Solder & Flux: Mark Nelson Shares the Nitty Gritty

Learn how to choose the right solder and flux for your piece, what solders and fluxes work best together, and how to avoid common pitfalls.

Last edited: 10/28/2019

Did you know that soldering has been defined as working with temperatures of less than 800°F (450°C)? But the silver solders that jewelers use start melting (in most cases) at temperatures of over 1000°F. This higher-temperature process, which is commonly used in our industry, is technically defined as brazing. So, shouldn't our silver solders more accurately be called silver-brazing materials?

Don't worry, we're not going to change their names! But what accounts for this common misnomer? How does a jeweler know that he/she is choosing the right solder or flux for the job? There are so many confusing details related to soldering, brazing, and fluxes that we thought we'd ask our resident expert Mark Nelson to help sort things out.

Q: Mark, what's with this term brazing? Do jewelers actually talk about brazing? Why do we normally say "soldering" instead of "brazing"?

A: Well I'm not sure when jewelers and silversmiths adopted the term soldering or how it came about, but what we do is technically brazing. And to add to the confusion, we distinguish between the terms hard soldering and soft soldering. Our industry has adopted the layman's term soft soldering as the process of using low-temperature solders, or solders that melt at temperatures of less than 800°F, while hard soldering is actually brazing. Further, we use hard, medium, and easy solders. Confused yet?

solder
14K Yellow Chip Solder

Q: Rio Grande carries low-melt solders, some of which contain minuscule amounts of silver. But we also have relatively high-purity silver solders, ranging from 56% all the way up to 80% silver purity. Which one do you like?

A: It depends! Really, I like to use them all, depending on what I am doing. Some of the low-melt solders are great for just sticking stuff together or repairing costume jewelry. The bond is strong enough for light use. But if I'm creating jewelry, I will tend to go for the highest-melting solder possible. The higher the heat, the stronger the bond!

Q: I know jewelers will sometimes step-solder. Can you tell us about that?

A: Sure. When you assemble complex jewelry pieces, sometimes multiple solder joints are needed. What you want to avoid is un–soldering a joint while you are working on a later solder joint. So the best practice is to use a hard solder first, everywhere you can. Then when you need to solder again close by that joint, use a medium solder (which requires less heat to flow). If needed, you can then move to an easy solder after the medium (which requires even less heat). Using this technique, you can place additional solder joints close by previously soldered positions. Also, I try to avoid using extra-easy solder on any creation. That way, if I need to come back and repair it later, I know it's safe to use extra-easy solder on any repair.

Q:How do you select the right flux for the job?

handyflux

A: In most cases you will need two fluxes. One is a barrier flux (which is designed to prevent firescale) and the other is a flow flux (a flux designed to help the solder flow). Barrier fluxes would be fluxes such as Cupronil, Stop-Ox, or Firescoff . There are spray-on fluxes available, but a good homemade version is a 60/40 mix of boric acid and de-natured alcohol. My-T-Flux and Handy Flux are two of my favorite examples of flow fluxes. I use Handy Flux mostly for silver and My-T-Flux for gold. All fluxes are designed to absorb oxygen and prevent oxides from building up. Which in turn helps the solder to flow.

Q: How much flux do you use?

A: Enough to last throughout the soldering job. Keep in mind that the bigger and heavier the pieces to be joined, the more flux you will need. When you heat metals they begin to oxidize rapidly. We need the flux to soak up these oxides so the bond between the pieces and the filler metal can be as strong as possible. So you want enough flux to soak up all the oxides being generated, but you also don't want to use too much. Too much flux will prevent the solder from flowing, so it's a balancing act. Experience is the best teacher here.

Another thing: Flux can also serve as a temperature indicator. Each one is different, but as an example, Handy Flux becomes completely clear at 1100°F. This is a helpful benchmark to use for annealing. That process occurs in most cases around 1100°F, so when the flux turns clear you know you've hit the temperature necessary to anneal your piece.

Q: Are certain fluxes best with certain types of solder?

fluxbrush
Flux Brush

A: Yeah, over years of teaching classes and listening to other jewelers, I've observed a few general rules that might help.

  • For smaller items (say 2″ x 2″ x 2″) and for gold, My-T-Flux is wonderful, easy to use, and it cleans the seams as it heats up. It's also my preferred flux for Argentium.
  • For silver, copper and brass (especially items larger than 2″ x 2″ x 2″) I like Handy flux. It's hardier and can take the heat, so to speak.
  • Here's a tip for using Handy Flux: This stuff comes as a thick paste that can be hard to use, so I mix it in a separate container with a little distilled water to the consistency of heavy cream. This makes it a lot easier to handle.
  • Also, it really likes to dry out, and once it does, you can't reconstitute it. So I take a little out and place it in a smaller container and use that. What remains in the original container I then cover with a layer of distilled water and cap. Then I seal the whole thing in an airtight zip lock bag—I've been able to keep the same container of flux for over a year.

Q: I haven't asked you about technique. I know you teach soldering classes throughout the year. What are some of the rookie mistakes you commonly see?

A: Well, the biggest mistake I can think of is when people don't allow themselves to melt some metal. Many students are devastated when they melt a jump ring or some other element. Yes, it's annoying when things melt, but really there is no better way to understand metal than by taking it through its various phases of temperature and ultimately melting it. So melt away; just watch what you are doing and learn from it.

Q: What about cleanup? Are there any special rules about handling a soldered joint?

A: I always tell people that I am great at sanding and polishing because I am so bad at soldering. Really I just use way too much solder most of the time. So when deciding on how much solder to use, take what you think you need and then use half of that, and that should only be slightly too much. After soldering, let the item cool a little, and then quench it in water before placing it in the pickle—never quench in the pickle. It makes a mess and is bad for the metal.