I don't silver solder steel parts together very often but in the past I always had issues, bright just cleaned mild steel would turn black, and the silver solder would just form balls and refuse to run/wick into the join. Today was no exception - 15% silver solder - flux onto a freshly cleaned (with a file) join gradually bring the parts up to heat using a propane torch fed from a 9Kg bbq cylinder, which is more than capable of bright red heat on small parts - at the third attempt I almost gave up. I remembered I had some 45% silver solder in the cupboard so I thought I'd try some of that, however in the cupboard I saw my other jar of flux paste - this was a different brand labeled Tenacity #4 - worth a try I thought, this time I broke out the oxy torch and less then a minute after cleaning off the previous failure I had a nice neat looking silver solder joint using the 15% stuff. I don't think it was the oxy torch that did the trick as I have had problems in the past using the oxy torch, but rather the different flux paste.


Which brings me to my question - the first jar of flux paste is the one I've always used for non ferrous stuff - copper brass etc with no issues - is there different flux pastes for different metals, it would seem so to me.


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