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Tips for Brazing/Welding Platinum

Please note: The terms “soldering”, “brazing” and “welding” are not synonyms. Soldering is the joining of two metal pieces by using filler material that melts below 450C, producing a mechanical bond only. Brazing joins metal pieces using filler material that melts above 450C, but below the melting point of the two pieces. Welding joins two metal pieces above 450C, at the melting point of the joining metals. Both brazing and welding produce a metallurgical bond.

When brazing or welding platinum, use an alumina or zirconia based ceramic brazing pad. The brazing pad should be used for brazing or welding platinum only, to help prevent contamination from residual metals. Remove the pad from the bench when it is not in use, to prevent filings, grindings, polishing compounds or ferrous materials from impregnating the pad. After the pad has cooled off, place it in a large “airtight” bag and put it away in a drawer.

Use cadmium-free karat gold solders when joining platinum to karat gold products. Cadmium can migrate into the inter-metallic grain (crystal) structure and cause brittleness. Use a tungsten solder pick when placing platinum solders on hot platinum during brazing. Platinum will be contaminated by steel picks at the red-heat stage of brazing. (Red-heat is between 550C and 700C).

Remove any gemstones within at least half an inch of the joint to be brazed or the weld area. Never re-tip prongs with a stone in place. Even diamonds will be destroyed at the temperatures required to re-tip platinum prongs. Always clean platinum in an ultrasonic cleaner, using a cleaning solution to remove oil and grime prior to brazing or welding. Some surface contamination may occur during cold-working, such as when rolling, filing, sawing, milling or grinding. Pickle the worked platinum in order to remove any metallic residue that may be impregnated on the surface.

As a rule it is recommended that when sizing a ring shank, one should weld the joining sections with the ring being sized. This can be achieved by rolling or hammering a piece of the alloyed platinum to approximately 0.25mm in thickness. Cut a pallion or chip of this flattened platinum and place between the two joining faces, letting the tension of the shank hold it in place. Cut the pallion slightly oversize so that it overlaps all four sides of the shank. This will leave a small bump after welding that can be filed down to the original surface of the shank. Using a fine tipped torch flame, weld the pallion into the existing surface of the shank.

Below are a few answers to common questions concerning brazing and welding:

Q: When sizing a platinum ring, why does the brazed joint turn black or polish out, leaving a visible line?
A: Platinum brazing filler materials, in the 700C to 1500C temperature range, do not contain platinum. They are a combination of silver and palladium. In the 1650C to 1700C temperature range, platinum filler materials can contain as much as 12% platinum. Even at 12% platinum, the remaining percentage of palladium and silver is high enough to produce oxides, leaving a dark or black line at the brazed joint. The filler material polishes out due to silver and palladium being softer than the alloyed platinum. In the event that this does occur, burnish or slightly hammer the surface to be polished, producing a work-hardened surface prior to finishing. The only time that it is recommended to use a low temperature platinum brazing filler material is when the interface is hidden or the component has been previously assembled with low melt brazing filler material (i.e. a four or six prong platinum head to a platinum shank) Four and six prong tiffany heads are assembled from two or three interlocking pieces and brazed with 1500C filler material . Therefore, use a 1300C filler material when joining these heads, to avoid re-flowing the existing filler material.
Q: What is the proper procedure for joining 18Kt gold to platinum?
A: Be sure to polish the platinum component completely prior to joining it to karat gold, to allow the karat gold to be polished after brazing. Gold polishes more quickly than platinum. The karat-gold will over-finish if polished simultaneously with the platinum component. Platinum will not oxidize during brazing/welding.: therefore the platinum finish will not be altered by the process. When joining 18Kt gold to platinum as an accent, it is necessary to protect the gold from oxidation during brazing. Do this by dipping the gold in a 50/50 mixture of powdered boric acid and denatured alcohol and allow to dry. This will produce an anti-oxidizing glaze on the gold during brazing. Use an 18Kt cadmium-free brazing filler material to join 18Kt to platinum. Use a high temperature filler material as you feel comfortable with. As in any operation, the skill of the operator determines the outcome. It is preferable to use a white gold filler material to minimize discoloration of the platinum in the event of an over-flow.
Q: Why does the jewelry item crack after joining 18Kt gold to platinum?
A: After joining these two dissimilar metals, it will be necessary to stress-relieve the product assembled. This stress results from the different expansion and shrinkage ratios of the two metals, which, if not relieved, would result in tearing or cracking at or near the interface of the two metals. Stress-relief is achieved by placing the assembled product in a furnace at 700C for 20 minutes and allowing it to cool in the furnace. Again, it is necessary to protect the gold from oxidation, using the boric acid/alcohol mixture mentioned previously. If you do not have a furnace to use for stress-relieving, you may use a standard bench torch. Using a broad, soft flame, bring the entire assembled item to a dull red (just below the melting temperature of the brazing filler material) and hold at this color for approximately thirty seconds, allowing the item to air-cool. Although this method is less consistent and predictable than the furnace method, it will help minimize cracking and tearing at the interface. It is not necessary to use this process when a small section has been brazed, only when wide or large sections of gold and platinum have been joined. Be sure to use eye-protection whenever you are welding, brazing or annealing platinum.