Why is this glaze so different on these two different porcelains?

Thursday 7th January 2016

Why the difference? The one on the right (Plainsman M370) is made from commodity American kaolins, ball clays, feldspars and bentonite. It looks pretty white-firing until you put it beside the Polar Ice on the left (made from NZ kaolin, VeeGum plasticizer and Nepheline Syenite as the flux). These are extremely low iron content materials. M370 contains low iron compared to a stoneware (less than 0.5%) that iron interacts with this glaze to really bring out the color (although it is a little thicker application that comes nowhere near explaining this huge difference). Many glazes do not look good on super-white porcelains for this reason.

Pages that reference this post in the Digitalfire Reference Database:

Copper Oxide Black, Copper Carbonate, Iron Oxide Red, Fe2O3, Porcelain

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.