Uneven Bowl Slumping -- the Cure
This is part five of a
multi-part tip on preventing uneven bowl slumping. Click here to go to part one.
So what do you do if despite all your efforts your bowl emerges
lopsided from the kiln? Is it a total loss?
No, not at all. Even the most lopsided and out of round
slump can be salvaged. It just requires a bit of time and some
re-firing. Unless you have hundreds of dollars of cold working
equipment and dozens of hours to devote to the project, the best way
to fix a lopsided bowl is to fuse it flat and slump again.
Start by placing the bowl on the kiln shelf, right side up.
You want to fire slowly, slower even than when you fired the glass
to slump the bowl. For two layer bowls, increase the
temperature as slowly as 300 degrees F (167C) per hour. Go
even slower for thicker items.
Once the temperature reaches 1100F/600C, soak for at least 10
minutes. Then take about an hour to reach 1200F/650C. If
the bowl hasn't slumped flat yet, continue increasing the
temperature slowly to 1275F/690C, then maintain that temperature.
You want to continue firing until the bowl flattens totally, taking
care not to go above 1300F/700C.
Watch the bowl until it flattens, making sure that it smoothes
out completely. Then anneal as normal.
When the blank (no longer a bowl) is cool, check to see that it
is still round. It may have distorted slightly during the
firing, so some edgework may be necessary. After you're
satisfied that the piece is ready for slumping, you can fire again
in your mold. Go slower this time than on your first slump
attempt; that will guarantee the best possible finished bowl.
Copyright 2006 Brad Walker.
All rights reserved.