This is something of a public service announcement. While working in jewelry repair I would sometimes see jewelry that the customer tried to repair before bringing into the shop. One of the most concerning DIY repairs was when people would take a soldering iron to their fine jewelry. A soldering iron is used on things like stained glass, circuit boards or plumbing. Hobbyists may use it on jewelry but it is definitely no place for fine jewelry.
All solder (pronounced sawder or sodder in America) is not created equal! The solder used for a soldering iron is made of lead-free (hopefully) nickel. This is often called “German silver solder,” but it is not silver and the cadmium in the nickel causes an allergic reaction in some people. Also, the color will not match yellow or rose gold. The solder will also stand out and not match when used on silver and other white metals. Even if you join a piece with this nickel solder and you don’t mind the color variation, it is likely that the solder will not hold over time. The result could be losing a valuable or sentimental piece of jewelry.
Solder for jewelry comes in silver, 14k yellow gold, 18k yellow gold, 14k rose gold, platinum and so on depending on the metal you are soldering. These solders are broken down into categories; easy, extra hard, medium and so forth and flow at different temperatures, i.e. they melt at different temperatures. These solders have melting point in the 1200 degree, 1400 degree and above range. A soldering iron only reaches approximately 500 degrees Fahrenheit, so it can not melt solder that is suitable for repairing jewelry.
Many of the DIY repairs I saw had blackened solder covering the area where the repair was attempted. There would be the tell-tale sign of blackened metal coated onto a fine, yellow gold bracelet. Generally, I had to cut away that area and it always made the repair more difficult. A jeweler who is making repairs will use the proper solder for the job. 14k yellow-gold will get 14k yellow-gold solder, sterling silver will get sterling silver solder and so on. Instead of an iron, the jeweler uses a torch. There is actually a lot that goes into a good solder.
Furthermore, the shop where I worked had a laser welder. Many times we could repair things with it that are much trickier to do with a torch. It’s worth it to check around for a local repair shop. In the end, it often cost the customer more because we had to repair their repair!