It contains no iron but does have a little cobalt. The ash is about 50%, with 20% kaolin and 25% feldspar and a little rutile. However your ash will be different so you will have to do your own development program.
Wood Ash Glaze
Common washed wood ash has a chemistry akin to a ceramic glaze, so it can comprise significant percentages in a recipe. Plus it can produce unique visual effects.
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