Thursday, 1 September 2011

A handful of test pieces

Please click on the image for a larger view!

The latest electric firing yielded some interesting test results! From left to right:

Test 1: This was a matt orange calcium  glaze applied over matt ash ochre glaze, fired in oxidation (only the top half shows the glaze overlaid). The result is a wonderfully smooth surface, almost like bone or tooth enamel. The colour is hard to describe..a kind of light greeny-yellowy-tan. The titanium and iron oxides have also run into the incised pattern, created deeper, mottled areas of pale orange-brown and tan. The colours are muted, but on the right piece it could work really well, I think.

Test 2: This is the matt ochre ash glaze again, but this time applied over a red slip. The red slip is Keuper red clay plus 5% RIO. The result is much,  much darker, and richer than the same glaze laid over iron-bearing stoneware clay. This was fired in reduction it would almost certainly come out completely black or very dark purple.

Test 3: Now this was interesting! Fired in reduction in a saggar,  this is the matt ochre glaze, but with the recipe tweaked somewhat.

I removed the iron ochre and replaced the koalin with Keuper red clay. The outcome couldn't be more different! The red clay has become as a much more active flux, and the result is more like a traditional ash glaze, with plenty of green glassy runs. I have read that calcium has a bleaching effect on iron and this seems to be happening here as it did on this piece below, where I overlaid a matt calcium tan glaze over the matt ochre ash glaze:

Carved vessel. Reduction firing.

Test 4: Another interesting trial piece! Some time ago I was trying to get a smooth terra sigillata finish by applying it to bone-dry greenware. I was having quite a few problems with it flaking off or peeling. It was a recipe by Anne Floche and really designed I think, for application to earthenware clays. I was using it on stoneware clays, and I suspect the shrinkage rate of the stoneware is lower than the terra sig when biscuit fired, hence the flaking off. The other day it occurred to me to try brushing the same recipe onto a pre-bisqued trial piece and then firing it to high stoneware. Miracle of miracles, it stayed on and with barely any cracking or peeling!! I need to test this further, perhaps with a slightly thicker can see that the terra sig is semi-opaque on this sample, but it looks highly promising!


Never give up..the best is yet to come!

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