For Your Staff:Platinum Bench
Sizing a Platinum Ring
The ins and outs of ups and downs in changing sizes
by Jurgen J. Maerz, Manager of Technical Education
Platinum Guild International USA
Many factors determine the best method for sizing a platinum ring.
As a general rule, the lowest melting point of an alloy mix is the highest
melting point of the solder used. If you have a bimetal ring, such as platinum/18k,
use a gold solder. Otherwise, the high temperature used with platinum solder
would damage the ring. In this case , the platinum portion can be sized
with a 19k white hard solder. This solder looks like platinum and the seam
can be hidden or made invisible with a tungsten burnisher and a gentle polish.
Meanwhile, keep in mind that one size equals 2.25mm or 1/10th of an inch.
Sizes or other fractions of a size are a fraction of this measurement. For
multiple sizes just multiply by 2.25.
The preferred method of sizing a platinum ring is welding. Wedge a small
piece of thin platinum sheet into the seam and weld it all the way around
using a very hot oxidizing flame. Then file the weld away for a seamless
repair. You usually can use the piece you remove from a ring when sizing
it down. This guarantees a color match and identical alloy.
A platinum/cobalt ring should be sized with 1700 platinum solder. You
can use the same wedging method outlined above. Because the ring will oxidize
slightly, wait until it has cooled or has been quenched, then dip it in
fire coat (boric acid/denatured alcohol mix) and heat to a bright orange.
Then pickle and the oxidation will be done.
It's a good idea to keep a solution of 10% nitric acid in a small pickle
pot. Soak your platinum in it before applying any heat. This dissolves many
particles of other metals that may have become attached during filing.
When soldering or welding, always wear at least No. 5 welding goggles.
If working near stones, you may have to remove them or use gold technique.
Copyright © 1998 by Bond Communications.