The red one below it and the third one down on the right have 1% absorption (like a stoneware), they are still fairly stable at cone 2. The two at the bottom have higher iron content and are also 1% absorption. By contrast, the buff and white bodies have 10%+ absorptions. Terra cotta bodies do not just have high iron content to fire them red; they also have high flux content (e.g. sodium and potassium-bearing minerals) that vitrifies them at low temperatures. White-burning bodies are white because they are purer (not only lacking the iron but also the fluxes). The upper right? Barnard slip. It has really high iron but has less flux than the terra cottas (having about 3% absorption).

Pages that reference this post in the Digitalfire Reference Library:

Firing: What Happens to Ceramic Ware in a Firing Kiln, Terra Cotta, Clay Body Porosity, Maturity, Earthenware

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.