That's worth knowing that the the flux remains active for a limited time. I've been deliberately heating the joint slowly and moving the flame around lots in order to bring more of it up to temperature in one go as I have read of other people's success with slower heating. I'm holding the tip of the torch about 2-3 inches from the joint as any closer to the hottest part of the flame results in (for me at least) an uncontrollable increase in temperature.

Maybe better technique will allow me to bring everything up to temp quickly, get the silver in, flow it round and get the torch out. I'll certainly try this out.

I may try posting a recording of my brazing efforts on youtube - I'm sure someone experienced would pretty quickly pick up on obviously poor technique!

Hmmm, maybe this is daft question (I'm no chemist), but does powdered silver brazing flux have a shelf life? Mine sat unopened for 6 years in my workshop before I got round to having a go at this framebuilding malarkey!