Greetings:
Never had such a problem. Usually line my crucible with wettened
asbestos paper and do the melt in that liner - which after one or more
casting can be replaced. The actual surface of the crucible remains
clear of metal and glazing. The minute asbestos paper does not
constitute a danger to health. This solution may be primitive, but it
works for me.
Regards,
Joe Bokor
@Joe_Bokor2