Doc, just what did you do? If you laser welded or PUK welded the
shank, and are now faced with “smoke” from the welding (black fumes
deposited on the diamonds, but the diamonds are OK underneath this),
then you need not go so far. Heavily coat the diamonds with ordinary
boric acid firecoat first, then more soldering flux (Batterns works
fine, or any of the paste fluxes.) Then gently heat until the flux
liquifies. Heat to “just-barely-glowing-in-a-dark-room” sort of
temperature. The flux will lift off that metal vapor that condensed
on the diamonds.
If, on the other hand, you torch welded the platinum, and the
diamonds did not get coated with metal condensate, but instead, got
hot enough to burn the surfaces (and now look white and frosty,
instead of blackened), then you too are cooked, figuratively. Acid
won’t restore the polish to the diamonds. You’ll have to replace
them. By the way, if that’s the case, and you have trouble with the
bead set prongs, someone with a laser welder or PUK welder can
easily restore them without damage to the diamonds.
Oh, and HF won’t dissolve a platinum vapor film very well either. It
dissolves silica just fine, and does a number on your lungs, and all
that stuff. But it won’t much help your cooked diamonds, if indeed
they are heat damaged. If only coated, then HF is more than you need,
and dangerous stuff too.