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Solder Removal


RCH07

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If you put silver and gold coins into hydrochloric acid they will not dissolve but any tin or lead based solder or tin-lead alloy will.  This may leave a slight residue on the surface of the coin but it can be easily cleaned of with some bicarbonate of soda by wetting the coin and rubbing it with the bicarbonate powder.  I have done this myself.  However, it is likely that silver coins will be soldered with 80% silver based solder, which will not readily dissolve in hydrochloric acid.  This material has a high melting temperature so that electric soldering irons which only go to 400 degrees Celsius will not melt it.  Basically your only option then is to attempt to crack the braze by differential heating with a small blowtorch.  Heat the material slowly and then rapidly cool it.  Repeat this a few times and you will likely get cracks developing at the brazing interface between the silver solder and the coin.  Practise on some non-valuable pieces first in order to be sure that you do not melt the coin, although, in my experience you cannot easily melt silver coins with a mini blowtorch such as the type used by chefs.  Under no circumstances should you use electronics-style copper braid as this may form an alloy with the silver and ruin the coin.  If you can, put the brazing joint under stress as you heat and cool it so as to increase the likelihood of cracking at the joint.  Again, practise on a non valuable coin first. 

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  • 3 weeks later...

 

With all due respect to everyone here who guessed at how to remove the solder, they are all dead wrong. Do not attempt to heat the area of the solder with an iron. When coins are soldered in jewelry applications, the method is brazing and it is done with a torch or in an oven. The solder attached to a silver coin is almost always silver and is almost always hard solder, or .800fine. Soldering silver requires heating the entire piece to solder flow temperature because silver is the best conductor of heat of any metal, and heat sinking is difficult on anything other than light wire or shank stock. Removing solder from a piece of .900 fine silver whether it's a coin or a piece of jewelry should only be done by a qualified silversmith.

 

Also, be aware that heating the coin to the stage of red heat necessary for causing the solder to flow so that it can be vaccumed up with a bulb will also cause the copper in the alloy to bloom and the coin will then have to be pickled in a heated acid solution to return it to its silver color. Glazing the coin with a boric acid/ethanol solution will reduce the copper bloom, but will also have to be removed by pickling. Removing the solder is going to reduce the eye appeal of the rest of the coin which doesn't have the solder on it.

 

You should send it off to be restored or leave it alone, but trying to melt the hard solder with a soldering iron will not work and will cause discoloration.

I second this. Having worked with jewelry for quite a few years now I'd advise leaving it alone or sending it to a professional. Either way your coin will always be "damaged". Keep in mind why you want want the solder removed... If it's value, then don't bother. If it's sentimental reasons, then go for it but remember it was jewelry for a reason. Maybe the person appreciated the coin so much they wanted to always wear it?

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