The matching slumping molds are ceramic and they also have an unlimited life span if treated properly.
These molds conform perfectly with the lamp mold they were made from.
They are uniform in thickness, 1/2 inch, and are ready to go into your kiln and bend glass.
The molds when slumped into will produce a perfect fitting piece of glass onto the conforming spot on
the lamp mold;and because of the uniformity in thickness of the mold and surface quality you can sag over
the back of the mold and be very close to the shape on the conforming spot of the lamp mold. Suppose
you have a graduated stack of fused glass and now you want to bend the piece with the stack on the out side,
you need to sag over the mold. This works, I do it often. See examples