|Monthly Tech-Tip |
Top to bottom: Cone 10 reduction, cone 10, 9, 8, 7 oxidation. Fire-Red is a mix of St. Rose Red fireclay, M2 Montana medium fire red clay with some dark burning A1 ball clay. This blend is less refractory than pure St. Rose Red and much more plastic, thus more suitable as a body addition. The color shift between cone 9 and 10 oxidation occurs because of the fluxing action of M2.
We get this clay from St. Rose, Manitoba. Four tandem loads arrived this week. Just seeing the pile inspires me to make more pieces! It is a red fireclay and it is highly unusual. St. Rose Red has issues. They at first seem to be problems, but in combination they give it magic powers! It fires with very heavy iron speckling. The iron pigmentation is so high that it burns almost black at cone 10R. It has low plasticity. It shivers glazes: The vase on this picture lasted an hour after kiln exit, it spontaneously fractured because of the outward pressure from the under-compression glaze on the inside. But, by combining St. Rose Red with our more vitreous clays, which are highly plastic, we can make H440 and H443. A mix of only 45 St. Rose with 40 Ball clay and 15 feldspar produces a rustic metallic surface (like the cup shown). Such a body cannot be made from a low fire red clay (like RedArt), it would just warp and collapse in the kiln. It is the refractory character, heavy pigmentation, iron speckling and low plasticity of St. Rose that make metallic ware possible.
Saint Rose Red