A reason for DIY underglazes: Commercial products don't adapt the medium

Wednesday 5th November 2014

All of these commercial underglaze colors. insight-live.com/glossary/92">Underglazes are not pure stains; they are a blend of stain powders with a host recipe (a ceramic medium, which is a porcelain-like mix of clay, frit, silica). But the recipe of that medium should be different for each stain type because they have different potencies, effects on rheology and influences on fired maturity. The stain/medium mix is supposed to mature enough to fuse to the body but not so much that it loses opacity, or worse, melts. And the recipe should be different for each temperature!

They all have a powder carrier; that is, they are suspended in a water/gum solution so they brush like paint and dry slowly. Suppliers have got the carrier working great. But the medium is a work in progress! Adapting or optimizing the medium recipe to each color is beyond the ability of most. It is so much easier to use one medium and the same percentage for each stain.

To demonstrate, I fired these...

to cone 8 in a melt flow tester. The blue, green and red are from one manufacturer. The pink/maroon one needs a lot less flux, the blue a little less and the green needs more. The black underglaze (D) has liquefied, gassed out and is about to head down the runway! The E black (a third manufacturer) has not even started to melt or even sinter. The black engobes were plastic; the colored ones were not (likely because a much lower stain percentage is needed).

Pages that reference this post in the Digitalfire Reference Library:

A reason for DIY underglazes: To better accept a clear dipping overglaze, A reason for DIY underglazes: Glass-bonding with the body instead of just seeking color, Underglaze, DIY Underglaze Development, Bleeding Colors

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.