I just found the reference to bronze welding that I thought I had. Philip Irving, the great motorcycle designer describes it thus; ".... bronze welding in which the filler rod material instead of being mild steel is a copper alloy known under the trade name of Sif-bronze. This is applied with an oxy-acetylene torch but owing to its low melting point the heat required is less than for true welding; the torch is fitted with a larger tip and the flame adjusted to give a less intensity of heat spread over a larger area.,,, considered by... the makers of the tubes... to be kinder to the steel... also the bronze supplies a ductile joint between the tubes so helping to relieve any stress concentration." He goes on to explain that because it passes through a semi molten stage it can be used to build up fillets and bosses. The heading for the section is 'Bronzing'
Stuart Tallack in Sussex