How do I increase the metal fluidity?
If it was “spinning”, it’s fully molten, and as fluid as it’s going
to get. However, if the outside of the crucible isn’t as hot as the
area where you melted the metal first, then by the time you pour, the
cooler outside edge of the crucible could have chilled the metal a
bit. Make sure, while melting, that you’ve heated the pouring lip of
the crucible hot enough.
But 5 grams just isn’t very much. With an open faced mold, you have
to contend with normal surface tension, the same things that, when
you melt the metal, makes it ball up instead of just flowing out into
a thin sheet of liquid. You will always find, with an open mold, that
the top surface of the silver isn’t level, but curved, and the top
edges may not fully fit/fill the mold, as surface tension affects the
shape, and small quantities will make this more pronounced.
You might simply need to be melting a bit more metal, so the weight
of the metal itself forces it down into the mold, leaving excess on
top that you can file off. Or, with some sort of closed mold and a
sprue rising up, then the column of melted metal in the sprue pushes
down while the closed mold restricts the shape to the mold shape, so
once the metal is down into the mold, it has no choice but to take
the shape of the mold.