Glazing has an aesthetic side and a mechanical, physical side. I want to draw attention to the actual act of glaze application and its implications. The way you apply the glaze determines how it will look. You could ruin your pot, or make it spectacular. Good glaze application techniques are critical to your success.
The first thing you need to understand is that the glazes, in their liquid state in the buckets, are a mixture of minerals and water. However, when they are fired, the minerals in the glaze will melt and form a glassy coating that fuses to the clay. Secondly, the porcelain clay, at maximum temperature, is so hot that the clay becomes as soft as it was on the wheel. So pots can actually slump and collapse if not made properly.
Glaze melting and fusing takes place as the kiln approaches the maximum temperature. The melting glaze (glass) behaves like honey. The hotter it gets, the more fluid it becomes… just like honey does when you heat it in a microwave. Sticky, thick honey can become as thin as water when heated. The word “viscosity” refers to a liquid’s fluidity. Water has low viscosity and is fluid at room temperature. Honey has a high viscosity and is thick at room temperature. Glaze and glass, like honey and tar, when heated become less viscous and more fluid.
In addition to becoming more fluid, glazes also go through a boiling phase, which essentially stirs up the ingredients, causing mottling and mixing of colors. Chun and Oil Spot show these mottling effects.
Finally, you need to understand the cooling process. When the pots cool, they get hard and rigid again, as do the glazes. At certain points in the cooling, crystals may form in some glazes. Plum and Tomato Red are examples of glazes that have crystals in them. This is also where glaze fit becomes an issue, causing some glazes to crackle.
As mentioned before, good glaze application techniques are critical to your success. The glaze application can cause the glaze to run off the pot in the firing. Here’s how:
- The thicker the coat of glaze, the more likely it is to run.
- Glaze overlaps are always more fluid. This is due to chemical reactions called eutectics, and also because two layers of glaze are thicker than one.
- Some glazes are inherently more fluid than others. Copper Red and Oil Spot always become runny in the firing. Plum is an example of a not very fluid glaze.
The above three things need to be taken into account when you apply glaze. You will be shown in class how to apply glaze. Not all glazes are applied the same. The color of overlaps is not what you would expect with colored paint. Some glazes are easy to use. Some are difficult. If you understand the above information the instructions you receive in class will make sense to you. If not, it will seem like a jumble of arbitrary rules and be quickly forgotten. So think about the above. Ask questions in class or do some research, and be prepared to LEARN PROPER GLAZE TECHNIQUES in class.
In conclusion, if you don’t glaze properly your pots will be ugly and possibly damage my kiln as well. Fortunately, Fireborn glazes are incredibly beautiful, so if you learn proper techniques, you can make even a humble pot into a thing of beauty.