[Jewelry making - Article 00236] - Re: [Orchid] Laser soldering & Epoxy

[Peter W . Rowe]

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>        I tried to repair a piece of 22k jewelry with epoxy and it
>     didn't work very well. I'd like to have the piece laser soldered,
>     but I'm not sure if the epoxy will present a problem - and I can't
>     find information about how to remove the epoxy.  The stones are
>     already set so heating the piece is not an option - [I could remove
>     the stones, of course, but would prefer not to.]
>
>        Can anyone help?  Can I laser solder the piece even if there is
>     some epoxy on it? If not, how do I remove the epoxy? 

    Lasers, technically, usually weld, not solder.  But that's a
    meaningless point. Just thought I say that... 

    Anyway, the lasers work with such a brief small pulse at a time,
    that the rate at which the whole piece warms up can be kept to a
    minimum if needed.  That's one of the beauties of the technology.  So
    your joint can be done with the laser with no harm to either stones,
    or the epoxy, SO LONG AS the actual joint is not right in contact
    with the stones.  There are two big limits to laser welding. One is
    that laser welding produces a weld that starts at it's widest at the
    surface, and proceeds into the metal from there.  It's more of a
    surface weld than a deeply penetrating one, with penetration usually
    not much more than two to three times the width of the weld bead at
    the surface. The deeper the weld depth needed, the wider the weld
    zone will be.  One gets around this by leaving joints fitted loosely,
    so it's a gap one can see into, and one welds it by starting to fill
    it in from the bottom, working out, with successive weld beads. But
    It's not like the invisible capillary joints solder makes, where
    solder will such deep down into a joint and be virtually invisible on
    the surface if done well.  The laser leaves a visible surface weld. 
    Done well, it's relatively small, and because it can be the same
    metal as being joined, can be fully cleaned up again later.  But
    welding two different metals together can leave a visible odd looking
    zone, and if you need to joint two pieces without disturbing either
    outer surface at the joint, it can be difficult.  There are usually
    ways around this, but it's sometimes a cause for a certain amount of
    needing to think through just how one is going to make the joint. 

    The second thing to understand about laser welding is that the
    energy is in the form of light.  Infrared, actually.  And like any
    light beam we can see, that hits a nice reflective metal surface, the
    vast majority of the beam just reflects off.  The welding with a
    laser is done by the small amount of the energy that is absorbed, not
    reflected.  With 22K yellow gold, this is generally likely to be
    something like 2 percent of the energy of the beam.  The other 98
    percent reflects off.  It is diverging rapidly, and a short distance
    from the weld, it just enough energy to sting a little if it hits your
    finger.  But right next to the weld, it's still a pretty hot and
    intense beam of infrared.  And that's where the risk to stones comes
    in.  If the joint must be to metal that is actually in contact with
    the stone, and that metal is thin, then if the beam burns through,
    during welding, or if, as it reflects off the metal it then hits the
    stone, stones absorb much more of the energy.  Diamonds, at lower
    settings of the laser generally can survive this, since they're
    highly transparent to infrared (so it just goes through), plus they
    conduct heat so well that it dissipates before doing damage.  Higher
    settings will burn a diamond, and most colored stones simply cannot be
    allowed to be hit by any level of the laser or it's reflected beam. 
    This does make some limits to what can be repaired with the laser. 
    prong tips, thin bezel edges, and the like, can be difficult on
    colored stones.  Often, there's still a way, but it can be dicey. 
    Still, the beams are very tiny, as are the welds, so these limits
    generally apply onto to quite thin metal, or joints literally right
    in contact with the stone (like a crack right at the upper edge of a
    thin bezel, for example.    Other than these scenarios, laser welding
    is remarkably versatile, and should be able to do most repairs you
    can imagine with your piece 

    As to removing the epoxy, the commercial product, "Attack", a
    solvent of mostly M.E.K.,  usually does a fine job.  Beware of using
    with any stones that may have been oiled or treated with resins (like
    emeralds), since it sometimes will remove THAT too... 

    If you need help with the laser joint, feel free to contact me. 
    I've got one at work, and another in my home shop.  Prolly cost you
    mostly just postage, as the welding itself is quick and easy in most
    cases.  (and I'm cheap...) 

cheers
Peter Rowe
Seattle

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