iandol on fri 22 feb 02
Dear James Bowen,=20
You say <firings turns iron bearing clays gray.>>=20
I have experienced this effect.
My understanding is that you will be reducing from a temperature below =
the incipient fusion point of your melting flux. This is what will =
change the colour of your Iron compounds in your clay. For Calcium to =
have an effect you would have to propose a chemistry. From memory, =
Barium Ferrites are red brown so I would imagine Calcium Ferrites would =
have a similar hue.
To get a bleaching effect the new chemical which forms must be either =
colourless or white, or it must be volatile and and sublime or =
There may however be alternative opinions.