Fine silver is far more forgiving than sterling. The three ways of
telling that you have reached annealing temperature that I use aRe:
Mark the piece with a sharpie or other marker pen, when the marking
goes transparent, you are at annealing temp
Spray the piece with Prips or coat with borax flux, when it goes
from powdery to glassy, you are there (really obvious when you touch
the piece with your solder pick)
Watch the flame, when the blast over the piece turns orange you are
at temp. Something to do with the carbon apparently.
In a really dark corner you might be able to see the glow, but that
usually means you are above where you need to be, with all of the
associated large grain problems this entails.
I look forward to hearing how others do this.