To solder or fuse, that's the question! Literally. It's a question that my students ask quite often. Since fusing and soldering are high on my list of go-to metalsmithing techniques, I want to share some of my observations with you and discuss the differences and the merits of each method.
Soldering involves joining metal using an additional metal alloy called solder. A small bit of solder is placed on the join and heated using a torch. As the solder melts and then cools, the metal is connected at the join to form a solid bond. Copper (even though it is pure), sterling silver, brass, bronze and gold filled are soldered in this way. However, heating these metals forms a layer of cupric oxide, known as firescale, on the surface. This needs to be removed with an acidic solution (called pickle) or by filing and sanding before additional soldering can be done on the piece. This is time consuming but necessary for soldering.
Fusing is a little different. This technique requires the use of pure metals, pure or "fine" silver and 24Kt gold, not alloys. No solder is needed to join (fuse) these two metals to themselves. This time the torch is used to quickly melt the metal, and it joins (fuses) as it cools. Since the metals are pure and contain no copper (the culprit of firescale), there is no discoloration and the metal is as shiny as it was before it was heated with the torch. No pesky pickling is required.
Now let's compare fused and soldered pieces to see how they differ.
This is fused chain. Fine silver is great for making chain, as it is soft and easy to shape. After fusing a ring, the metal seam disappears, so no filing is required. Work can be done rapidly as you don't have to stop and clean your piece before proceeding to the next step. And after the finished piece spends 20 minutes or so in a tumbler, it's shiny and becomes work hardened.
One drawback is getting fine silver to fuse without leaving a tiny lump at the join. Molten metal flows and follows the heat of the torch, so sometimes if the flame lingers in one place, the molten metal can pool at that spot and cause the lump.
Now check out these soldered rings, below. Since they are made of sterling silver, copper and brass, they cannot be fused. If you want to work with metals other than fine silver and pure gold, soldering is required.
Next, let's look at a couple of pieces that I fabricated with fine silver and soldered rings.
You can see the rings with copper wire solder set and ready to go . . .
. . . and the post soldered version with the rings intact and sturdy joins.
Both the soldered copper and the fused fine silver pieces look great; one is organic (fused fine silver) and one has cleaner lines (soldered copper). In the comparison below, you can see how they look after hammering. These are ready to incorporate into a piece of jewelry.
So, let's sum up. Fusing is best used for making rings and chain. Components can be made with it, but remember that you'll get a "melted" look where the pieces connect together. Fusing only works on pure metals and has the advantage of being firescale free. It should be work hardened in a tumbler to add strength.
Soldering is used to fabricate all types of metal components. You'll need to apply solder and flux before soldering, and after it spends time under the torch, you'll need to pickle (or file and sand) the piece to remove the firescale. The resulting pieces have clean lines and (hopefully) no melted metal.
I hope you'll enjoy experimenting with fusing and soldering as much as I do. Both methods come in handy and produce great jewelry components. –Kate
Learn all about soldering with Kate in her new book, Simple Soldering!