Finicky iron sulphide blacks

[Josh Bernbaum]

Why are iron sulphide blacks so prone to being brittle and having a low tolerance to thermal shock? I'm curious what's going on chemically. Both Gaffer's and Reichenbach's formulas which I've used need a LOT of pre-heating and the cane I pull with them sometimes cracks during re-heating from room temp (small cane too, not just large diameter stuff). And that's in my pre-heat oven, placed in there at room temp, and before it even gets to the GH. Forget about putting cold cane into an already hot pre-heat oven like I can get away with on almost every other type of cane that's thin enough. I've noticed this often with the iron sulphide blacks cased with clear for cane. I tried annealing some cane yesterday just after pulling it and I think I thermally shocked it just by moving the still warm lengths into my annealer, which seems to be just where I touched it with the kevlar gloves. Finicky stuff.