Martin Howard on mon 13 nov 00
One good rule seems to be always experiment on test tiles, whatever their
shape, before trying it on the larger pots.
In the last kiln load I didn't do that:-((
I have been trying to get a simple copper red heart on the bottom inside of
bowls, especially for wedding gifts etc.. All underglazes I tried went too
yellow or orange on me (cone 1-3).
So I tried Sic, raw. Perhaps readers remember that I had managed to get some
Sic 800 grade, instead of the 200 grade usually marketed here.
Well, instead of mix it into a base glaze with CuO at about .5 percent of
each, I impressed it loose on the bottom of bowls, just as powder (wearing a
mask of course), using dampened flexible heart shaped stamps.
It bubbled all over the place. Martian landscape. Some put on sides sloped
down to the base. The atmosphere must have really reduced for miles around.
All my other test tiles and many mugs were total write offs. All the more
for the hammer and the patio, after I have shown the mess to my students.
Perhaps someone who has really tested Copper glazes at earthenware cones
with SiC would correct me if .5 percent of each is way out.
But I will never put loose SiC into pots again after that one.
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ