Brazing for Platinum

Q: I’ve used an oxygen/natural gas torch to solder silver and gold and for brazing. I know that one needs the extra heat of oxygen/acytelene for welding steel—is it good for platinum as well?

A: The principal advantage to acetylene setups is their availability, ease of setup, and portability. Although the oxyacetylene flame’s maximum temperature is much hotter than propane or natural gas, the total heat output isn’t much higher. With oxyacetylene, most of the heat is concentrated at the tip of the inner cone of the flame, while the outer envelope of the flame is relatively cool. (It’s a great flame for accidentally burning holes in your gold and silver while trying to get the whole piece hot enough to melt the solder. )

With natural gas and propane, the heat is much more evenly distributed throughout the flame, and though the peak temperature is lower, the overall heating ability of the flame is just as good. Oxyacetylene can burn in a much smaller tip than oxy/natural gas or oxy/propane, making flames smaller than a pinhead possible if you need them. But acetylene tends to burn with excess carbon. As well as making the flame much too hot at the tip, that carbon will not only contaminate some gold alloys (white golds can form carbide inclusions on melting with acetylene), but it can be absolutely deadly to platinum.

Now it’s somewhat possible to work platinum with oxyacetylene if you’re always careful to use a sharp oxidizing flame with an excess of oxygen, although it’s still hotter than you need. But if the flame is at all reducing, or even neutral, that carbon contaminates the platinum, permanently ruining it. This contamination makes it brittle as hell. Most quality platinum-smiths work with either propane, natural gas, or hydrogen fuels, not acetylene. Sometimes, especially in repair work or in working with fine wires, it can be handy. But in general, oxyacetylene is better suited to shipyards, muffler shops, and the blacksmith’s studio.

Oxygen and natural gas or propane are much better and cleaner gasses for working with platinum Hydrogen may actually be the best gas for this, since it has no carbon at all. It is used in “water” torches, but the flame is hard to see, and takes some getting used to. The excess carbon from the acetylene is not all bad—it can sometimes help provide a deoxidizing atmosphere for working with silver and gold, especially when burned in acetylene/AIR torches like those made by Prestolite, Goss, or Smith. These are quite useful, and work very well as silversmithing torches.

However, few commercial jewelers, working in retail or wholesale jewelry stores, are likely to be using an air/acetylene torch. Even with the smallest tips on the Smith, you’d have a difficult time retipping prongs on a diamond ring, or doing a clean job repairing a fine chain. Perhaps with practice and enough skill you could do make it work, but it would be slower than with a tiny flame on a Little Torch or similar model. But it does make a best first torch for general hobby metalwork. The Smith air/acetylene is certainly my torch of choice for most silversmithing. The broad soft flame makes evenly heating the whole piece much easier, and avoids much of the uneven expansion and warping that can occur with larger sheet metal pieces when you try to use a very small hot flame instead of heating everything gently.

For things like silver constructions, fabrication of whole pieces of jewelry from sheet and wire, in silver or in gold, or for similar tasks, the broad soft heat from an air/acetylene torch is better than the smaller torches usually found on commercial jewelers benches. But the capabilities of that torch are much less suited to the commercial jeweler who may often be repairing existing jewelry, working around stone-set jewelry, and generally needing to get into and solder tiny isolated details on an existing piece without messing up what’s already there. A person highly skilled with a Smith air/acetylene torch can probably get it to do much of this stuff in a pinch. But it’s the difficult way to go.

If you’re going to be doing lots of soldered wire work, making jump rings or chain for example, then the Smith Little Torch is going to be far superior. Just make sure to feed it with propane or natural gas if you want to work with platinum at all. For general gold work, I guess I use my Meco midget most of all. I much prefer the Meco to the Hoke torch, which is similar. They both work with natural gas (or propane) and oxygen. I prefer to hold a torch in my left hand, leaving my dominant right hand to work with solder, pics, tweezers, etc. The valves on the Hoke are difficult to work when held in the left hand, whereas the valves on the Meco—being on top, rather than on the side, of the body—are equally reachable from either side. Also, the Meco is lighter and more comfortable, in my opinion. But it may just be that I’m used to it…

by Peter W. Rowe M.F.A., G.G.