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I have a great tip for you, to make bisque firing simpler and more
successful. I'm not at all interested in the technical aspect of firing and
this has saved me from having to pore over books and do a lot of
experimentation. Excuse the lack of technically accurate firing terminology;
I'm no pro on this.
I was told to hold a mirror upside down over the "peephole" and check from
time to time to see if steam is still escaping from the clay. The moisture
will show up as fog on the mirror. When it no longer gets fogged up, you
know it's safe to plug up the holes and let it finish firing.
I step up the heat gradually, an hour on low, then two hours on medium, and
then I step it up to high. All this time the plugs are left open. After an
hour or so, while it's firing on high, I keep checking with the mirror.
(Don't store the mirror near the hot kiln; it won't work unless it's cool.)
When it's fired on high for a while (takes a few hours for me) and is
fog-free, I put the plugs in the hole and leave it on another couple of
hours. I turn it off and let it cool overnight.
Someone with more firing expertise may be able to suggest improvements to
this firing schedule. Perhaps it's not necessary to leave them in this long?
This has worked great for me. I almost never have broken pieces, and my
students are not all that careful about wedging their clay. I mention air
pockets to them, I feel it's my duty, but I don't obsess over them like I
used to. I was told that if you follow this procedure, air pockets won't
cause any breakage. Seems to be true, hope it helps you.
Karla in Arkansas