Black Raku

[Fredrin]

Every once in a while, a student will come into my workshop and point at a priceless 16th century masterpiece by Chojiro or another grand master of the Raku line and say "I want that one"...

I usually roll my eyes, say "you know not what you ask" and direct them to a commercial copper matte, which they're mostly pretty happy with.

But maybe I'm being defeatist!

I've done a fair bit of haphazard research about Black Raku over the years and it has thrown up a lot of contradictory info. One particularly interesting nugget is that the black glaze was made from special manganese-rich stones found in the river Kamo. Kamogawa stone is now heavily depleted so next to impossible to obtain apparently.

In terms of the firing, many sources say it would have been in a charcoal-fired kiln to temps as low as 500-650°C, meaning it most likely contained raw lead. It would have been taken from the kiln at top temperature, with no post-reduction as is common in modern Raku and apparently dunting was actually desired as the distinctive sound which dunted ware gives when struck was valued in the zen experience of the tea ceremony.

Has anyone done much exploration into achieving the kind of surface finish pictured above? Does anyone perhaps have a recipe they'd be willing to share - ideally maturing at more conventional Raku temperatures like 900°C?

My last attempt using this recipe from Glazy resulted in more of the glaze ending up on the kiln shelf than the bowl due to 'decrepitation' of the colemanite - a brilliant euphemism for violent decomposition, I later discovered.

https://glazy.org/recipes/11950

Any pointers that don't require the building of a charcoal-fired kiln are welcome, though that would also be a fun project, I guess...