I have read a good number of the postings on flask temperature, but still the picture is not perfectly clear. Why is it that I have been able to cast a perfectly dense 3cm by 3cm by 3mm slab of silver with raised initials (2 to 3 mm high) using a cuttlefish bone at ROOM temperature, yet if I want to use a flask it should be seven or eight hundred degrees Fahrenheit?? (None of the books I have purchased address this topic.) There must be a simple answer, but I cannot think of it.
Ill try to give a simple answer.
Using a cuttlefish bone you can cast at room temperature because the
cuttlefish walls are thin and absorb the heat very quickly.
Not so with flask investments. At room temperature, the metal will
solidify before it gets into all the cavities.
The correct flask-temperature for each cast can be a problem to the
novice. You can be guided by many books, but only experience will
Mitch Altman puts it this way: “The best flask temperature is the
lowest possible while still achieving a full and complete filling of
the pattern cavity”.