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Soldering silver prongs on copper sheet

Hello dear Orchidians, hopefully all of you are healthy and stay safe during these times.

I am experiencing an interesting problem these days. I used a copper sheet as a base plate and after finishing everything needed on it, proceeded with soldering five silver prongs on it. I chose fine silver for that. However, after pickling and polishing, when I go on to set the stone and I adjust those prongs cracks become visible at the points of inflection.

I have no idea why this happens, I took care not to put the flame on the wire and not to overheat it. To solder I’m using medium solder. Because this is fine silver I also expect it to be less brittle prone than sterling.

What do you think I do wrong?

Can you elaborate a little more about where the cracks are located or what they look like? A couple of Immediate thoughts come to mind—If they’re near the backplate along your solder seams, it could be that your solder didn’t flow evenly to both metals. If the cracks are located along the fine silver surface of the wire itself, the alloy may contain some impurities that only became visible after heating. A bunch of factors could come into play, so it’s hard to know without more details.

Soldering prongs to a flat sheet can be tricky, especially with copper and silver. Are they cracking at the solder point? Are you soldering them one at a time or setting them up so you solder them all at once? What do you mean by “point of infection”?

To make it clearer I will describe the process I went through:

  • prepare the shape of the copper sheet
  • drill holes to hold the silver prongs
  • polish tripoli silver wire (It was annealed prior to this step)
  • cut it to length
  • position it, flux it, solder all at once (one by one but same session)
  • go with rouge on the copper plate and between the prongs (this might cause some pressure on the prongs that could produce those cracks?)
  • try to bend the prongs outwards slightly
  • burr the prongs to fit the stone
  • push them back to hold the stone (cracks become visible horizontally on the wire, at the point where it bends (inflection point), they look like a dry soil (if I continue to bend the prongs a little more they break)

I considered following-

  • throwing the piece into pickle too soon (excluded)
  • I sanded the wire slightly before polishing (before soldering it) - excluded (tried without this step, same result)
  • the rouge process between the prongs after soldering? Not sure if this is the culprit
  • anything else

This is as much as I can come up with after observing different scenarios

First, fine silver is too soft for prongs. Use sterling. That alone should solve the problem. Nonetheless, cracking as you describe is 100% predictable from over bending the wire. We get only a few bends before the metal becomes brittle at the bend, or inflection site. Think of work hardening. Moving the metal around is moving it ever closer to the brittle state when cracking happens. Pay more attention to how many times the prong wire is bent at any spot while handling. Minimize any bending, try to get it right the first time as you’ll get only a couple or corrective bends before your prong becomes structurally compromised which makes it weak (brittle) and closer to cracking. Hope these suggestions are helpful.