|Monthly Tech-Tip |
Tenmoku reduction fired glazes can be so beautiful yet few people use them. Why? The melt fluidity is the key to their appearance but also the curse. They pool on inside bottoms producing glaze compression issues. Runs stick pieces to the kiln shelf. They stretch thin over rims roughening them with any grit from the body or glaze materials. All three issues have a simple solution: The GR10-A base as a liner glaze that wraps over the rim and as a “catcher glaze” at the bottoms. I use a dipping glaze version of it for the insides and a brushing glaze version for the bases (and up the side walls about 1cm). The tenmokus GR10-K1 (left) and GA10-B (right) can be applied thicker than I would otherwise dare and it’s no problem, that 5mm of catcher glaze is all it takes to stop the running. Another benefit: Now it is also possible to use these glazes on stonewares, not just porcelains.
This iron red cone 6 glaze, G3948A, is applied thickly and runs during firing. With no countermeasures, it ends up on the kiln shelf (like the one on the left). Since this glaze breaks-to-black where thin on the edges of contours, glazing the base black seems like a natural match. The base of this was first dipped in G3914A black, up to about 1 cm (1/2 in). I then waxed over all of the black up to within 1-2mm of its edge. Then I applied the iron red by dipping in the normal way for liner glazing mugs. For this thickness of the brown the black melt is able to catch and stop it within 5mm or less.
Many ceramic glaze benefits and issues are closely related to the thickness with which the glaze is applied. Many glazes are very sensitive to thickness, so control is needed.
Tenmoku is a kind of high temperature reduction firing ceramic glaze. Glossy, very dark brown or maroon, fluxed by iron oxide to have high melt fluidity.