Ash glazes have been great novel fodder!

Actually, legend has it that the first copper red glaze happened by accident as a pig ended up in a chinese potter's kiln before (and therefore, during) a firing of a copper blue/green chun glaze.

The potter never discovered the reason for the beautiful red glaze produced by the additional reduction of the glaze in the early part of the firing. There was nothing left of the pig by the end of the firing.

But the emperor was so taken with this beautiful glaze that he ordered the potter to make more.

Try as he might, the potter could not duplicate the results of the firing. Always green, never red.

Finally desperate and inconsolable at his failure, he threw himself into the burning kiln.

....the emperor got his red glazed pottery. Emperors always get what they want. Potters always work too hard and die.