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Hi Everyone,
I have a small jewelry kiln that I tried to comb pieces in twice. Both times I ruined the kiln elements and shelf because the glass ran out between the dams. It seems that the small kiln could not heat fast enough to reach my target combing temperature (1700 degrees F) and, due to the extended firing time at lower temperatures, the glass overfired. Does anyone have a COE 90 firing schedule for combing at lower temperatures, say around 1400 or 1500?

Thanks!
Ginny

You can't do it at those temperatures. The glass has to be HOT.

G's wrote:Hi Everyone,
I have a small jewelry kiln that I tried to comb pieces in twice. Both times I ruined the kiln elements and shelf because the glass ran out between the dams. It seems that the small kiln could not heat fast enough to reach my target combing temperature (1700 degrees F) and, due to the extended firing time at lower temperatures, the glass overfired.

Not sure I understand this. Most people don't dam when they comb. And if they do, then for the glass to run out between the dams you'd probably be hot enough for combing. Most small jewelry kilns heat a lot higher than 1700F; they're also notorious for having inaccurate pyrometers. What kind of kiln were you using and how hot did it say it got? If the glass flowed between dams and it was hot enough to ruin the shelf and elements, then most certainly you were a lot hotter than 1400 or 1500.

I think the solution is to fix the dams, not lower the temp. The glass won't get juicy enough for combing under 1500f, and even if it could after a very log time, once you opened it you would have a too-short working time.

Lots of options to fix the dams. The first might be to get heavier dams, or get some high-temp wire and wrap it around the outside edge of the dams to hold them in place. Either way, weight the dams at the corners to keep the glass in. You can also get a stainless steel ring or square for this.

If you cut fiber paper to fit the entire area, not just the sides of the dams, you'll stop most leak issues. Measure the side of the dam, double it, then add that measure to the length from dam to dam. Do that for both dimensions, and cut that shape out of fiber. Line the inside of the dams with it, slitting the fiber to make it settle into the corners. Overlap the fiber rather than cut it.

What you've created is a box to contain the glass.

I have had good results using the clay saucers that you get for your clay pots to use as a vessel to comb in...seems to work and gives you a round or rectangular shape. but 1500 is too low

I trust the temps on many thermocouples about like I do candy thermometers. when you think it's getting close open the kiln and check .if it's not warm enough, wait 3-5 minutes and try again. repeat until it works and make a note of what your pyrometer says. proper timing and temp is everything and it can be different for different colors of glass and different shapes and thicknesses. just like baking a cake, but use a tungsten pick in the glass and a toothpick in your cake to see when the temps are right. tips from the old guy who worked for years with no controller because they didn't exist.

You didn't say what kind of dam you are using. In a class, I have used a few layers of fiber paper strips to dam a smaller piece, and while this works well, you have to be careful about combing too close to the edges.

Dana W.

Brad Walker wrote: Not sure I understand this. Most people don't dam when they comb. And if they do, then for the glass to run out between the dams you'd probably be hot enough for combing. Most small jewelry kilns heat a lot higher than 1700F; they're also notorious for having inaccurate pyrometers. What kind of kiln were you using and how hot did it say it got? If the glass flowed between dams and it was hot enough to ruin the shelf and elements, then most certainly you were a lot hotter than 1400 or 1500.

Hi Brad,
I have a Satellite J-100. While watching the temperature, I fired the kiln just under 5 hours and it never reached (at least according to the gauge...) 1700. When I looked inside, the 2 layers of 1/8 inch fiber layers had burned away, the glass proceeded to the kiln furniture holding the fiber and then dripped out. So I was apparently much hotter than the gauge indicated...

Does anyone have a suggestion for an add-on gauge? Can it drop in through the hole in the top of the kiln?
Thanks!