The silver and copper tube bead project was a raging success!! Almost every one came out beautifully. One student didn't seal her seam well enough and it split open during firing, but I still like it. They'll wire brush and patina tonight and I'm really excited to see how they finish up.
the black residue is copper oxidation. most popped off when I quenched in water and the rest can be removed with a wire brush. if there is still some remaining we'll make a pickle with hot water and 3 tbs Alum from the spice aisle of the grocery store.
Here's what we did. I used my Tubing Cutter Jig from Rio (page 139 in the Tools catalog) to saw thin copper tubing from the hardware store into 1.25" lengths. I drilled holes at the top of half of them so they could be strung vertically and the rest I left in tact.
seam split open during firing
The students sanded the tubes to clean and prepare the surface for the clay. A bit of "tooth" always helps. Then we dampened the tubes just to help the fresh clay stick and used PMC+. I fired at 1470 for 40 minutes using a slow ramp and voila! I think Vicki Cook likes to fire lower but I only had Plus on hand and the lowest temp that it can be fired is 1470. You could also use PMC3 and fire at 1200 for 45 minutes.
metal clay doesn't fuse to the copper, but shrinks to make a mechanical connection
Make sure you use really fresh clay so the edges don't crack, wrap the clay so that it touches the copper, but loosely enough to accommodate the shrinkage, don't stretch the clay. Remember to sand all edges including inside of holes. I like to use a toothpick or a dampened paintbrush. If you try your hand at this, both Vicki and I would love to see your results.
Yesterday a student who I haven't seen in at least a year brought over some pieces for firing and I had quite the surprise when I opened the kiln. These were perfectly flat when they went in but look at them now. This is what aluminum contamination looks like!
She left them to dry on aluminum foil. Baaad. Aluminum and petroleum don't play nicely with silver metal clay. Steel is suspect too. I once formed a pair of earrings on the punches from my dapping set and some small black spots had formed by the time I removed them. Luckily they fired up just fine. So let this be a lesson. Some urban myths aren't myths at all!