Firing temperatures in Japanese pottery

[Tamas]

Hello everyone,

 

 I have been watching some Japanese videos about making kohiki ware lately (like this one: https://www.youtube.com/watch?edufilter=NULL&v=bdwDsUNL0f8) and noticed that they bisque fire to 700  degrees centigrade (which is like cone  018?) and glaze fire to 1230 degrees (cone 6-7) in reduction. Is their clay that different, or is there some other consideration behind this technique? Can organic matter fully burn out with that bisque technique?

 

Thank you

 

Tamas

[Min]

Organic carbon burns out  from approx 150–320°C. Inorganic carbon from clays  burns out from 700–900°C. Sulfur will burn out from 700 - 1150C .  So a bisque of 700C is just starting to burn out the inorganic carbons. The clay could be sintered but it's going to be a very soft bisque. I don't know enough about kohiki ware to know if a 700C bisque is the normal practice. Maybe it's a compromise between raw glazing and bisque firing to higher temps.

[Tamas]

Thank you, Min - but what is the payoff? The cost saving can't be that enormous? Will the glaze behave dramatically differently during the glaze firing?

[Min]

I think what’s happening with the really low bisque is that it would actually encourage glaze pinholes which is what I believe helps form the iron halos in the white / porcelain slip that covers the high iron clay.  I could see raw glazing working for this effect also.

[Tamas]

Interesting, and makes sense! Thank you.