(...I haven't worked in 18K gold before...I have the full
compliment of solder for 10K and 14K white... Can I substitute one
of the solders I already have or do I need to get 18K white
You will find that 18k alloys are much better to work with: Higher
melting points, and generally, less oxidization. Yellow and white,
even Nickel based alloys, are more friendly for fabrication and, as
you need, sizing. Regarding your question, before saying that you
could use either one of the solders you have available, you must
consider the following points:
Do you know, or could guess what kind of 18k white alloy the ring
was made with, I mean Nickel or Palladium based?
Is the ring going to be Rhodium plated after sizing, or is it
already Rhodium plated?
A different white tone at the soldering area would be a problem?
Does the ring has a strong enough sizing area to compensate the
weakness of a lower karat soldering?
Ideally, you should use a 750/1000 solder that has the same base
alloy (Nickel or Palladium) in order get the best joint strength,
closest color and preserving the title integrity of the piece - 18k.
But since we are talking about a repair, you may have room for some
flexibility...it means that you can use either one of the solders
you have, but I would suggest that you use the highest karat - 14k.
If you are going to Rhodium plate, the difference in color will be
hidden by the plating. Anyways, most of the "repair" solders
available, even the ones indicated for 18k alloys, are actually, low
carat solders, i.e. , 14k or so.
No matter what you decide to do, remember to protect the piece to be
sized with a coat of a saturated solution of Methyl Alcohol and Boric
Acid, specially if the piece has already a Rhodium plating. It also
helps to protect the Sapphire.
Colorado Springs, CO