Chemical reduction notes since the article was published.
It is crucial that a copper red glaze have barium and zink in it. The
zink is a strong flux that smooths out the glaze and probably because of
the extra melt, the red gets brighter. Barium has the same affect on the
glaze. To increase the zink or barium you may have to reduce other
fluxes.
The chemically reduced copper red glazes are more crucial to
thickness than a reduction copper red.
The firing cycle must be coordinated with the glaze so that melt will
capture the reduced copper and to be viscous enough to maintain the
reduced red in the re-oxidation of cooling. This was proven when test
tiles fired alone provided great reds, but then when a kiln load of pots
were fired, the reds went dark and grayish. I assumed that the fuller
kiln fired and cooled slower and messed up the reduction re-oxidation
process. It did and I increased ramp from 350 per hour to 400 degrees
per hour, 2/15/13 and the results were perfect.
Certainly every different formula is going to provide different color
and more specifically, different textures and patterns. Each could
require a different ramp speed for firing.
Different formulas will require different amounts of copper and
silicone carbide due to the beginning of melt and viscosity. 1/3% of
copper carbonate and silicone carbide gave the cleanest and brightest
reds.
Copper sulphate may produce darker reds, but may also cause grayish
black colors from too much reduction.
The larger the SiC particle size, the longer it's melt and chemical
combination with the copper.
