'Tip dip', it's normally a waxy type gel in a tin, dip the hot shroud into it and let the excess drip off and it forms a non-stick coating so the spatter doesn't stick so readily.
It's not listed in the forum shop but I know Weldequip certainly used to sell it.
Spray is ok though, a quick burst up the shroud ever now and again will do just the same job.
Hi. My local friendly fire extinguisher company will fill a mix of gas as long as the bottle (c02) has been tested