Firing Stones in Sterling Silver Metal Clay

While continuing on my experimenting with sterling silver metal clay, I wanted to push the envelope some more and see what will happen if I made a hollow ring with channel set stones.

Here is my ring before firing. I made it a size 10 in hopes that it will shrink to a 7. I want to find out if the stones will take the heat. The white stones are 2mm CZs and the red center stone is a 5mm Corundum.
I made the walls thicker because the shrinkage for the sterling silver metal clay is so high. I needed the walls to hold the stones and not shrink off of them during firing. Sterling silver clay must be fired in two stages. In the first stage it is heated to 1000˚ F and held at that temperature for 30 minutes. I didn’t want to shock the stones so I used a slow heating ramp of    500 ˚F an hour. So, it took 2 hours to heat the kiln up to 1000˚ F. After allowing it to soak at 1000˚ F for 30 minutes,  I then cracked the kiln’s door and allowed it to cool. When the kiln cooled to 400˚F I removed the ring using tongs while wearing leather gloves.   In the second burnout phase, I buried the ring in activated coconut carbon with a layer of at least ½” above and below it in a stainless steel container.  I again heated the kiln up at a slow rate so as not to shock the stones. This time I ramped it up faster at 700˚F an hour until it reached 1500˚F.  I chose to ramp it hotter faster because the stainless steel container and activated carbon take longer to heat, and I wanted to know if I could go faster. When I was a bench jeweler, I re-tipped prongs on CZs and Corundum using a torch heating them up fast, so why wouldn’t these stones take a faster heating?  Since the ring has a large mass I held the temperature of 1500˚F for one hour. Afterwards,  I cracked the door allowing the kiln to cool faster. Once it was down to 400˚ F I removed the stainless steel container and let it air cool for a few minutes and then opened it. I removed the ring with copper tongs and placed it on a heat-proof surface. Once it was cool I picked it up to inspect it. (I get impatient sometimes.)
The stones survived and it came out exactly as a size 7! But take a look at the inside of the ring! As it shrank the activated carbon indented the surface! Next time I will wrap the ring in stainless steel screen!  The small round hole was put there on purpose to allow the air trapped in the ring to escape when heated. Otherwise the trapped air when heated expands and will blow a hole in the hollow area!  I had to put the hole in that area because there were pockets of trapped air in the lower part of the ring. In the top part of the ring the expanding air escaped around the stones. And as it shrank the band split in one area.  I had made the inside shank thin, only 4 cards thick and then sanded it in the dry clay stage. In my next experiment I will make it thicker and see if it cracks again.
Check out how far the metal shrunk away from the stones. This is a  photo of the unfired dry clay. Note how much the red stone is covered.	This is a photo after firing. Note how much of the red stone is uncovered after firing. Also look at the channel set stones how much more they are exposed.
Overall, I am happy with the ring. I will re-fire it filling in the crack on the inside of the ring with more clay. The texture in the inside band can be sanded smooth.