Experiments With Copper Inlay

Recently I’ve been experimenting with clays and techniques I haven’t tried before. There has been much discussion elsewhere about the new clays, so I’ll let you know about the results of my inlay experiments.

My first trials were on a few pieces from the “to the refiner” pile; a pair of button earrings and a pair of cufflinks, all Art Clay Silver. In the first earring, I inlaid pure copper and torch fired the piece according to ACW’s instructions. While the clay sintered properly and looks okay, it did have the typical open-air firing oxidation that chipped off, not a look I like. The second earring was inlaid the same way, but fired in charcoal using Hadar Jacobson’s temperature for the second phase of her white bronze . This piece fired successfully, the copper held in the impressions well without chipping.

Next I stamped out two pieces of Art Clay silver to inlay unfired.  The first was inlaid with pure copper and the second with a 75/25 copper/silver alloy made from ACS and ACC. Both of these were fired open air on a bed of charcoal full ramp to 1100 for 10 minutes, then covered with charcoal and full ramp to 1360 for an hour and a half. The pure copper inlay chipped in some areas, while the alloy had no chipping and a nice surface. However, the contrast between the silver and copper/silver alloy was not as strong as I would have liked, although it looked better with an application of Baldwin’s patina. Since the pure copper did not chip from the prefired button earring, I wonder if I should have fired longer or hotter or if my inlaid was not done well and will try this again.

Because the alloy inlay fired better, I decided to try inlay in sterling clay. I made up six test pieces with PMC Sterling; three for inlay in a fired piece and three for inlay in an unfired piece. While firing the 3 pieces to be inlaid in a fired piece, I also fired the cufflinks with the 75/25 copper/silver alloy.

The cufflinks displayed an eutectic reaction between the copper/silver alloy and the fine silver button/sterling shank, forming an unknown alloy due to the high firing temperature, and were now a dull grey, not the copper alloy they had originally been inlaid with. Not being a metallurgist, I might have some of this wrong, but, as I understand it, when two metals are mixed, as in an alloy, it lowers their melting point and an eutectic reaction occurs. Enamelists can see this when using silver cloisonne wire on copper. If the silver sinks through the enamel basecoat and touches the copper, it will form an unknown copper/silver alloy. This was the only time I had a eutectic reaction, and the only time I fired the copper inlay at this high temperature.

For the sterling inlay, I used a two phase firing. All the test inlays in sterling were successful. I got sloppy on one copper/silver batch (late in the evening when I mixed it) that shows some unmixed silver in the copper, but it  sintered properly.  The first fired/unfired inlay pair were pure copper inlay, the second set were 90/10 copper/silver alloy and the third set were 80/20 copper/silver alloy. The unfired sterling inlays have a nice smooth surface, while the prefired sterling with inlay were textured. Both would be effective for different looks.

The unfired sterling bases successfully sintered at the lower temperature. I could not bend the pieces by hand and they were only a tiny bit larger than the sterling fired at the manufacturer’s recommended temperature. I did not try hammering them, but this is something I will try.

Lastly, I decided to inlay some silver into a prefired copper piece and found a reject copper piece and just “smooshed” some silver in it. This was sintered in a single phase firing in carbon to 1360 degrees. Again, a successful firing, in that the silver sintered, but there was some cracking due to shrinkage, which could be filled but wouldn’t be…..as I now wish I’d picked a nicer piece, as this is rather ugly and a waste of silver.

In most of the experiments, I liked the pure copper look better, but I think all alloys used in a single piece could make a nice shaded piece and this is something I want to try. I can just see a tabby cat sketch done with copper inlay on silver or could I do a sgraffito technique on a layer of copper over silver or vice versa?  Oh, the possibilities!!  I still have experimenting to do – more alloy combinations, different hold times and temperatures, and more trials in pure silver, “homemade” sterling and using Hadar’s copper rather than the ACC clay and will let you know how it all goes.  Please try this yourself, I’d love to see some pictures of your work.

I would like to thank Mary Ellen D’Agostino and Hadar Jacobson for generously publishing information on their experimentation with alloys and firing as without this, I most likely would not have been successful with my inlays if not for their freely given information.


About Mikki

I am a metal clay artist, living in Londonderry, New Hampshire. I teach from my home studio, at Metalwerx in Waltham, Mass and various other venues throughout New England. My work can be found at the shops of the League of New Hampshire Craftsmen and local galleries. You can see my examples of work at www.everlastingtreasures.org

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