Matt, you're doing roughly the right thing, ie heating to the
correct temp, and allowing any red glow to dissappear before
quenching in water. As you've discovered, sterling silver simply is
not as soft and malleable as pure copper. That's the nature of the
beast, I'm afraid. Sterling is simply not as butter soft as pure
copper. Bummer, huh?
You mention boric acid and alcohol. Be aware that this trick is
generally used for gold alloys. With sterling silver, it does not
afford sufficient protection against fire scale and fire stain.
Silver must be protected with a more substantial fluxing agent than
the thin dusting of boric acid that the boric/alcohol method gives.
Your handy flux will work, though you have to be careful not to let
it burn off, which it can do if overheated. Your barely dull red
color won't do that, however, so you should be OK. Still, Handy Flux
has the problem of being a fluoride containing flux, so use good
ventillation. Personally, I'd recommend that you try Prips flux, a
mix you prepare yourself from Boric acid, Borax, and TSP (the real
stuff, not the common substitutes which are not based on sodium
phosphate. Mixed with water, and sprayed on, not brushed, it
provides very good protection for the silver. You can find more
complete discussions on the stuff in the Orchid archives. Prips is
cheaper to use than Handy flux, protects somewhat better, and is
fluoride free. But the need to spray it on for best effect can be a
bit of a pain for some people. If you get to that point, and need
additional pointers on it's use, feel free to ask me (off list in
email, I'll be more sure to see the request), including if you need,
sources for the appropriate sprayer types. Or do it the traditional
way as described in Feingold, that of "burning in" a borax coating.
Even more of a pain in the rear to do, but even cheaper to use than