Saturday, June 30, 2012

More PMC Sterling Silver Tests

by Janet Alexander
Technical Advisor

In my first testing last fall with PMC Sterling Silver clay, I tested embedding copper wire into the clay by trapping the ends of the wire with clay. Now I want to take this idea a little further.

Test 1 
I embedded a copper square wire and two brass round wires sticking upward from the clay instead of sideways. I had two questions:
  • Will the metal clay hold the wire after firing without the ends being held in?  
  • Will the brass attach to the sterling clay? 

Test 2
I have a Microfold Brake tool that corrugates thin metal. I have often wanted to solder sterling silver wire into the creases but never got around to it. Then I thought, what if I could use the new sterling silver clay instead?! 

So, I conducted two tests.  

Test 2A
I applied PMC Sterling Silver clay to one side of the corrugated copper sheet. My questions were:
  • Will the sterling clay bind to the copper sheet?
  • What will happen when the clay shrinks?

Test 2B
I drilled holes through through the recesses in the copper and attached sterling silver clay to both sides of the corrugated sheet. Additionally, I bent the copper into a dome.

Clay pushed through holes
Clay added to the back
  My questions:
  •  Does the sterling silver clay attach better when it grips the metal like a rivet?
  • Will a thick layer of sterling silver clay applied to the back of the copper the make piece stronger?
  • Is is bendable after firing? 
Test 3

My next test was to see how well the sterling silver clay works with PMC+. The shrinkage rates for the clays are very close. So, I embedded PMC + into a slab of PMC Sterling Silver metal clay. 

My questions:

  • Will the two clays attach smoothly together?
  • Will the PMC+ sinter correctly when its fired in carbon?
  • How will the shrinkage affect the piece?


I fired all pieces in two stages. The first stage was completed on the kiln shelf for 30 minutes at 1000˚ F. The second firing stage was in activated coconut carbon inside a stainless steel container with a lid (per the manufacturer’s instructions) for 1 hour and 30 minutes at 1500
˚ F.. I chose to fire for 1 ½ hours because I was attaching clay to metal sheet.
The Results:

Test 1
The center copper wire melted into the sterling silver clay re-alloying the metal. The brass didn't attach at all and had some signs of melting. I wondered what went wrong. In previous tests this didn't happen.

I immediately tested my kiln making sure it is firing correctly and it is firing at the correct temperature. So, the extended time, 1 ½ hours, must be the problem.

 Test 2A

The silver clay disappeared into the copper sheet! Again the two metals alloyed together.

Test 2B

The two metals alloyed into one puddle. It looks like I have a hot spot in my kiln as these were all fired at the same time.

Test 3 
The PMC + and PMC Sterling bonded fine (the inside dots are PMC+). There is a little warpage from shrinking but otherwise it looks good. The PMC+ sintered completely.

In my next tests, I will change the firing schedule back to 30 minutes and see what happens. Until next time have fun claying around!


kim said...

thanks Janet!

Roxanne (Shanghai Tai) said...

Wow, thanks for sharing your test results with us. I am so surprised that the copper wire disappeared in test 1, and that your sterling disappeared in test 2A.

Since the sterling and fine silver test came out ok, I wonder what would happen if you put some Baldwin's patina on that? Since the sterling has some copper, I wonder if it might add more contrast.

Janet Alexander said...

Hi Roxanne,
Yes, it is interesting that the square copper wire melted into the sterling and then in Test 2A the sterling melted into the copper! I think that it has to do with the shape and how the silver and copper attach to each other. In both instances, both metals alloyed together to make another metal. I would guess that the Baldwin's patina would tint the whole thing the same color.