Creating crystalline glazes

In the afternoons Isak Isaksson works with glazes, the most intellectual of the elements in the creation of a ceramic object. A great interest in chemistry is the basis for research into how different components react together on different types of clay, in different types of firings with or without air supply – and during different cooling rates. In contrast to the continuous work with classic vessel shapes, the crystal glazes are a field for constant experimentation for Isak Isaksson: “The crystalline glazes are a world of their own, infinite. The possibilities for variation are breathtaking. Every time I try or discover something new, new opportunities and ideas open up in my mind.”

Isak Isaksson has been experimenting with crystalline glazes for almost 40 years and now has thousands of glaze recipes collected in a database. To find out how much of each substance should be included in a specific glaze mixture, Isaksson uses a glaze calculation program. “The program is static and generates very standard glazes as standard. But if I shift the balance of subjects in any direction, things happen. The program keeps track of all the substances’ atomic mass and calculates based on these,” describes Isaksson. The program is based on the atomic weight section of substances, but the actual atomic weight can vary between different refractions and geographical locations and thus lead to surprises during firing. The base of the glaze is a so-called frit, or glass mass, which Isaksson mixes himself or buys ready-made in powder form. Frits are prepared by melting specific elements in special ovens, adding water, drying and grinding to a fine powder. There are lots of developers and manufacturers of frits for, among other things, the tile and porcelain industry. Each frit has an international designation, for example “Ferro Frit 3289”. The quality of the frit has a great influence on the smoothness and regularity of the glaze and also on the color, luster and clarity.

The actual color scheme of the glaze is described by Isaksson as relatively uncomplicated until you start to have several oxides in the glaze. If Isaksson has 3% cobalt oxide in a glaze to get dark blue, the melting temperature is raised by 4 degrees. 4% iron oxide in the glaze, on the other hand, lowers the melting temperature by 3 degrees. Most glazes melt between 1000 and 1300 degrees Celsius. In order for the glaze to be included as part of the stoneware or porcelain, the kiln must reach a temperature where, among other things, the quartz in the clay fuses with the glaze’s quartz. At the last 100 to 150 degrees, the glaze melts out and the crystal-forming substances contained in the glaze form nuclides which are the central point of the crystal formation. If the heat is then lowered to 1080 degrees and the kiln is allowed to stand at that temperature, crystal wires will grow out of the nuclide core. At 1080 degrees, round crystal flowers are usually formed. At 1130 degrees rod crystals are formed. If I raise and lower the temperature five times, I get five rings around a crystal. If I raise the temperature from 1080 degrees to 1140 degrees, these rings are formed inside the crystal,” explains Isaksson.
Isak Isaksson feels that different types of expression are suitable for different types of forms: “Balance is important. On a more bombastic shape a calmer glaze feels best and vice versa. But sometimes it’s fun to go all in and not care so much about right and wrong!”