Monday, May 16, 2011

Dealing with Distortion

There's nothing more frustrating that working hours to refine and prefect a piece of metal clay greenware only to have it emerge from the kiln wonky and distorted. This is a problem particularly with our higher shrinkage metal clays. I'm always frightened of opening the kiln box, because I've been burned one too many times... actually if I were literally burned, just a little, that would be preferred to the dismay of lost work.

After a few years of squint-eyed brain cramps, I've begun to unravel the distortion mystery. There are two major factors that cause our elaborate base metal clay pieces to fail in that final stage: Heat and Obstruction.
Heat is pretty easy to deal with, it's really a matter of even heat saturation. The entire piece needs to be heated up to the same overall temperature at the same rate. Lowering the ramp up time to 1000F-1100F (in the case of COPPRclay) per hour allows the greenware to absorb the heat more evenly. Where we position the piece inside the firiring vessel also dictates heat exposure. Make sure the largest surface area is facing the heating elements, so flats need to be standing vertical inside the firing chamber (see illustration below.)

The second major factor is obstruction. We pack our little firing vessels full of carbon, then nestle our delicates inside never suspecting the culprit of our future woes is staring right at us.... the dreaded carbon particle. When metal is heated to those extreme temperatures it softens and can't push those unassuming particles out of the way. So what to do? Hattie Sanderson's Steel Wire Mesh Cloth! Mouthful, I know, but it's a fantastic solution. You can fold it to create a little dome, I just cut it into squares then dog ear the corners, and use it as a lid over any openings in my metal clay that I want to keep clear of carbon particles (as demonstrated by my fantastic kindergarten style rendering below.)

When I fire a tube shape I will actually stand the piece up on a flat bit of mesh, fill the firing vessel to the outside rim  of the piece (leaving the inside of the greenware clear of carbon,) put mesh on top  of the piece (I dome the mesh a little to leave air space above  the greenware) then fill the remainder of the firing vessel with carbon.

I thought I could outsmart distortion all together by creating wire mesh cages, that protected the entire piece from carbon particles, but it turns out gravity can be just as destructive... I ended up with very depressed looking slumped forms... go figure. So you still need some carbon to prop up the outside of the form, while keeping it out of those spaces that can ruin your design. Hope this helps!

Oh, and rememeber, I'm still giving away two copper clay necklaces! Check my previous post for full details: Send a Friend Giveaway

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