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Anti flux for silver solder

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  • Anti flux for silver solder

    I'm sure that in the million-plus posts on HSM, this has been answered, but I'll never find it.

    I'm going to silver solder/braze 2 pieces together in close proximity to another piece that cannot have solder on it. Is there something that I can coat this 3rd part with to prevent the solder from wetting it?

    Thanks, Bob

    EDIT: Oh, wait ... I found it: https://bbs.homeshopmachinist.net/fo...88-solder-stop

    EDIT: Even better: https://www.youtube.com/watch?v=h-fGOKsqdmg
    Last edited by Bob Engelhardt; 08-28-2020, 10:03 AM.

  • #2
    Soot.

    -D
    DZER

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    • #3
      Yeah, I've used the soot method with success; also used the greasy anti-spatter intended for MIG guns, that works too.
      I wonder if coating with Dykem would also shield from solder ...?

      The choice will depend on whether the area to be protected can be temporarily removed or isolated to apply the soot, or whatever.
      Lynn (Huntsville, AL)

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      • #4
        Graphite pencil line.
        Helder Ferreira
        Setubal, Portugal

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        • #5
          Typewriter white-out -- paint it on. Everything washes off with a bit of alcohol afterwards.
          25 miles north of Buffalo NY, USA

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          • #6
            Put a piece of painter's or making tape where you don't want the soot. Fire up your OA torch burning only acetylene and apply soot where you need to. Peel tape and do your silver soldering.

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            • #7
              I have used "Neolube" graphite in isopropranolol for soldering front sights onto barrels, it is sold as mold release for casting lead bullets, quite similar to soot application but a liquid.

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              • #8
                I too have used White-out correction fluid for this. Works great. Paint it on and then heat a bit before soldering. The solvent boils off and it leaves a pretty effective anti-flux that cleans off without much hassle.

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                • #9
                  I used to use a paste made of alcohol and yellow ocre. Kept a tiny jar of it on my bench as i was doing a LOT of silver soldering back then. The paste kept the solder from migrating into the engraved elements of the product. It also reduced oxidation of the heated surfaces.
                  Last edited by Ironbearmarine; 08-29-2020, 05:37 PM.

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                  • #10
                    Originally posted by Ironbearmarine View Post
                    I used to use a paste made of alcohol and yellow ocre. Kept a tiny jar of it on my bench as i was doing a LOT of silver soldering back then.
                    It makes me happy to see somebody else who knows what yellow ochre is!
                    I think you could also use titanium dioxide, it maybe cheaper?
                    25 miles north of Buffalo NY, USA

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                    • #11
                      I insist, graphite pencil is all you need.

                      While goldsmiths normally strive to have their solder flow easily, there are times you don't want it to flow. Read this solder flow retardant notes for more
                      Helder Ferreira
                      Setubal, Portugal

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                      • #12
                        Use PAM or any of the non-stick sprays, like what you would spray on your BBQ grill. I use it on my MIG gun tips and it works great.
                        _____________________________________________

                        I would rather have tools that I never use, than not have a tool I need.
                        Oregon Coast

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