I want to know how you are all testing the temperatures of your
molten metals during the casting process; I haven't had much luck
finding any resources on this topic.
If you melt with a torch, you do it simply by eye and experience.
The metal, when ready to pour, is fully liquid and fluid. Flux
residues on the surface sometimes are highly mobile or spinning at
certain temps. Stuff like that.
If you melt with a melting furnace, the temperature of the metal is
whatever you’ve set the furnace to achieve, within the limits of
accuracy of the furnace, and assuming you let the metal fully melt
and reach equalibrium with the crucible, etc.
More sophisticated casting machines which use built in melting
setups can simply be programmed, same as the seperate melting
furnaces, for the desired casting temperature of the metal.
If you need more accuracy or the ability to actually measure the
temperature of the molten metal, either in a furnace crucible or a
torch melt crucible, the best way is an optical pyrometer. Point it
at the molten metal and it tells you what the temperature is.