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Blue on Black
This glaze has only worked properly 4 times from 150 attempts,
and only on small pots like this (about 31/2" - 4" high), never
on a large pot.. Too often the black has brown patches showing, and they
never improve by re-firing.
Vase (colourant, copper and iron
oxides)
The shape of the pots sometimes helps with the placement
of the crystals. Crystal glazes are very fluid, and on this vase, the
shape slowed the flow of the glaze, to leave some nice crystals on the
shoulders.
Sometimes, if the glaze contains copper, and has nice
crystals, I refire the pots in a simple little gas kiln, to about 750°
C. This will not affect the crystals. I then throw in some old cooking
oil, which creates a smokey atmosphere, and the reduction of oxygen in
the kiln will change the copper green to variable red colours.
The Colourant for the piece below left is 1 and 2 cent
coins,
the piece below right uses copper wire and steel wool as colour variants
the piece below right uses copper wire and steel wool as colour variants
What a difference a clay makes.
This is the same glaze on each pot, the difference is caused by the different clays used to make the pots. As you can see, they were fired very close together in the same kiln firing!
Copper wire laid on top of glaze.
The glaze on the next three pots contains zinc, so the copper spread
as it melted, giving a dense crystalline effect. They were fired to about
1180° C in an electric kiln.
The glazes on the next two pots (below left and right)
are stoneware glazes that contain no zinc, so the copper did not spread,
and one finished up looking like a squashed rat, instead of a tree.
They were fired to about 1260° C in an electric kiln.
They were fired to about 1260° C in an electric kiln.
Steel wool
Steel wool included in the glaze, same glaze on both. On the left, oxidised in an electric kiln to about 1260° C, on the right reduced in a gas kiln at about 1260° C
Steel wool included in the glaze, same glaze on both. On the left, oxidised in an electric kiln to about 1260° C, on the right reduced in a gas kiln at about 1260° C
