Avoiding Platinum Contamination
Platinum will combine with most molten metals. While this is useful for making alloys, it can also cause you a lot of trouble.
As an example, small amounts of cadmium, lead, tin or aluminum can cause intergrannular cracking when combined with platinum. This same situation can also be caused in a reducing flame during melting, annealing or joining and liberating aluminum or silicon from refractory materials. This occurs under reducing conditions when the platinum alloy is in close contact with the support and well above red heat. Accordingly, a charcoal block would be out of the question when working with platinum. Acetylene gas should also be eliminated from any work with platinum, unless the torch is screaming, due to the fact that hydrocarbons are being emitted from the flame.
Hydrocarbons in general, such as oil ad grease are typical contaminations. It is important to avoid trapping any potential contaminant in any metal working process such as rolling, drawing, hammering, cutting or abrading.
If contamination has occurred after heating, it is “very” difficult to correct other than cutting the contaminated material out and repairing by joining in a new piece of clean alloy. In the worst case, starting over may be the only alternative. Attempts to solder intercrystalline cracking due to contamination usually results in spreading the problem. This is most common when joining gold to platinum with solders containing cadmium or when acetylene is used.
The following list highlights some possible causes of contamination that should be avoided:
- Lead-tin and gold solders containing cadmium on the same bench.
- Charcoal soldering blocks.
- Acetylene gas used for joining.
- Abrasives rolled into the surface of platinum.
- Filings from other precious or non-precious metals.
- Filings or drillings from gemstones or mineral crystals.
- Oils, greases or soaps used for drawing, rolling, etc.
- Machining suds (lubricants).
- Reducing flames and furnace atmospheres.
In general, good housekeeping will pay big dividends when working with platinum.
Make sure to check out our Jewelry Casting section for more information about our casting services. If you have any questions concerning the above suggestions, or we can help you with any piece, please contact us. We will be happy to assist you.
