Terra fying
Apr. 19th, 2020 09:33 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
offcntrAnother project I'm catching up on: applying terra sigillata to some sculptural animal masks that have been sitting in my studio for over a year. I talk about the process in detail here; sadly, without pictures, as they're trapped in LiveJournal limbo. But here are some new pictures, and some rather nice looking masks.
A brief review: Terra sigillata is a highly refined, ultra fine clay slip, created by suspending an already fine-particle clay, like ball clay or earthenware, in water with a deflocculant, a chemical that slows down settling (I used soda ash). After a few days wait, the coarser particles have sunk to the bottom of the jar, so I carefully decanted the liquid from the top into another container and trashed the rest. This thin liquid has only the finest clay particles, microscopic plates that, when applied to a dry clay surface, can be buffed to a waxy sheen that maintains itself even after firing. Native American black pottery and classical Greek red-and-blackware both use this technique.
I have three colors of terra sig (well, technically, two-and-a-half): a white, made from commercial ball clay, a red from earthenware clay dug many years ago from the family farm in Wisconsin, and a black that's just white with black stain. Because the stain particles aren't as fine or flat as clay, it's not as shiny, but I like the contrast. If I had a ball mill, I could try grinding it down finer, but for spot color on one or two pieces every couple of years, it's not worth the trouble.
The first step was to blow all the dust off; did that outside, for the sake of my lungs. I shook up the sig's vigorously, as even with deflocculants, they'd settled over time. They'd also thickened up a bit, so I added water, more or less by eyeball. It wants to look like skim milk at the thickest. Then paint a small area with three coats, repeating as soon as liquid from the first coat had been absorbed. The masks were unfired at this point, so very absorbent. As soon as the third coat lost its wet sheen, but still looked darker than dry, buff lightly with an old, soft t-shirt or piece of dry-cleaning plastic. Continue until the entire piece is coated. As this is clay, not a glaze, I could theoretically cover the base as well, but as it's meant to hang on the wall, I didn't see much point.
For multicolored pieces, like the fox, I did the black first, then the white, and finished off with the red clay slip. I'll bisque fire these (once I have enough other pots to fill the kiln), then pit fire them in sawdust. The bear and raven will be buried in combustibles, in hopes of absorbing smoke and carbon to make them black. The fox will sit on top, and hopefully absorb just enough smoke for a little atmosphere.
A brief review: Terra sigillata is a highly refined, ultra fine clay slip, created by suspending an already fine-particle clay, like ball clay or earthenware, in water with a deflocculant, a chemical that slows down settling (I used soda ash). After a few days wait, the coarser particles have sunk to the bottom of the jar, so I carefully decanted the liquid from the top into another container and trashed the rest. This thin liquid has only the finest clay particles, microscopic plates that, when applied to a dry clay surface, can be buffed to a waxy sheen that maintains itself even after firing. Native American black pottery and classical Greek red-and-blackware both use this technique.
I have three colors of terra sig (well, technically, two-and-a-half): a white, made from commercial ball clay, a red from earthenware clay dug many years ago from the family farm in Wisconsin, and a black that's just white with black stain. Because the stain particles aren't as fine or flat as clay, it's not as shiny, but I like the contrast. If I had a ball mill, I could try grinding it down finer, but for spot color on one or two pieces every couple of years, it's not worth the trouble.
The first step was to blow all the dust off; did that outside, for the sake of my lungs. I shook up the sig's vigorously, as even with deflocculants, they'd settled over time. They'd also thickened up a bit, so I added water, more or less by eyeball. It wants to look like skim milk at the thickest. Then paint a small area with three coats, repeating as soon as liquid from the first coat had been absorbed. The masks were unfired at this point, so very absorbent. As soon as the third coat lost its wet sheen, but still looked darker than dry, buff lightly with an old, soft t-shirt or piece of dry-cleaning plastic. Continue until the entire piece is coated. As this is clay, not a glaze, I could theoretically cover the base as well, but as it's meant to hang on the wall, I didn't see much point.
For multicolored pieces, like the fox, I did the black first, then the white, and finished off with the red clay slip. I'll bisque fire these (once I have enough other pots to fill the kiln), then pit fire them in sawdust. The bear and raven will be buried in combustibles, in hopes of absorbing smoke and carbon to make them black. The fox will sit on top, and hopefully absorb just enough smoke for a little atmosphere.
no subject
Date: 2020-04-20 11:56 am (UTC)no subject
Date: 2020-04-20 03:31 pm (UTC)