Bonnie Staffel on sun 22 jul 01
Dear Lela,
I have used the mothball method of achieving copper reduction in my electric
kiln for many years. This is done on cooling when the pyrometer reads
around 1500 degrees. However, mothballs are very explosive when they enter
the hot kiln through the peephole. What I found happening was that the
glaze surface suffered from this sudden flash of fire. This was done with
earthenware clay objects. However, when I bisque fired my porcelain pieces
to maturity and then applied my Cone 04 glaze, I got beautiful reds and
sometimes lusters to die for. Getting the glaze on mature porcelain is
rather involved but it can be worked out. I would heat the piece, dip it in
the glaze, paint the copper carbonate, then using a spray gun, applied more
glaze on top to make sure there was enough thickness. This takes a lot of
experimentation.
However, this is a very noxious method and you need to leave the studio
during the smoking process. I would add the mothballs whenever the smoke
subsided, until the temperature was reduced to 1000 degrees. When in
Denmark, they had a kiln available with tunnels under the floor of the
electric kiln with tiny holes going up into the chamber and an exit hole in
the top. Instead of moth balls, I used candles in the tunnels. No
flashing, just a nice steady smoking and I believe I used about four tapers
to do the whole reduction. I also covered the hole in the top. When I
opened the kiln, every piece was perfect. The class tried many decorating
methods, not just a solid red. A wash of cobalt also adds a nice color
break from the red.
I think that if you could wrap pieces of old candles in aluminum foil and
use instead of moth balls, there might not be the flash. I also considered
creating a buffer chamber with IFB to keep the combustibles from flashing or
from causing problems with the glaze.
Above all you must leave the room during the smoking process even with an
exhaust system. Carbon monoxide and other toxic gases are involved and it
does not need to be in your lungs. Just step outside your studio so you can
watch the smoke. When it stops, go in with another candle, insert and then
leave again.
Good luck. Bonnie Staffel of Charlevoix, MI.
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