[Jewelry making - Article 00324] - Re: [Orchid] 14k and platinum

[Peter W . Rowe]

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>       Hello Leda, 	I hope someone (Peter Rowe) more knowledgable than
>     I will respond to this query. Hello All, I'm hoping to get some
>     advice mixed metals soldering. I'd like to know if 14ky and
>     platinum can be soldered end to end. 


    Judy, (and Leda), you've about got it right.  The different
    expansion rates can make keeping the joints together when you heat
    difficult.  but in addition, as a solder joint cools, the expansion
    rate difference also stresses the joint.  In some cases, it can crack
    it.  usually this will be on joints covering longer distances, and
    i've had more trouble with this in white gold to platinum joints,
    since the white gold solders are more brittle.  I'd bet the 'butt"
    joints Leda is proposing won't be a problem with expansion.  The main
    trouble is what Leda also alluded to.  The big difference in melting
    points means that while gold solder flows out onto platinum and wets
    it nicely, it doesn't diffuse into or penetrate the platinum surface
    very much, so the seam ends up as a sharp demarcation in the metal
    between two very different metals.  That can be easier to break apart
    again than one might like.  The use of the hardest gold solders one
    can use will help this, but if the bands you are trying to make are
    very thin or narrow, you might have some strength problems.  Wider
    ones should work just fine.  I'd guess if you use stock that is at
    least 2 mm wide, and 1.5 mm thick, you should be OK.  If you're
    worried, angle the seams, so it's a bit of a lap joint, not a
    straight across butt joint.  Or file a groove horizontally in the end
    of the platinum,  file th gold end to a matching wedge that fits
    into the groove, and solder it that way (think of the types of joints
    one sees in lumber, for an idea on how this works).  It increases the
    surface area of the solder seam, as well as adding a mechanical joint
    to the thing that will considerably increase the strength of the
    joint. 

Peter


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