I'd like to put a stone on a gold wire jump ring. I've been told
I can't solder the ring closed because the stone will crack.
Should we assume that you are talking about a stone bead? If that's
the case, and the ring is at least 10mm diameter, how you do it will
depend on the stone. A pearl needs every bit of protection possible,
a garnet is pretty heat tolerant.
The safest way to solder the ring closed will be to submerge the
portion with the bead in a shallow container of water and sand. The
sand serves as a "third hand" and the water cools things off. Cover
the bead with the wet sand. Your joint should be at the highest point
above the wet sand. Since gold doesn't transmit heat like silver, you
should be able to quickly solder the joint.
Someone will probably suggest using wet tissue to wrap the bead and
lower half of the wire - I've not tried that, but I'll bet it works
too... especially if you flow solder onto one side of the joint
before adding the bead. Then all you've got to do is close the joint,
flux, and heat it enough to draw the solder to the other side.
Let us know how things turn out, OK?
Judy in Kansas