"Glaze" as a Generic Term
To understand the roots of the confusion, it is easiest if we understand the word we potters share with our friends, the painters. Glaze and glass come from the same linguistic roots. These words are old, and as such have multiple definitions.
A glaze, as a generic term, is a thin, transparent covering. It can refer to ice covering tree limbs after a freezing rain, a thin transparent layer of painting medium on a canvas, the glass pane covering a window opening in a wall, as well as our own dear ceramic glazes covering the clay body of a pot.
Painterly Glazing
Painters working in a variety of media such as acrylics, oils, and watercolor often use a technique called "glazing". In painting glazes, thin transparent layers of either clear or slightly colored extender or painting medium are built up on top of an opaque ground layer.
Many products are on the market and can be found at art supply and art and craft stores that are labeled as "glazing medium" or list "glazing" as one of the techniques they can be used for. While true, these products are for painters.
When in doubt, find a customer service person and ask!
What Could Happen?
Don't mistakenly use painting glaze mediums or extenders in underglazing or glazing pottery. Problems that can occur include:
- Crawling -- Glaze mediums form a thin skin of paint medium on the surface of the pottery piece. This does not allow the glaze to properly adhere to the clay body's surface, which will result in crawling.
- Pinholing -- Since painting glaze mediums and extenders are not specifically made for pottery, it will have chemicals that will burn out unpredictably, which might be a cause of the pinholing.
- Also, it is possible that chemicals will be introduced into the glaze matrix which could cause problems which cloudiness (a little calcium goes a long way) or other unexpected results.