Soldering is one of the most challenging and rewarding techniques in metalwork. While it is possible to work with PMC without soldering, we believe most people find that the ability to solder significantly expands your design possibilities and vastly broadens your creative opportunities. Soldering is a complex topic that you’re going to learn best through experience, but getting a grip on the basics is a great place to start and will intensify the value of your experience. Read more in this FAQ from Tim McCreight, courtesy of the PMC Guild archives.
Q: How is soldering on PMC different from soldering on sterling?
A: In many ways there is no difference. Solder flows at specific temperatures and under specific conditions regardless of the metals being joined. The biggest difference lies in reading the temperature of the metal as it is heated. Sterling goes through a specific and clear sequence of color changes. Most people who have been soldering sterling for a long time are not even aware of how closely they read these colors—at least not until they work with fine silver. PMC, like any other forms of fine silver, remains white right up to soldering temperature. Where sterling sends out signals, fine silver remains uncommunicative. The best solution (other than a lot of practice) is to work in dim lighting so that the subtle red glow of fine silver is easier to see.
Q: What kind of solder should I use?
A: Silver solder, properly called "silver brazing alloy" makes its joins inside the structure of the metal and is therefore much stronger than low temperature solders that work on the surface. Rather than say this is what you should use, I’d say it is important to design for the solder you choose. If you use a low-temp solder (say 750°F), it is important to provide enough surface contact to support the joint. Brazing alloys (often called hard solders) are preferred, but they can be a little more difficult to learn. Worth it, in my opinion, not only for strength but because they offer the best color match. Also, once a piece has been joined with a low-temp solder, it cannot be soldered with silver solder, which then makes repairs more challenging.
Q: What flux do I use?
A: This is an easy one—you must use a flux that is active at the temperature at which the solder flows. Flux is a material, typically liquid or paste, that inhibits the formation of oxides on metal as it is heated. The shorthand way to say this is that flux keeps the metal clean. The best way to ensure that you are using the proper flux is to purchase the solder and flux at the same time. Some low-temp solders are sold with flux attached or even built into the solder as a chemical core within the wire. When in doubt, put a little flux and solder on a bit of scrap and heat it up. If the solder flows into a puddle, the flux is doing its job.
Q: What about easy, medium, and hard solders?
A: This refers to three grades of silver brazing alloy: each melts at a slightly different temperature. The trick in brazing is that the entire object needs to be heated to high temperatures. When many joints are being made in close proximity (as in making jewelry), there is a risk that early joints will heat up and let go as later joints are being made. To prevent this, start with a high-temperature alloy (hard solder) and work down to easy so that successive joints are made at lower temperatures, protecting the joints made before. When using only one type, I recommend hard solder because it is easier to control.
Q: Do I need a torch?
A: Yes, pretty much. Some low-temp solders could be melted on some hot plates or on a kitchen stove, but these devices are very difficult to control. Kilns are used industrially but, for practical purposes, a torch works best for jewelry-scale work. For most applications, even a small butane torch will be sufficient.
Q: Do I need to burnish the area being soldered?
A: This is recommended for original PMC but not needed for PMC+ or PMC3 (not that it does any harm). Note, though, that mechanical burnishing in a tumbler is not recommended because the soap involved in that process will inhibit solder flow.
Q: Do I need pickle for PMC?
A: No. Pickle is a chemical that removes oxides and the glassy residue left from some high-temp fluxes. The oxides that form on fine silver do not require pickle, and flux residue can be removed with hot water.
Q: Why is there an "L" in solder?
A: The word comes from the Latin "solidus" and simply retained the "l" over time. Listen to the first syllable; British English retains the "l" sound, pronouncing the word as "sawl-der."