MCP High Temperature Firing

Everyone seemed to want to how far the shrinkage of Metal Clay Powder would go so for my next set of tests I decided to kiln fire everything at 900 deg C for two hours as well as doing a torch firing. I threw in a few other tests as well (could I bash it, how flexible was it), and on the whole was pleased with the results.

The first piece was made from plaited snakes which took shape very smoothly and easily with a snake roller and which didn't dry out or crack while I was constructing the pendant even though I took no additional steps to keep them moist. I also cut out and drilled four pairs of graduated discs for Wabi Sabi Bell earrings, and for these the clay was rolled out to 0.75mm thick then impressed with lace.

These pieces made up the first kiln firing and the shrinkage was substantial. The pendant had shrunk 17% in length and 24% in width, while the disc diameters had shrunk by 23% for all sizes. In terms of volume the discs had shrunk a staggering 40% The picture shows the pieces after they had only been brushed (the colours on the discs are due to the lighting) and very little additional finishing was needed.

I wanted to see how well this silver would stand up to being hammered so the discs were headed for the doming block. Sadly, four of the discs (left of picture) cracked while being domed but on inspection it was evident that the cracks had occurred along lines in the lace pattern where the silver was particularly thin. Next time I'll make the discs a bit thicker if I am going to use the lace. I made another eight discs without a texture, again 0.75mm thick, and these domed without any problems.

Another project I wanted to try was a variation on the Shamrock pendant from the Art Clay Sweet Designs book. When I originally made this from Art Clay I had found it very difficult to get the individual components to stay in place while the joins dried, but I had no such problem with MCP. Made into paste with just water it seems to be quite sticky as opposed to simply wet. The high shrinkage in this instance was a drawback as the fine silver bail on the back resulted in the top of the piece being pulled forward - but it still has its charm.

The last test I did from the batch of MCP I had mixed was a simple
cockle shell pendant, made from a silicone mould I made years ago. The silver took the detail very well and again there is a fine silver bail on the back. This piece I torch-fired for three minutes and by comparing the original mould to the fired piece it is easy to see that the shrinkage was high.

I still have plenty of clay powder left to carry on experimenting, and there are still several techniques I want to try. I have never fired anything I have made from silver clay at the minimum time and temperature recommended by the manufacturers and am unlikely to start now, but lower temperatures are going to be needed for glass and some gemstones. It will be interesting to see how robust the fired clay turns out at these lower temperatures.