Monday, December 31, 2012

Sterling Silver PMC Clay - How Thin Can It Go?

Editor's note: We leave you on this last day of 2012, with a post about one of the most exciting developments of the year. Thank you from all of us for a wonderful year!  Here's to a 2013 full of more surprises, new developments, and abundant creative energy.

by Janet Alexander
Technical Advisor

Lila Diamantopoulou sent in this request about testing sterling silver metal clay. She wanted to know if she were to make a bead in sterling silver only two cards thick and 20mm wide, would it slump upon firing and how big could she go? After deciding that 20mm was too small, I made three larger beads. The first two were flat beads 35mm x 26mm (before firing). I domed the third bead and made it 45mm x 26mm. All are two cards thick.

There were many variables that could have affected the outcome of this test. I knew that if I added a raised texture to the surface of the beads, then that would make them thicker and stronger. If I carved texture into the two-card thickness, then that would make the bead wall thinner and weaker. Along those lines, I thought about adding decorative syringe to the surface of at least one bead, but that would have added strength to it. So, I decided to add decorative elements by making a texture using scratch foam. I impressed the texture on the backside of the bead, keeping the thickness at 2mm while allowing for some kind of decoration on the bead. Let’s face it who wants a plain bead?

While designing the bead, another variable occurred to me. Do I make it a flat-sided hollow bead or domed? Doming creates strength, so I opted for domed. I wound up with three beads - one domed and two flat.

Time to fire and another variable crept up - how to orient the beads in the carbon. I knew that if I placed a bead with its widest side horizontal to the kiln floor, there would be a higher chance of slumping. Vertical placement seemed to be the better option to decrease slumping. For testing purposes, I used both placements.

Note: With the one bead on its side and the other flat, I had to move them farther apart so that I could ensure I would  only have 1/2" of carbon covering each bead. The carbon covering the vertical bead will be "taller" in the stainless steel container than the carbon over the horizontal bead. Additionally, I needed to make sure the vertical bead had 1/2" of carbon under its lowest point. 

I fired all beads for two hours, making sure to allow for ample soaking time of 1500F degrees. I fired the domed bead by itself with it placed vertically in the carbon.

The Results

I had mixed results with the flat beads. The vertically placed bead slumped inward a little on one side, maybe due to shrinkage while sintering. The other bead, placed horizontally in the carbon, slumped inward twice as much on both sides.

Little to no slumping

Slumping on both sides

But the domed bead came out just fine!

Until next time. . .


kim said...

thank you so much for sharing your tests janet, and wishing you a happy new year!

Paula McDowell said...

Janet - I think the firing schedule is off. I don't think PMC Sterling can take 1650, but I don't have me notes in front if me.

Janet Alexander said...

You are exactly right. I miss-typed. I fired the pieces at 1500F. Thanks for the catch!

Lila Diamantopoulou said...

Janet this is awesome, thank you so much! The results are pretty much as expected, but it is great to have the actual results to prove it!