I don't have a resource for these; when you find one, will you post for us? BTW Do you khow what the optimum firing temp/time for medium fusing enamels on the 18 ga tiles.
Yes, I usually fire at 90 seconds and load the furnace at 1500 degrees. Heat is lost immediately because the metal and firing rack absorb a lot. Sometimes it takes practice but I look to see if the surface looks glossy. I wear dark glasses when i open the furnace.
Found exactly what I need. Tom at Thompson located some of these tiles in their inventory, and they are being shipped now. even if you do not see the item you need listed in their catalogue, just call them. they are wonderful!