|Monthly Tech-Tip |
Tenmoku reduction fired glazes can be so beautiful yet few people use them. One reason is the melt fluidity - runs stick pieces to the kiln shelf. While the melt fluidity is the key to the appearance it is also the curse. These glazes also pool on inside bottoms producing glaze compression issues. And they stretch thin over rims roughening them with any grit from the body or glaze materials. The running onto the shelf issue at least does have a simple solution: The GR10-A base as a catcher glaze on the outside bottoms and a liner on the inside (and even optionally wrapping over the rim). 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 thickly and it’s no problem, 5-10 mm of catcher glaze is all it takes to stop the running.
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.
A catch glaze of the lower section of a piece of ceramic or pottery is often needed to arrest the flow of reactive runny glazes (so they do not run down on to the kiln shelf).
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.
Glaze is excessively runny on firing