As you see in my photo, I had it sitting on an 18" tile, which was on top of a wooden, painted table I had on my porch. I had read many posts online, and several said as long as it was on a ceramic tile, it would be fine.
For my first attempt, I started with PMC3 clay, which is a low fire fine silver clay. I fashioned a few little teardrop shaped charms and used a stamp to put a texture on it, added holes for connecting, and fired it at 1600 for about an hour. They came out properly sintered and everything went fine. That was a few weeks ago.
Last night, I decided to try the copper clay and see how it fared. Things weren't quite as smooth this time around.
My husband and I made 7 pendants and charms with the copper clay. We let them dry a few hours, and they were leather hard, as the instructions said they'd be. I decided to be safe and do the 2 step firing, even though I didn't have intentions of enameling. The first mistake I made was misreading the firing temperature, and I only took it to 500 for the first fire, when it said to go to 560. I don't know if that caused any issues or not, but after the first fire, which was directly on a raised ceramic shelf, the pieces were intact and fine and felt hard. I removed them and embedded them in activated coconut carbon in a stainless steel firing pan. The instructions said to put the pan on stands, but the stands plus the pan combined were too tall for my kiln to close, so I had to put the pan directly on the bottom. I had about 1-1.5 inches of carbon on the bottom, the placed the 7 pieces in the pan, with space between them, and filled up the container the rest of the way with the carbon. It seemed pretty packed full when I put the lid on.
The firing instructions for the 2nd fire say to take it full ramp to between 1700-1800 degrees and hold for 3-3.5 hours. I ramped the dial to a 6 to get the temp up. Keep in mind there are no digital settings like an oven, just a dial that goes from low to high with 6 numbers between. The max temp is supposedly 2000 degrees, so I figured that was a good place to start. I got the temp in the range it should be, cut it back to 5, and walked inside to work on something else. I checked on it periodically, every 10-20 minutes, but at some point I must have waited a good 20 minutes, and when I went to check on it, the temp was at 1860. I immediately cut the kiln down to low to try and cool it back down. At this point I get distracted again, because while standing there watching my thermometer, it adjusts very slowly. It isn't like it immediately cools or heats, it takes considerable time. It took an hour or so to even reach the 1700 degree temp. During this second distraction, the kiln gets below 1700, so I freaked out again and ramped it back up, deciding that this time I would stay with the kiln for the remaining duration of the fire time. I got the temp back between 1700-1800 and was keeping it there fine...then I started smelling smoke.
Initially I thought it was my thermocouple, which really isn't made for such high temperatures, but seemed to be functioning fine even though the wire was glowing red hot when I would take it out. The protective sheathing had burned away completely, but the wire was still working. The smoke was not from the wire though, it was from the wood table that was under the tile and kiln. I felt the table and it was quite hot, and obviously burning since I could smell the burning wood. After closer inspection, I notice that the tile under the kiln has cracked and separated. At this point, I begin to panic.
The kiln is heavy. It is large, ceramic, and was running at 1750 degrees. I do have fire retardant gloves, but even with those on, I could not pick up the kiln without it hitting some part of my body or arm. There was just no way to move it while it was hot like that without severely burning myself.
I raced into the house and grabbed a 12x12 ceramic tile we use as a work surface for polymer clay and brought it out. Using my gloves, I lifted the kiln enough to push the broken tile together where it had broken apart, lessening the opening where it was cracked, like fitting a puzzle piece together. I then wedged the new, small tile underneath the kiln to add another barrier and lift it higher, and grabbed my fire extinguisher just in case the table went up in flames. I also turned the kiln off for a few minutes during this whole process, just because it was my initial reaction to turn off the heat source, though it takes hours to actually cool down, so it was kind of pointless. I took a sponge to the bottom of the table, ran water into the cracks of the tile, and basically tried to wet any area that was exposed and hot that I could reach around the kiln. I then turned it back on. The temp was measuring above 1600 when I turned it back on, so I knew I hadn't lost that much heat, and I continued the last hour of firing with a hope and a prayer that my house wouldn't burn down, and managed to keep it right around 1750 for the last hour.
Once it had been going for 3.5 hours total, I turned it off and waited until it cooled off before going to bed. After waiting well over an hour, it was still only down to 800, so I used a screwdriver and propped it open barely - less than a quarter of an inch, to slightly speed up the process. When it was down to 500 and the table was clearly much cooler, I went to bed. At this point it was 6:30 in the morning.
I woke up around noon and inspected things closer, and unfortunately, only 2 of the little charms I made survived. The larger pendants had broken up into pieces and turned to dust when I tried picking them up, but my small ones sintered fine. They are extremely small. There is a shrinkage that occurs because the clay part of the compound dissipates and leaves only the pure alloy, which then sinters into solid metal. I believe this is usually around 20%...but mine look like they are at least 50% smaller, or even more. I tried breaking the little pieces and they are sturdy. Here are the 2 pieces, and part of another, that survived and weren't dust. Its blurry, but you get the idea. Basically they turned into small tiny scraps, except for maybe the middle one, which I suppose I can use as a tiny charm in some earthy design.
Now for the really fun part...here is what the tile that cracked looks like now.
And here is what the stainless steel pan looked when I took it out of the kiln. It was brand new and shiny when it went in. The top is all rusted and weird and left metal shavings and dust everywhere - I have no idea if this is normal or not.
And here is what my table looks like when I finally moved the broken tile and kiln out of the way. Whoa. It split the table completely and totally cooked it. I'm lucky I didn't burn down my house or myself. Clearly the large tile I was using wasn't enough, or maybe it wasn't ceramic. I honestly am not sure. My apologies to my sister, whose table this actually was, and who took the time to paint it...oops.
So obviously my first attempt was a total failure and a comedy of errors that I hope to avoid next time. There are a few things that could have led to the demise of my pieces, and I'm not sure if it is one or all of them. I hope someone who knows what they are doing will be kind enough to share some tips or insight, so I don't waste all that clay making the same mistakes again. In the meantime, I believe I will just work with polymer clay today. : )