Here are some excerpts from the Primer. Print copies are for sale for $13.50 (including U.S. postage) from Hamilton Williams ClayWorks and, soon, from Amazon.com. Call 828-874-0190 to order, or mail a check to:

Hamilton Williams ClayWorks
116 Hauss Ridge Road SE
Valdese, NC 28690

A new edition of the Primer is on the way. New sections will include...

• The effects of changing silica and alumina levels in an established glaze.
• Mixing and glaze batch consistency tips.
• Glaze trouble-shooting.

Excerpts: Excerpt 1, Excerpt 2, Excerpt 3, Excerpt 4

Excerpt 1

Table of Contents

Introduction
1. Why bother learning glaze chemistry?
2. Oxides
3. An Overview of Glaze
4. The Oxide Groups
5. The Fluxing Oxides
6. What is the use of “calculating” a glaze?
7. Molecular Weight
8. Glaze Calculation, Step-by-Step
9. The Limit Formula
1010. Glaze Calculation Software
11. Development of Color
12. Opacity
13. Other Considerations
14. Resources
Appendix A: Weights of Atoms and Molecules
Appendix B: Expansion of Oxides
Appendix C: Unity Formulae of Common Glaze Materials
Appendix D: Experiments

Excerpt 2

"Introduction
Having been a professional potter for thirteen years or so, I can think of many occasions when my good humor, and perhaps even my sanity, smashed up against a glaze problem that I could not quickly solve. One instance several years ago occurred in late summer as I was rushing to fill pre-Christmas orders for shops and galleries while also getting ready for several shows. That time of year is our busiest, so it was with a little shock, and a mildly quesy feeling in the pit of my stomach, that I opened a kiln-load of pottery to find my two main glazes covered with pits, pinholes, and craters. These glazes were not only unattractive and unsellable, they were completely unsafe to use. I tried refiring a few pieces, but that only smoothed the smallest of the defects. While a few pots were salvageable, most of the firing went under the hammer. I did a little reading in my glaze texts, made a change or two, and fired another load of pottery confident that I had remedied the problem. The same thing happened, and another load of pottery fell under the hammer. Orders stopped going out, and I had to place some embarrassing calls to gallery owners explaining the problem. I did a little more research, made some new changes, fired another load. Again, most of the kiln load was no good. This went on for weeks. My mood darkened, my confidence slumped, and I began to seriously think of giving up pottery as a career. I finally discovered the source of my glaze problem after the better part of eight loads of pottery were ruined. The culprit was a new material I had started using a couple of months before. Once that material was removed from new glazes batches, things got back to normal, and I was able to complete orders and prepare for shows. The episode left a bit of a mark on my psyche, though.

During this period I delved into glaze chemistry like never before, desperate to find a solution for my problem. Even after the immediate issue was resolved, I realized it was only a matter of time before something like it happened again. My partial ignorance of the processes from which I made my living left me completely exposed to such occurrences. My livelihood was sitting on a house of cards. So I resolved to get better, to learn more. This became true of every aspect of my business: the clay, the glazes, the processes, the studio, and the business itself. This period is the point at which I changed from a slacker potter to a professional.

A few years later, I began teaching a glaze testing class at the local community college, which provided me the opportunity to organize all of the glaze knowledge I had accumulated along the way. It also forced me to delve even deeper in the subject so that I would be prepared to answer students’ questions. I sat down to organize my notes, and this glaze primer is the result.

For students and novice potters, glaze formulation can seem like a daunting body of knowledge. This primer is designed to introduce potters who have little or no glaze formulation experience with a basic understanding of the “how” and “why” of glazes. While this article assumes the reader has already advanced to mixing and using glazes from established recipes, little else is taken for granted. In addition to an explanation of glaze chemistry, this primer outlines several simple experiments that will give the reader first hand experience with glaze materials and their affect on color and texture in glaze."

Excerpt 3

"Calculating the formula for a glaze begins with using the molecular weight of each oxide to arrive at a comparative amount of each oxide in the fired glaze. This may sound confusing, but think of it the following way. To compare glazes, one wants to compare apples to apples, but a since all of the oxides have unique masses, or molecular weights, then trying to compare an unconverted percentage recipe is like trying to compare apples to oranges, or grapefruits, or even watermelons. By taking the molecular weight of each oxide into account, then all the different oxides (an entire basket of fruit) can be successfully compared in apple-to-apple terms.

So what is molecular weight? Looking at the periodic table, one finds each element has been assigned a specific mass. This mass, or “atomic weight,” has nothing to do with pounds or ounces, grams or kilograms. The “weight” of an atom is really an expression of its mass relative to the mass of Hydrogen. Hydrogen has been assigned an atomic weight of one (1) because it is the lightest element. All of the other elements were then assigned weights as multiples of the weight of Hydrogen. Oxygen, for example, has an atomic weight of 15.9998 because it is 15.9998 times heavier than Hydrogen."

Excerpt 4

"Even when a glaze is fully matured at the right temperature, opacity can be caused by a few other factors. The presence of tiny bubbles in the glaze can produce a opalescent effect, such as in a blue celadon. The presence of Phosphorus, contributed by bone ash, can produce this effect. Opalescence can also be produced by “a mixture of glasses of differing indexes of refraction.”3 Boron can encourage this quality in a glaze, producing a milky blue-white texture typical in rutile blue glazes. Solid crystals in the glaze, both tiny and large, can refract light and also create an opaque effect. Glazes rich in iron oxide, such as iron red or tenmoku, are an example of this effect. Some fluxing oxides -Calcium, Magnesium, and Barium- have an opacifying effect on a glaze if they are present in high enough concentrations. The opacity derived from all of these effects, though, can be driven out if the glaze if fired to a high enough temperature."

Excerpt 1, Excerpt 2, Excerpt 3, Excerpt 4