What is a Glaze?

Q: What is a glaze?

A: In plain terms, a glaze is a very thin layer of glass formed on a clay pot during the firing processes, that is, during one of the times that the fragile clay vessel is heated to a high temperature (above 1800° F, 1000° C).

Are Glass and Glaze the Same?

Q: Are glass and glaze the same?

A: Sometimes, but not often. Glass itself dates back at least 50 centuries. Mix sand and some other dry minerals, heat in a fireplace, and you obtain a material often called a “network polymer” (a “mer” is a unit molecule and “poly” means many, joined together).

What Affects a Glaze Surface?

Q: What affects a glaze surface?

A: A glaze surface may be glossy, satiny, or rough (dry matt); the actual result will revolve around the silicon oxide and the alumina oxide contents, both in relative and absolute terms. A glass that contains 60% silicon oxide (silica, flint, quartz), plus or minus 5%, will usually make a good glaze.

How Many Materials are there in a Glaze?

Q: How many materials are there in a glaze?

A: If one examines many glaze recipes, one soon realizes that most of them contain ten ingredients, or less. These, in turn, are used repeatedly in different recipes for a given firing range (low-fire, mid-fire, or high—fire).

What Factors Go Into a Glaze?

Q: What factors go into a glaze?

A: Glaze design is both simple and complex; the list of basic oxides can be expressed in simple chemical terms, but the interaction of the usual ingredients (up to 10) is most difficult to describe and even more difficult to predict with confidence.

How Do You Design a New Glaze?

Q: How do you design a new glaze?

A: It may sound like magic but to design a new glaze successfully requires no mysterious chants, just a thorough understanding the factors involved in the process. There are two main ways to develop a new glaze:

  1. Choose suitable raw materials (mostly those that have worked before) and mix them in various proportions to meet a planned series of glaze tests; or
  2. Choose an appropriate “formula”, based on previous experiments, and derive a “mix-batch” recipe for testing, etc.

What is a Seger/Unity Formula?

Q: What is a Seger/Unity formula?

A: One way to help evaluate a glaze recipe is through the Seger or Unity Formula named after Hermann Seger who a century ago arranged glaze components into a particular order. He called one group the “flux” oxides—usually the oxides of Lithium, Sodium, Potassium, Magnesium, Calcium, Strontium, Barium and sometimes Iron.

What’s New in Glaze Design?

Q: What’s new in glaze design?

A: With the advent of the home computer, doing a glaze design no longer involves lengthy, tedious calculations by hand. Nowadays, any potter can undertake glaze design providing she/he has:

  1. Access to a microcomputer, either an IBM type with a disk operating system (DOS) or an Apple “Macintosh” type with its “pull-down” menus; and
  2. Access to specialized computer programs that simplify glaze calculation and analysis.