Basic Platinum Repair Techniques-Part 3
By Jurgen J. Maerz, Platinum Guild | December 02, 2010
Platinum/ Cobalt Alloy & Annealing
The introduction of 95/5 Platinum cobalt Alloy has caused some dialog in the industry and raised some questions about just how to handle this metal. As you may or may not know, Pt/Co is slightly magnetic. This feature helps in identifying it by just filing a small stroke on a shank and then picking up the filing with a magnet. It requires care, as many jewelers use a magnet. It requires care, as many jewelers use a magnet to separate broken saw blades from filling in the the working tray and that is not feasible when dealing with Pt/Co as it will be picked up with that magnet as well.
When welding or soldering with a torch, the cobalt tends to slightly oxidize. This oxidation is sometimes so minor that it can be removed with a wipe of the finger, or, if it is more pronounced can be easily be removed by fire-coating the ring after the welding job has been completed. Then reheating it to a red and pickling. The cobalt does not oxidize until it is heated to over 1000°C. So in everyday wear, there is no reason to be concerned.
On the positive side, this great allows for beautiful castings, as it has a much finer grain and is more “wet” and thus ideal for casting applications.
Before reducing the thickness of platinum sheet or wire in a rolling mill, make sure that rollers are clean. It is possible to roll small remnants of gold or other metals into the surface of the platinum. Never reduce platinum more than 70% with annealing.
Before annealing platinum be sure the surface of the metal is clean. This can be done by pickling, steaming, or ultra-sonic cleaning. Relieve stress build-up from cold working platinum by heating the piece to about 600°C/1100°F. Softening requires about 1000°C/1830°F. To anneal, heat the platinum to a bright orange ( about 1000°C/1830°F) and hold it there. The size of the piece determines how long it needs to anneal. Annealing too long creates grain growth. If you anneal for too short of a time, your piece won’t be soft. Be sure and wear #5 or #6 goggles.
It takes about one minute to anneal a 1 mm thick, 25mm square piece of platinum stock. Quench or air-cool the piece. When picking it up with regular tweezers, wait until it is no longer red hot to prevent staining.
This technique guarantees a platinum re-tip. The soldering will not harm the stone (Diamonds, Rubies, Sapphires).
This is part three of the series Basic Platinum Repair Techniques written by Jurgen J. Maerz, Director of Technical Education for the Platinum Guild International USA