Yes, Robin. I quote from Johnson Matthey's own blurb:

"The flux residues of this product are virtually insoluble in water. Immersion in a warm (>40 ̊C) 10% sodium hydroxide solution for 30 minutes followed by brushing in a stream of water is recommended. The residues are hard and will also respond well to mechanical removal methods such as grit blasting."

It's not called "Tenacity" for nothing.

I use Tenacity 5 for everything and, although JM's advice is sound, I find that the residues will often come away just by soaking in hot water and a wire brush or scraper.

If the heating has been prolonged then they can be more difficult to remove.

I always mix Ten 5 with a drop of washing up liquid as per an old Rolls-Royce Aero procedure, maybe that helps to soften used flux. I also use meths instead of water to mix the flux because when the water boils it often removes the flux right at the point when you need it the most.

Brian

Used Borax as a flux some years ago (in an emergency). Seemed to work OK at the time, but I can't vouch for the integrity of the joint. Maybe I was just lucky.

Horses and courses again.

Borax (if I remember right) only works at red heat, using it in conjunction with low temp' silver solders doesn't work well. Good for gold soldering. OK on soldering Sterling silver, but bog standard yellow silver solder doesn't get hot enough to enter the range where borax is active.

EasyFlow Flux is suitable for low temperature (dull red heat) solders, easy to clean but exhausts quickly, and is intolerant of dirt. Tenacity solves some of these problems but is a devil to clean up. Tenacity will wet stainless steel (and some carbides), EasyFlow won't.

More complication comes when working with stuff for hall marking, and where the sequence of assembly means subsequent soldering operations, possibly at (slightly|) reducing temperatures. Easyflow won't survive being heated twice, Tenacity will.

For different grades of Tenacity, I'll defer to the maker's blurb.

Does anyone use killed spirits (zinc chloride) as a flux?

I would like to try this – Is standard pink Methylated spirits OK for the job?

Regards

Dom

It's fine. The amount of dye in meths is tiny and makes no difference to the flux.

The advantage of using alcohol rather than water to mix the paste is it boils or burns off almost the instant the flame is applied, leaving the flux to do it's job. Water takes a tad longer because it has to be boiled off before the flux activates.

My brazing experience is very limited, but my learner gut feel suggests alcoholic paste is good for smaller jobs, say up to 100g of metal, but water is just as effective above that. Getting enough heat quickly on to the job with a suitably big torch and/or insulation is probably more important than the paste fluid. Slowly cooking a joint with a small torch deactivates the flux before the silver solder is hot enough to run. The results are miserable.

Dave

It's not the time it takes for the water to boil off it is the act of boiling itself that makes the flux bubble and spread to where you don't want it, this does not tend to happen when the liquid is burnt off.