Convergent Series

learning, using & teaching metal clay, and other aspects of life

Trying Art Clay Copper (Post #2 of ?)

Posted by C Scheftic on 2011/03/08

In my last post, I mentioned digging into a second packet of Art Clay copper. That was unplanned! What I’d expected was to come back the next day, do a bit of fine-finishing on the pieces that would now be fully dry, and try firing that first group of pieces.

What happened, instead, was that when I came back, I found that the bails on the back of the two fish had cracked and broken apart! I made the bail-pieces early the first day and set those aside to dry. Then I made the rest of the pieces, ending with the fish. I did it in that order because the fish were formed in a little push-mold, and I figured I’d just keep making other pieces until what I had left was around the right amount to use for those: it’s just easier to push the last bit of clay into a mold to finish it all off than it is to roll it out into some reasonable shape.

(This image is an excerpt from yesterday’s snapshot, showing how they looked shortly before I left the studio.) I’d never before used those fish molds for metal clay. They are bigger (both longer and deeper), and thus require more clay, than what I typically make with silver. I had used a few others around that size in other copper and bronze experiments, and they’d turned out fine. I often push a dried half-washer of clay (any variety) into moist clay for either decorative or practical (e.g., hanging) purposes, and it’s always been a simple yet effective technique.

I didn’t think to take a photo of these in their broken-apart state, but here’s my theory on what happened. I have pushed semi-rings into clay as deep (even deeper) than this before, or into a shallow spot with as much clay surrounding it on all sides, but never both at the same time. As all the surrounding clay dried and started shrinking, could the force of that have caused the semi-ring bands to crack? In fact, on one of them, it did more than just crack open. There was further shrinking after the crack that caused the two pieces to offset a bit and slip past each other. (Made me think of certain kinds of earthquake…)

Since I’d used up my entire first pack of Art Clay Copper in making these, I had none left for making any sort of repair! I had bought a second pack (the smallest size available is 50 grams!) thinking I’d learn from any problems in my first round and then have another go at it later on. Since I had to open that one just to repair the fish bails, however, I decided to keep going. I don’t yet know how long this stuff will keep once it’s been opened. I do know it’s definitely for far less a time than one can leave an opened pack of silver clay, because the copper starts to oxidize from exposure to the air. So I used up the majority of pack #2, but this time I did set aside a small ball just in case I later found I needed to make yet more repairs!

I ended up with a few more pieces than I could comfortably fit onto a kiln shelf and fire all at once. (I might have just fit them all, but this stuff requires handling while it’s all quite hot, which I’ll discuss in another post, and I wanted to be sure to leave enough room to get a good grip on the shelf with my tongs….) So I selected out a few small pieces to fire the first time around. I include a snapshot of those.

The little “fan” and “ginkgo” shapes are from the first day’s batch; they’re face down since that’s the recommended firing position for one-sided pieces. (The ginkgo is a shape I have used with those semi-ring bails pushed into the step. Since I was trying to end day #1 with nothing left over, however, and I’d only made one of these, I didn’t do that this time. In retrospect, I wish I had, to compare with the fish. Oh well, I can test that another time.)

The two “pairs” towards the right are reversible; they are set to fire with their “flatter” side down. The theory is that the bottom side, in contact with the shelf, will develop less firescale. While I think of the side you see on these pairs as more likely to be the front, the other side is also nicely textured, though flatter. I figured it would maintain better contact with the shelf, so it faces down. I’ll just have to see what happens. Stay tuned for that report…

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