Sterling Silver Clay – Firing
In my last blog I covered what I thought was so great about working with sterling silver clay, now for the not so great news. As with all things, there are considerations you should be aware of as well as concessions you may need to make. And the sticky one with Sterling is that it needs to be kiln fired. If you own a kiln, then that’s great but no so much if you don’t.
And Sterling silver clay needs a more complicated firing schedule than that of its Fine Silver sibling.
The firing has to be done in two stages. The reason for the 2 step process is firstly, to let the organic binder burn away and the second to allow the clay to sinter. It needs to be in the carbon to limit the amount of oxygen getting to the clay.
Suggested Firing Schedule for Sterling PMC
The firing schedule I use was suggested by Celie Fago who was one of the first artists to get her hands on Mitsubishi’s Sterling PMC and I have tweaked after using it for some time.
30 minutes on an open shelf @ 538oC (990F) – longer if the piece is thick.
1.5 hours submerged in carbon @ 815oC (1500F)
When I submerge in carbon, the pieces are put in a small customised made box (No Flake Foil) fastened with ordinary staples. There is a layer of about 10mm at the base on which the items are placed and then covered with another 10mm of carbon. I use Magic Carbon from Cool Tools in the US, but coconut activated carbon works too and this can be obtained in the UK. If your item is delicate you might want to protect it with some kiln paper to stop the carbon granules getting stuck in your textures which can distort and mark them.
I find that once the firing is finished, the items that come out the kiln have a slightly yellowish tinge. I still haven’t worked out why this is the case and my metal clay friends have not reported this to me but there’s a simple enough solution. I pop mine in some citric acid (otherwise known as safety pickle) and hot water. Within 5 minutes they are a lovely freshly fired white. Then I polish. I have to admit, that I bung mine straight in the tumbler and polish until shiny. But the polishing rules that stand for fine silver are the same for Sterling, so polish as you would normally.
So there you have it – hopefully this has given you some insight into Sterling Silver clay and if the firing schedule doesn’t put you off, then it’s a great alternative to Fine Silver.
Until next time