No Paul, I have not tried
No Paul, I have not tried weighting the dams. I am working in a small 8″ Paragon Caldera and there isn’t much room. I’m damming on the 7″ shelf to make the largest blank I can, which ends up being 4-3/4″ square. My larger kiln is a fiber blanket model, which will only go to 1700 F.
If you are familiar with the small Caldera, the elements are in the side walls below the middle of the kiln depth and the thermocouple is above the elements sticking into the space about 2 inches. In the last experiment, I did use 1″ fiber blanket on the bottom, but then ran into an interference problem with the dams and thermocouple. The only way around this obstacle was to put the shelf on 2″ posts to get it above the thermocouple. By the time I had it all put together, I only had 1/2″ clearance below the lid, and only 1/2 clearance around the shelf for heat to rise to the glass. Since my shelf strips were right on the edge of the 1″ fiber blanket, the weight of them wanted to compress the fluffy blanket and they would roll over and off. I had to put additional support between the shelf strips and the kiln walls to hold everything in place, which further restricted heat flow. I extended my firing times through trial and error, and actually had to fire the base blank twice to get a full fuse. I used that experience to estimate the firing time for the high temperature firing time with the copper.
When this came out of the kiln, the original 1″ fiber blanket was 1/2″. That may be part of the problem. I’ve been using what I have in the shop, which are refractory materials meant for glass below 1700 F. Maybe I should have started with, and should be using higher temperature refractory materials. In my original research I did look at this and spent some time at the Zircar website. But those materials are much more expensive, not readily available, and minimum purchase quantities are way beyond the little I need right now. After talking to a number of artists who have pushed the envelope here and there in their endeavors, the consensus of opinion and experience was that the fiber blanket used by glass artisans was good for at least one firing above 1700 F. Since that is what I had in the shop, that is the choice I made.
I talked to Petra Kaiser. Same story. The Kaiser-Lee board is good for multiple uses below 1700, but it will maintain its integrity above 2000 F for one firing. Above 2000 F it does degrade and will crumble apart when the glass is removed. The Kaiser-Lee board will stick to the glass, but can be scrubbed off easily. That has been my experience with the fiber blanket. But Kaiser-Lee board is another expensive option for a one-shot use. That is why I have decided to try the Vermiculite board. It is much less expensive.
So you see, Paul, aside from trying to do the impossible, I am further compounding the problem with an inadequte kiln, and inadequate refractory materials, with inadequate financial resources, in an undersized shop space. And most folks think Don Quixote was nuts. Well…the dear Don has got nothing on me!
–Joseph 2bears, Lomita, CA