My Ceramic Spectrum

[offcntr]

The first year I did the Best of the Northwest Holiday Sale, I happened to be three booths away from another ceramic painter, a fellow with paintings on porcelain tile. Friday was sort of slow, so I was playing with my demonstration brush and magic paper (sumi-e practice paper that turns black with water, then erases itself as it dries), and invited him to have a turn.

He turned me down with a sneer, saying he never used "stick-and-hair" brushes, but imported his at a premium from China. He added that he couldn't paint without at least six distinct and distinguishable shades of red, and I don't know what all else because I was still steaming from "stick-and-hair."

It gave me great and only slightly guilty pleasure to outsell him all weekend.

But I like a limited palette. I'm not making fine art for the ages, I'm painting pots. I don't want to have to pause and decide between six shades of red when painting a flamingo mug. I'm good with one.

Here's my standard spectrum, left to right as I set up my station:

Black. A lot of people make black from scratch by mixing a bunch of different metal oxides. I prefer it simpler. Chrome-free black Mason stain, mixed 50:50 with Gerstley Borate. About a teaspoon of each with enough water to suspend will fill a 35 mm film can. I want it about the consistency of ink for line drawing. Chrome-free because chrome is refractory (resists melting) and a chrome-bearing black stain will bubble and blister. (Edited 2023: Mason no longer makes a chrome-free black. The lowest-chrome black they make is 6600. I have to mix it 1:2 with Gerstley to prevent blistering.)

Blue. Straight cobalt carbonate. I have full strength in the bottle, and dilute with water in the cap for shading, shadows. Cobalt has a lot of tinting strength. You can dilute it three or four times and still have a shade of blue. (I also do the dilution trick with the black to give me grey shades for everything from shadows to crows.) The one drawback to painting with cobalt is that it changes color in the firing. The raw mineral is lavender colored, the finished pot, true true blue.

Yellow. Rutile is a mineral containing roughly equal parts of iron and titanium oxides. I use it straight in water to get a gold-yellow color not unlike the ochre horses in cave paintings.

Red. I used to use copper carbonate for reds, but it's so dependent on kiln reduction. I'd wind up with roosters with liver-colored combs, or even apple green, as often as red. But all the other choices for red in ceramics only worked at low temperatures. In a stoneware kiln, they'd burn out and go up the chimney. Then a company called Degussa invented zirconium encapsulated ceramic stains, reds and yellows and oranges that were stable at cone 10. Now made by Cerdec, they're spendy as all heck, but I use them by the teaspoonful, mixed 50:50 with Gerstely like the black stain, and do a lot more patterns with red these days.

Orange. I wet-mix equal amounts of rutile and red stain. Much better that the Degussa orange, which is kind of anemic.

Brown. I'm still using the Cardew iron overglaze recipe I learned at Tuscarora. By weight, 80% red iron oxide, 20% Red Art clay.

Green. Green is traditionally chrome oxide, which is bright grass green in unfired state as well. Pure chrome interacts oddly with my base glaze (Third-Best Possible White. I've made some changes over the years), coming up a muddy peach color. To compensate, I use a mix of chrome oxide and cobalt carbonate, but since chrome is refractory, I've taken to mixing in Gerstley Borate as well. By volume, a quarter chrome oxide, a quarter cobalt carbonate and half Gerstley.