I don't know if soft solder was used in France. I know they did in the US. A friend was burning the paint off a '50s Schwinn Town And Country tandem with an air-propane torch. BTW, don't do that (burn paint), it's nasty! He stopped when he saw big blobs of lead falling on the floor. The brass fillets underneath the lead were not nearly as nicely shaped as he'd thought from looking at it painted.

Gas-welding was a thing in France, even in high-end lightweights, going back pretty far, '30s - '40s. Sorry no reference for that, just tidbits I picked up ("oral history?"), consider it unreliable. But I have seen a couple pictures of them sandblasted, where the fillet is the exact same color as the tubes. A vintage bike expert in France told me they call it "autogenous welding", and he mentioned Pitard as one of the practitioners, but he said there were many others.


More recently it has been seen as a way to make lugs, which the tubes are brazed into. Here's a shot of two Herse bottom brackets in process, from a Japanese book on Herse.

Sorry about the bad photo of a printed photo, but the text says they are welded not brazed.

The skill required to gas-weld on thin tubing is difficult to acquire. The French guys who did on bike frames came from the aircraft industry, and/or welded a lot of town bikes and porteurs before they graduated to doing it on lightweights.

Barra and a couple others even gas-welded aluminum frames, before WWII. Some broke, but some survive to this day.

Mark B in Seattle