Firing away

Just unloaded my first electric ^9 kiln load in Canada.

A strange beast in Canada, where most electric is ^6 and most ^9-10 is atmospheric (usually gas). But I just returned from France, where ^6 is unheard of, and the world is divided into low fire or high fire. When I had done some ^10 reduction, but had no idea what to do at ^10 electric. And then it hit me – the one thing that you can’t do in reduction, and not in ^6 – Oil spot glazes. I was hooked.

Fast forward 6 months – I’m back in Canada, the realm of the gas kiln, sexy celadons and flamboyant flambe-s. But try to get a bright iron red in reduction. Or, of course, an oil spot.

The reason is simple. The way they work is through the thermal reduction of red iron oxide. That happens around 1220-1230C. So any firing cycle that reduces the iron earlier than that won’t produce the effect.

Now, the recipes for Oil Spot glazes that float around the internet and in books all specify that a long, hot, firing is necessary for the iron to bubble through the viscous glaze while letting the glaze heal. But I already knew that the French get oil spots to work all the time in a very pedestrian, general purpose firing cycle that reaches cone 10 or even just 9. Before leaving France, I did a line blend that suggested that the glaze I was using, or a variation on it, actually works at cone 8.

But I didn’t know what the French firing schedule would do in the kiln here. Or if the glaze, sourced from North American materials, would work the same. And in the back of my mind there was a suspicion that I don’t really have a handle on oil spots until I do some more glaze testing.

Well, I went ahead and rented the kiln at the Shadbolt centre, and went out on a limb – I went the big test tile way – big as in 12″ bowls and 8″ vases, not to mention about a dozen mugs and noodle bowls. OK – and a full biaxial blend based on Daniel de Monmollin’s 43rd diagram, that I put on bisque shards of which there is never a shortage.

And it worked. The spots were beautiful, the glaze was healed, and most of the 25 tiles in the blend produced spots, of varying sizes and surface qualities, and most of them healed. In addition, the new iron red based on DdM’s diagram#20 was even better than my French one, and the other glazes that I used to use produced their desired effect.  The pots are just what I wanted them to be –  elegant in their little black dresses/suits, but with the nice accessories of colour adding just an extra bit of interest, that welcome break with tradition/respectability that I like so much.

I wanted to take photos of them but then the clouds moved in and it started to rain. I’ll post pics as soon as there is some natural light of the drier variety.

Tomorrow? A guy can hope…






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