I’m thrilled to be able to say it’s very strong when fired and lovely to work with when fresh. Like PMC Pro, it has a longer open working time than other versions of PMC. When dry, it’s generally similar to dry PMC3 or Plus except it's much easier to carve with gouges. It carves smoothly without chipping, like PMC Pro and like BronzClay.
Sterling PMC needs to be fired in 2 stages, a brief air fire and then a carbon firing. This is more complicated than the needs of fine silver PMC and at first it loomed large as a drawback for me. As I began to appreciate its strong points, however, the double firing became a lot more tolerable.
What follows is a brief story of my experience with the material to date. My plan for the winter is to explore more open work, more ring designs, hollow forms, and larger kiln loads. To be able to rely on metal clay for the kind of strength required by this type of work is thrilling to me. I look forward to developing ideas that I have been reluctant to do in PMC and also reluctant to fabricate in sterling metal.
Five Rings in Sterling PMC:
Please note: The times and temperatures I used in the firings described here were part of my testing process. The times and temperatures described in the PMC Sterling insert are our up-to-date recommendations for firing.
All of these pieces were fired at 1000F for 30 minutes then 1510F for 45 minutes, in well used coal carbon. All were fired with approx. 10mm of carbon on all sides (ie not much carbon).
The first (corset ring, 4 cards thick) was fired flat as a strip then keum-boo-ed on the inside surface with two layers of 24k foil (the gold adhered nicely, although a few tiny spots resisted the bonding). Then the strip was formed into a ring around a mandrel, laced with wire, patinated and polished.
This bee ring was fired face down and in spite of the band being thin, it did not warp or slump. The bee is quite thin, but strong and unmovable with my fingers.
The bee was more challenging to keum-boo than the corset ring, I think because the corset has no texture on the inside.
There was some staining on the surface of the bee that seemed to repel the gold. I tried cleaning it off but I couldn’t get the gold to adhere to some spots. This type of staining, after the carbon firing, has not happened again. The fact that the gold adheres as well as it does to the sterling without depletion gilding or any other preparation is still a mystery.
I made this ring to test strength in open work pieces and also attachments like the little balls, which I attached with slip. It did well on both counts. The ring is thin but strong and the balls are not coming off.
I fired this ring face down in the carbon with a piece of kiln paper under the cutouts and on top of the cutouts so the carbon granules would not jam into the cut out areas. This worked perfectly well although the ring itself is too thin to be practical. In spite of it being thin, it did not slump. I fired this ring with 4 other pieces; two hollow tubes and two flat pieces. All fired to strong metal.
(ready for firing)
This cylinder is the first hollow form I’ve made in sterling PMC. The caps on the top and bottom are donuts (rather than solid clay). I did this to conserve material. The cylinder did not distort in the firing; next time I will make it thinner walled and lighter weight.
I’m experimenting with firing more pieces in the carbon. The cylinder was fired with 4 other small pieces: 1000F in air for 30 minutes then 1510F in coal carbon for 45 minutes. All pieces are strong and well sintered.
I'll write more as I experiment more and experiment I will. As with the BronzClay, and then the PRO, I look forward to discoveries I'll make bumping along in territory that is not entirely known. As with everything to do with metal clay the pleasure is in the pioneering (well, at least most of the time).
I look forward to hearing about your discoveries, as well!
I'm teaching a PMC Sterling ring class before the PMC Conference this summer. The class is full but please let me know if you'd like to be on my mailing list for upcoming PMC Sterling classes.