When kilnformers work with glass thicker than 1/4", it is necessary to create some sort of enclosure for the glass to prevent it from spreading outward on the kiln shelf. These enclosures are made of various refractory materials, such as metal or ceramic.
In my recent work, some of which is almost 2" thick, I found that cut up strips of mullite kiln shelves, my usual dam material, was inadequate. I had heard good things about dams made by IPS Ceramics (formerly Dyson TT) and thought I'd give them a try.
These dams are made of a very smooth ceramic material, and are available in 24" and 48" lengths. They are 2" x 1.5" in cross section, completely straight, and the surfaces are quite flat with sharp 90 degree corners. Except for the open ends, all surfaces are smooth - so they can be used with any side facing the glass, or with glass adjacent to more than one side. They are surprisingly light, because they have a hollow oval core to prevent warping and reduce thermal mass.
The 24" dams required some cutting with the tile saw to fit into my 22" kiln so I had to make decisions regarding what lengths would work for both this project, and for potential future projects, After cutting they required a prefiring according to a schedule that came with the product. After this, I applied kilnwash and let them dry. Of course, as you put your project in the kiln, you need a layer of fiber paper between the glass and the dams for additional security, and to prevent the glass from sticking to the dams.
I have been using these dams for a year now and have been quite impressed. The large cross section makes them very stable so that the vertical sides on the glass project remain quite vertical. They are easy to securely wedge into position, and have not deteriorated or crumbled in spite of multiple firings. Small sections can be cut off for kiln furniture or wedges and they work very well.
In summary, IPS Ceramic kiln dams have proved to be an excellent product and I can highly recommend them to anyone looking for quality dam material for their kilnformed glass work. They are available from Euclid Kilns. The 24" dams cost $18 each, and the 48" dams cost $36each, plus shipping.