Black slip-glaze

Lately, I've been experimenting with various types of black slip and engobe for firing in oxidation. I'm really looking for one which will work well under a semi-transparent stoneware glaze, so I can develop some Japanese-style painted decoration on my pieces. This recipe actually looks quite effective on it's own as a black slip-glaze, when fired to cone 8/9..one advantage being that it brushes on to stoneware very easily, either at the leatherhard stage or after bisque firing. So far, it appears very reliable and doesn't peel off or crack. It creates a fairly matt surface, but has a very slight sheen to it as well. The small bowl pictured below was given two coats on the outside.

Black slip-glaze recipe:

Keuper red clay 100 (dry weight)

plus

4% manganese dioxide

4% iron oxide

2% cobalt oxide

Bowl with black slip glaze and matt ochre ash glaze inside