Hi, In my experience, it is not the size of the flask that's so
crucial but rather, what is held in the investment.
Lacy, thin objects are relatively tough to fill w/ molten metal
since, although there is not much air in the chamber (due to the
small size of the model), this air must evacuate the chamber very
quickly ahead of the incoming metal. In other words, the small mold
chamber fills very rapidly and the air inside must move out speedily.
On the other hand, a large mold cavity--like a gent's signet ring--
fills relatively slowly, because it is so much larger. Not much back
The lacy casting should have a higher flask temp when cast-- mqybe
1000 F-- since A) it is harder to fill and the metal might freeze at
lower flask temps before the mold fills and B) the fine cross section
allows the cast metal to cool relatively quickly which means that the
casting will not have excessive or coarse grain growth which
translates to brittleness and porosity.
Large mold cavities which are easier to fill can be cast at cooler
mold temps.--maybe 750 F-- and this lower temp allows this big mass
of metal to cool quickly, again without large grain growth.
Also remember that every metal has its optimum handling parameters.
Silver, although it always seems more fluid when molten, can be a
very finicky metal to cast and it is also lighter-- not having as
much inertial force in centrifugal casting or as much gravitational
advantage in vacuum casting.
Hope this helps,