Gail, I also was a crown and bridge tech about twenty years ago–
jeweler first, then c & b and then jeweler again. I would also fuse
the surface of my crucibles into glass which worked well save for the
fact that they were Wesco type silica crucibles, as opposed to
standard clay crucibles, which I believe would not fuse.
I use boric acid powder from the drug store to cure and coat my clay
crucibles. (Silica crucibles appear to have a rougher surface and
seem to feel more bisquelike, or hard fired. They are also much more
costly than clay.) I use a rose bud tip, heat the crucible and
shower the boric acid onto the glowing crucible. Sometimes you have
to tilt the crucible to keep the fusing boric acid in place the first
time out.
Good luck, Andy Cooperman