The Chemistry of Designing Glazes for Pottery
In this article, I give a short introduction for the topic of designing glazes for pottery. There are several possibilities. You can collect recipes or formulas for glazes, or you can design your own by knowing what different ingredients do, and combining them in proportions that will produce the results you want.
I took a glaze calculation course in college. It was the fullblown technique, in which we learned what different ingredients would produce certain results. Obviously, adding cobalt to the glaze will make it blue, and if you add enough, it is a deep blue. Iron tends to make things red. Partly it depends on whether or not you allow oxygen in the firing process. Different ingredients will also do things like make a crackle appearance, determine whether it is a matte or shiny finish, and the like.
Our instructor taught pottery at Pima College, and he had developed a beautiful light blue glaze he used in much of his work. He was fun to work with, and he invited the students to his home several times. He was originally from Italy. He had personally developed some rather comprehensive information for stoneware, along with forms we could fill out that made it really easy to design a new glaze. I still have that information, and hope to get back to it someday.
We used stoneware in his class. We also were able to work in raku. Most people are familiar with stoneware, which is fired at high temperatures.
My pottery days and glaze calculation days predate the internet, but I just wanted to tell you about one of the most INTERESTING things I learned in college.
All photos by me.
Closeup of the Pot - in the introduction
This was a pot I made back then. It was hand built, and I was interested in exploring textures and shapes. I should have put a lot more glaze on it, since nearly all of it "burned off", so to speak. It's not my usual style of work, but it was fun to make.
I made several texture pieces. Some of them were 3 dimensional, and some were slabs with a texture on the surface, suitable for a wall hanging.
Raku is not as well known. The pot made of raku is fired to a high temperature, but the kiln is NOT allowed to cool down before it is opened. The pieces are taken out with tongs and put into ashes or something similar. The combination of the ash and the glaze that had been painted on the pot can produce some gorgeous iridescent colors. I was hoping to learn to calculate those glazes, but much to my regret, it didn't happen.
The clay body that is used to make raku has a couple of special characteristics. It is designed so it won't crack with sudden cooling. To make this possible, fired clay, called grog, is ground up and mixed with the other materials in the clay. The ground grog is rather rough on the hands, because it is something like having a clay body filled with sand. If you throw on a wheel with this, that is when it is most difficult for the skin. It can also be used for hand building of course. Hand building involves making slabs or coils and then gluing them together with slip, which is a very watery clay, that is spread on the surfaces to be glued together. The surfaces are than pressed together, and the slip glues them.
Raku was developed in Asia.
The piece in the photo has iridescent light blue and red highlights, with a southwestern motif. The gecko is a symbol of longevity and prosperity, and appears frequently in southwestern art. The design on the gecko's body is a traditional symbol for lightning. The artist is Jeremy Diller, and the piece is part of my personal collection.
Links to Glaze Calculators Online
These are online programs that you can use to design your own glazes. Each provides the necessary elements, and you specify how much of which, and it will also tell you if the glaze is workable for what you intend to use it for. I haven't tried any of them, so use them at your own risk.
Let me know of your experiences, or leave any other comments you wish.