I know to cover the diamonds well with a heat shield product but I
wonder if I am taking too great a risk with this little space to
work before the diamonds
Nance, that sounds like you may be making an important mistake. You
don't need to protect the diamonds with a heat shield product. Heat
is not the enemy.
Oxygen is. You need to protect the diamonds from the atmosphere
If you simply coat the diamonds with one of the heat protecting
materials sold for insulating, you may have problems. They don't
always work. And if the diamonds get hot while covered in that junk,
they'll contact the atmosphere, and if too hot, can burn, causing the
surfaces to get frosty white (requires having the diamond repolished.
Not something you do yourself). Instead, first make sure the diamonds
are very very clean. No trace of oils or dirt or polishing compounds
or other junk. Nice clean diamonds. Then dip the whole piece in a
mix of denatured alcohol and boric acid powder (you can get small
amounts of boric acid powder just at the drug store, often sold as an
eye wash.) You need powdered form, not granules. The boric acid only
slightly dissolves, but the alcohol is a carrier, not a solvent here.
Mix it so it's a light mix about like milk. Dip the work, and ignite,
burning off the alcohol. It will leave a light white coating on the
diamonds. As you then heat the work, this will glaze over, coating
the diamonds with a boric acid glaze that protects them from
oxidation during heating. You want to also try to see that the
diamonds never get so hot that they're actually glowing. In practice,
this amounts to keeping the diamonds below around 1000F, though with
practice, you can get a lot hotter, though I don't recommend that.
After soldering, air cool till you can touch it. Never quench the
work if it has diamonds or other gems. Then pickle to remove the
boric acid glaze.
If your work has other gems, most of them are more sensative to heat
(ruby and sapphire are exceptions, but even then, not always. If
flawed, or oiled, they are not safe to heat). Most of these do indeed
need the heat sink insulating products. But for diamonds, those
products make the job harder, and are less safe for the stones.