This is the third post focused on focused on my new glazes and work. Read part 1 and part 2, too.

When I try a published glaze I experiment on different clay bodies, and in different areas of the kiln. I then refine the recipe over the course of many firings until satisfied. The same, of course, goes for my own glaze creations, though mine are more experimental and may never, ever, turn out. I’ll write more about experimentation in a later post… I’m covering my glazing process for now.

I spray glazes over each other to varying degrees and thicknesses to obtain more color variation. Sometimes this is beautiful- sometimes hideous. Clay body, firing temperature, glaze thickness, reduction schedule (the temperature at onset of reduction, strength and length of reduction), and local material variations all affect glaze color.

Glaze thickness has a huge effect on color. Too thin and the glaze doesn’t develop good color, too thick and it can run or be a poor color. The same glaze needs to be thin on porcelain, slightly thicker on white stoneware, and thicker still on brown stoneware to develop the desired color. Some glazes are beautiful on porcelain, and terrible on brown stoneware.

Clay shrinks when fired. Bad glaze “fit” (making sure the glaze shrinks at the same rate and overall shrinkage as the clay) for a given clay body can cause crazing, crawling, or shivering. One must consider physics and thermodynamics in addition to coloration and texture.

Any glazes with rutile as a component are more prone to pinholing as a glaze defect. We have had entire kilns of our work go straight to the dumpster when these defects crop up. In the early 90s when I was trying to perfect a rutile blue we fired twice a week and went months without a success. Perhaps it’s contempt, but I’m no longer excited about rutile blue.

Now I fire a glaze firing every 2 or 3 weeks, and try to do some glaze tests in each. We are constantly learning and adding to our color palette. The somewhat frustrating and humbling part of being a potter is that once you give a piece up to the fire, anything can happen.

Right now I’m working on a custom set of dinnerware for a client with my sprayed glazing (see us unload it at 5 minutes, 57 seconds in to episode 3 of the Kiln Room). The dinner and lunch plates and large salad bowl are perfect. The pasta bowls and cereal bowls have pinholing on 60% of the pieces. Three bowls were fired on the same shelf – two of the three are pinholed. One is flawless. Why?

I really have no clue at the moment why this happened, but yesterday I threw ten more pasta bowls and 16 more cereal bowls to meet the order. You’d think after 40+ years I’d have this figured out, but it just doesn’t work that way.

We were at a 60th birthday party for a potter friend of ours a couple months ago with 6 potters with 35+ years experience each. We had this very discussion of how the kiln will throw you a curve every time you think you have the process down pat.

After all these years I still have only a tiny piece of the puzzle worked out.

This is the second post in a series focused on Michael’s striking new work. Read the first post here.

For the glossy blue and red glazes Michael starts with a clear glaze formula and adds colorants (metallic oxides). For dark blue, cobalt oxide; for light blue, a combination of rutile (rutile is titanium with iron impurities), cobalt carbonate, and red iron oxide. For red, copper carbonate, tin oxide, and a small amount of red iron oxide.

The matt blue is a low temperature copper blue glaze Michael modified for high fire. The yellow glaze uses yellow iron oxide as the colorant. Each glaze is in a different base. All glazes require extensive and continuous testing, and most glazes from books or articles haven’t worked as expected and need adjustment.

Michael designed and fabricated the kiln around his firing technique, which is tailored to our clay and glazes.