Monday, December 29, 2008
Studio Day - Glaze Mixing
I would like to share with you who are interested the process of ceramics. I am going to start today with the end of the process -- that would be glazing. I have a lot of once-fired pieces which need to be glazed, and I need to get that done before I allow myself to fill up the studio again with freshly thrown ware. I also have several tiles which need to be glazed. One is for a gift from one of our guests to another of our guests, and others are for my Ovarian Cancer Art Project.
So today I started by mixing two different glazes. One glaze is for plates and dishes. It is a very specific glaze in that it allows for bright blues when mixed with cobalt and soft celedon when mixed with copper. This is one of my standard glazes, anyone who has seen my pieces knows that these are two colors I work with a lot. The second is the running glassy glaze for my art tiles, which is colored with copper to a bright turquoise or with iron for a transparent amber color. This time I am going to do an experiment also by mixing chrome with this glaze to see what kind of green I get.
Before I go any further, let me explain something. I work almost exclusively with high fire, stoneware glazes when creating my work. The only time I work with low fire glazes is when I am making ceramic tiles for mosaics. The difference between high fire and low fire is very clear. Low fire pieces can be more colorful, but the glaze stays on the surface of the clay. Low fire pieces chip easily. Low fire pieces sweat when water is placed in them. In contrast, high fire pieces are not as bright in terms of color, but the glaze surface molts with the clay body, forming one structure. In other words, the clay vitrifies -- becomes glass like-- and many, many times more durable than low fire pieces. They are freezer, microwave, and oven safe. For me, they are "real" ceramics because they are completely functional. That's why they are known as stone ware.
So I am going to take you through the glazing process. It's very unromantic.
Every ceramic glaze contains three basic components - something to make it flow when it heats up, something to make glass, and something to brake the flow process. If these three things are not in balance, the result is disaster. These three components need to be chemically calculated, and then translated into exactly how much of each raw material needs to be mixed to get the desired results. A million things can go wrong. Some raw materials hate cobalt, some hate iron, you have to know what works with what, and then do the calculations to make as sure as possible that the glaze will work.
Then, you must measure, with an accuracy of a within a tenth of a gram, the raw materials and mix them together.
Sometimes the raw materials clump up and have to be ground up with a glass grinder. If the clumps are too big, I have an electric mill which I can use to ground up the raw materials.
Today I mixed two 1-kilo batches of glazes and tomorrow I will mix up two more.
The next step will be to add water to the glazes - the will need to go through a double-fine glaze strainer. The process of mixing up large quantities of glazes with water takes time, because of the straining. Then, I will glaze the pieces. That will be another blog post.
Together, you and I will fill the oven, and open it up to see how the piece have come out. Here are some of the pieces which will go into the oven for the next glaze firing:
And lastly, the view from my studio when I closed up this evening.