F.Forsythe on sun 19 may 96
I have had a lot of trouble with boiling glazes at cone 6 electric
oxidation firings. However last night I had a perfecto firing. I posted
something about pin holing a couple of days ago but for some reason it
didn't show up.
I used to fire at about 100-150f /hour until ~2190f. Then I would hold
the kiln until Mr. cone 6 bent over. Then I would shut off the kiln.
This got me lots of bubbles.
I revised my firing schedule by soaking down (dropping the kiln down the
first 100f degrees slowly. This helped - a bit...
Finally I took the kiln up to 2160 (faster than before) but held the
sucker there until Mr. cone bent over. This took about 2- 3 hours! BUT
there were no pin holes, bubbles, acme etc. Well worth the wait!
Now I have to revise my recipes because many glazes look a bit
different.
This leads me to believe that glazes could be dealt with in terms of
boiling points and not just gassing problems. In other words some glazes
have more room between melting temp and boiling temp, while other glazes
have almost no room between the melt and the boil points. I solved my
problems (so far) by forcing the glazes to melt a little below the std
melting point and therefore below the boiling point.
Yes, yes I know there must be all kinds of people out there shaking
their heads and saying Rookie!
Well it took me a long time to figure it out. And I suspect I am not
alone. I hope this makes sense to someone. My boiling problem was not
carbon matter in the clay body or troublesome glaze materials. It seems
to be just like the boiling point in water. -you reach a critical temp
and bang you got boiling.
Any comments please.
Fraser
forsythe@sentex.net
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