I vacuum cast and use an electrolmelt to melt the metal. I pour
silver into a 830 degree flask and a 1000 degrees flask for 14K
I read someplace that you can tell if the mold/metal temp is correct
by looking at the top of the sprue. The temperature was correct if
the top is flat. If the top is concaved the temp combination was too
cool. If the top is bubbled up the temp combination was too hot.
I once cast sterling sterling into a 1000 degree mold following
someone’s suggestion. The sprue blew up like a balloon.
I cut the sprue in half. The inside looked like a sponge.
The flask temperature stays. fairly constant during the
vacuum/electrolmelt process because the flask is removed from the
oven and metal is poured almost immediately. The flask temp during
centrifugal casting may cool considerably before themetal is melted
John had it correct. Metal/mold temp, metal composition, dirty/ old
investment and water make up and temperature can all affect the
casting process. On top of all the different procedures the casting
gremlins may decide that they don’t like you and screw up a
perfectly good process. LOL Good luck in correcting your casting.