How to identify if a rod is "Silver solder"

[CambridgeWorks]

As title. I have some rods (a bit like uncoated brazing rods i appearance) all are silver-ish in colour. The thin ones (18swg approx) I know are silver solder from years ago in my refrigeration repair days. They are quite shiny as well, without cleaning. However, the thicker ones (12swg? approx) came from a VHF/UHF home brew enthusiast amateur and I do not know their pedigree. They appear a bit harder when filing and are not as bright in their uncleaned state.
There may be a clue, as these thicker ones have what looks like paint (green) across each end. Any ideas if this is a code for a different silver solder alloy?
I do appreciate there are different % grades of this material as well. I am not an expert by any means.
IF it is all silver solder, I am looking to donate it to a very worthwhile heritage railway cause.
Thank you in advance, Rob

[mole42uk]

Are you sure they are solder, not stainless steel?

[alanworland]

Might be worth trying a piece on some fluxed brass/steel?

Alan

[CambridgeWorks]

Thin rods are definitely silver solder, I used them decades ago. None of these are anywhere near as hard as stainless steel.
Unfortunately, I only have a gas hob to heat test with! Not tried this, as silver soldering decades ago I used oxygen/propane for sufficient heat source.
It is the Green painted code I am hoping may jog a memory?
Rob,

[Mr Moose]

Hello,
If it is old silver solder it may well contain cadmium which is now banned in Europe in solders (there are a few specialist exceptions) so if your railway heritage is a corporate body they should not use it unless they are sure it is cadmium free.
http://www.hse.gov.uk/pubns/eis31.pdf
Yours, Richard

[CambridgeWorks]

OK Richard, a bit like our hobby and our lead solder. Such is life!
Thanks, Rob

[mole42uk]

We use three grades of silver solder at work, none of which have a green identification. The solders probably also contain all sorts of banned chemicals, but we are used to that! We use tin/lead solder every day as well.

[Diabolical Artificer]

Rob, scratch the surface and put a drop of acid on it - silver goes red. Vinegar may do at a pinch but best to use the strongest acid you can lay your hands on. Obviously don't inhale the fumes. Also silver solder is heavy and less flexible and takes more heat to get it too melt.

Andy.

[CambridgeWorks]

OK Richard, I retired 4 years ago and sometimes H&S concerns were not fully dealt with when raised!

Andy, I tried with some acid flux, as used for ordinary soldering. No effect on any of them, so probably too weak. Unfortunately, days are gone when you had screw top cells on car batteries and a hydrometer to test. I will continue looking....
Thanks both, Rob

[Diabolical Artificer]

You used to be able to get quite concentrated hydrochroric acid from the chemists if you asked the pharmacist nicely, probably not the case now. You can also send off for silver testing kits, which is basically acid in a tube.

Andy.

[dseymo1]

Hydrochloric acid is availale from builders' merchants as 'brick cleaner' (perhaps not for much longer, though).

[CambridgeWorks]

Thanks both of you.
I think I will let them have it and decide for themselves.
Rob

[WME_bill]

Silver solder.
I am afraid I use heat to decide. Though a squeeze with jaws of pliers will tell you. If soft and marked, the soft solder tin/lead., If hard and little marked, then silver/brazing.
Standard 60/40 tin/lead melts at 200C, these new non lead solders higher. The Weller iron bit is around 380C. If the soldering iron does not melt it, its probably silver based.
There are lots of silver solders, but they all start melting between 600 and 700C.
I use Easy-Flo, at 620c, and an unknown brazing strip which melts higher. Both unmarked.
Look at the use.
They generally turn up on the tags to high power mains dropper resistors in compact radios. The tags are silver soldered to the lead in wire. And on Morphy Richards iron timing elements.
Very useful for nichrome also. Borax is the usual flux. I find a butane/air blowlamp very convenient.
wme_bill

[Radio Wrangler]

You've just got to prepare a test joint, get it hot and fluxed and try the stuff out.

It used to be easy for me when I had oxy-acetylene equipment, that could easily make the temperatures required and in a fairly tightly focused way. Brazing and silver soldering were just a matter of employing a larger but lower pressure flame than for welding, with a little surplus oxygen and watching surface tension doing the job.

Since I changed over to Tig/Argon I've got even higher temperatures available and the amount of power can be varied over an amazing range, but the arc attachment makes the heat very focused and it becomes difficult to heat the parent metal without melting tracks in it. Overheating a tungsten with a burst of reverse polarity to make a ball end on it helps, and then running with an excessive arc length is the best I can do, the rest comes down to rapid torch movement to keep the arc on the move.

Silver soldering with a propane torch is difficult but in the opposite direction. The heat is pretty diffuse and it's hard to get the joint area to temperature without making a lot of the surrounding area equally interesting to the solder.

A propane/compresed air torch may be the easiest tool for silver-soldering, but they're fairly thin on the ground. Maybe Mapp gas would be good?

David