Forty test tiles and one good blue
Commercial glazes are fine. They are also exactly the same as everyone else's commercial glazes, which is why I spent a wet August weekend mixing my own line blends from a basic stoneware recipe.
The base is a simple cone 6 satin. Across one axis I varied cobalt carbonate from a quarter of a percent to two percent; across the other, rutile from zero to six. Forty tiles, each with a dip line so I could see how the glaze behaves thick and thin.
Results
- Cobalt over one percent with no rutile is a flat, slightly aggressive blue. Not for me.
- Half a percent cobalt with four percent rutile breaks to a soft grey-brown on the edges and pools into a deep blue in the throwing lines. That one is the keeper.
- Anything with six percent rutile ran off the tile and onto the kiln shelf. Kiln wash earns its keep.
I have written the keeper on the inside of the studio door in pencil so I don't lose it in a notebook.