I make my earwires from 20g. sterling. I set up a soldering
block with wires hanging off the edge about 1/4" (more or less,
depending on the size of ball you want). If you focus the flame
toward the block, that unsupported wire-end heats up quickly and
sucks itself up just onto the edge of the block, which is when
you pull the flame away. There’s an element of timing, but it’s
pretty easy to get the hang of it. All the same size, almost
always round.
Dana Carlson