Saturday, 17 September 2011

Experimenting with terra sigillata once more

I thought I'd show a couple of pots from yesterday's firing. I wanted to find out whether terra sigillata would stay put when painted onto bisque-fired pieces, so I decided to try it out on three lidded boxes. I mixed a couple of grams of yellow iron oxide into some liquid, white terra sig. (no accurate measurements taken this time), and as you can see, it's come out light yellow in colour. Ideally, I would like it to have been more of a rusty orange, but I still like this result.

I'll have to wait a while to see if the coating of terra sig. will stay put as one of the boxes has already peeled, I think where the clay was way too smooth. I remember I had smoothed these pieces, almost to a shine, with my fingers and terra sig doesn't really like sticking to burnished surfaces. When I've used it in the past, I've noticed that a pot can look perfectly fine for a day or two, and then, maybe once the clay has contracted and expanded with temperature changes, it suddenly starts flaking. So, brushing onto bisqued ware hasn't eradicated the problem altogether, but there is a definite improvement..I just need to make sure I leave the clay surface fairly rough from now on.

These terra sig. pieces were fired to 1100 degrees C in a sealed saggar with a little charcoal, and I bisque fired a few other carved pots at the same time. I realise this is pretty high for a bisque firing but I want them take up less glaze, and this is one way to achieve that. The good news is that my carved pots came out cracking or splitting this time, thank goodness!

Interesting too, that the the box in the first photo is a deeper yellow, as the terra sig. was applied over a clay body containing more iron. The second piece was made from a lighter coloured clay body..a 50/50 mix of original raku and a pale stoneware clay.

Carved, lidded box. Approx 3 inches long

Carved, lidded box. Approx. 5 inches long

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