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. Further, the ingredients used in glazes are seldom pure substances with constant composition and behavior.
Excluding a few exceptions, a typical glaze recipe brings together ingredients dug from the earth and which thereafter undergo minimal processing to clean and pulverize them. To keep costs down, suppliers use the least amount of processing consistent with adequate performance. Also, there are variations, time to time, in the composition of the material being mined. And, with some glaze components, there are several mines being worked at any given time.
As result, a specific glaze mix (with some exceptions, eg, tenmoku or temmoku) will yield different results, place to place, time to time.
But still, the idea of calculating a glaze design has merit, for two reasons:
- The chemistry of glazes can be simplified and hence readily grasped by the interested potter; and
- By starting with a known design (Seger formula) one can more easily fine-tune the mixture and more quickly make adjustments for irregularities in ingredients, in glaze/body interactions, and in kiln performance.