Michael McDowell on fri 5 apr 96
It's a mystical experience that could almost be set to the tune of an old
Donovan song.
First there was no crazing
Then my glaze was crazing
Then it wasn't.
I first posted the clayart list some months back searching for help with finding
good glaze software. I had developed a glaze that could be used fairly thick on
my dark stoneware body at cone 11 that showed no trace of crazing. Sort of a
holy grail for a functional potter. But when I ran it through the Zakin glaze
software that I had downloaded from CeramicsWeb the program told me that it did
not conform to the parameters of a glaze! Eventually through Clayart I connected
with Ron Roy, Tom Buck and through them Tony Hansen & Insight software. Here was
software that at least didn't tell me that my glaze was not a glaze, even though
it did indicate an unusually low coefficient of expansion. Tom suggested that I
try freezing my pot & then quenching it in boiling water. If it past that test
without crazing or shivering he said it probably was OK. I liked the idea of
putting an apparently craze free glaze thru such a stress test. I have had the
experience of working with glazes that come out of the kiln & go off to market
apparently craze free, & then some months or years later i'll be drinking coffee
out of one of those pieces that I kept around & lo... What are all those little
dark veins all over the inside of my mug?
Well the piece stood up to the stress test, & I'm patting myself on the back
going Michael, you've got a nice thick craze free glaze here. So I make some
nice mugs with my white stoneware, use a rich celedon over incised decoration on
the outside & line them with my mystic craze free glaze. Well, for some reason I
thought to try the stress test on these, & guess what they crazed. Well I'm
going nuts. I'm working with help from Ron Roy at this point, and he's telling
me this glaze is already so low in expansion that these could easily be
compression cracks (i.e. verging on shivering). I'm imagining some unsuspecting
customer, or worse, myself, gulping down sharp little flakes of glaze with their
morning brew. But no, that's not what's going on, it's crazing. Then Ron comes
up with what I think is the unlikely Idea that my 10 hour firing cycle with a
good 45 minutes in between cones at the end is too fast! He says that he doesn't
think I'm giving my firing enough time to develop a good glaze body interface.
I'm not receiving this suggestion well, especially because I've got this really
tiny kiln I need to fire several times to get much work finished. But Ron is
firm with me & I agree to try following his suggestion to keep the kiln climbing
no faster than 150F/hr. If only to get him off my back about this. He's telling
me all the things that this slow firing will do for my glazes, improve the melt,
even out the kiln & I'm just hoping he's wrong 'cause piloting overnight &
firing from what turned out to be from 7AM til midnite just isn't something I'm
looking forward to doing a whole lot of. So what happens, I unload the kiln &
the pots look about the same, the little updraft kiln didn't fire any more even,
it's still a half cone
apart top to bottom (although now its the top that's hot instead of the bottom),
and I tell him all this in an e'mail that day while I'm letting a couple of mugs
cool off in the freezer. Next day I bring a big pot of water to a boil & drop
those mugs in one at a time. You guessed! NO CRAZING... Whoops! So for my
pennance Ron wants me to let you all know that slowing your firing down will
help your glaze fit & maybe some other things you could use too. OK, now I've
done it. Now I'm going right to work trying to figure out how to beat it. Those
are long hours for me, but you can't argue with the results.
Bottom line is, this Ron Roy dude knows some stuff, as do many others here on
Clayart & they are giving it away for the asking... Better listen!
Michael McDowell
Now if I could just shed my skin & find the butterfly within...
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