Soldering is nothing more than connecting two metal parts together by adding a bonding agent. In this case silver solder. Together the soldered parts form a new whole.
You are going to work with an open flame, and some toxic fumes will be released. Work in a well-ventilated area and wear protective clothing. Don’t wear loosely fitted clothing (sleeves) and tie your hair back. Yes, that one comes from personal experience. Keep a fire extinguisher near your bench. Put your lighter away the moment you light your torch and don’t keep it on your bench. When you’re done, close up your gas flask. And every once in a while, check that your hoses are still in good condition. The thinner ones can get porous and leak gas.
Before you can solder, the surfaces you want to join and the solder itself have to be perfectly clean. Dirt, oil from your hands and oxidation all prevent your solder from flowing and creating a decent soldering joint.
If you have work hardened the parts, anneal them before soldering. Make sure there is no tension left in your metal: if your piece has hardened, it can open up or deform while you solder instead of closing.
And finally, it’s time to get started. Flame control is half the job. First, always touch your material with the hottest point of your flame. You can easily find it: aim the flame at your soldering block, and where a red-orange circle appears, that is your hottest point.
When soldering silver and yellow gold, don’t add too much oxygen to your flame. Oxygen oxidizes the metal and makes it harder to solder. You’re better off with a reducing flame: one where very little yellow is visible at the outer tip. Every torch is different so this might need some trial and error. With my own torch (which I highly recommend) I like to sharpen the flame and lose the yellow tip altogether. You will make mistakes and melt a few pieces along the way. That's okay. Pick up one thing to do differently after every fail and you will get the hang of it quickly.
Distribute the heat evenly. Two pieces of the same size heat up the same way. A big piece paired with a small one needs more heat on the big part. Lets say you want to add a jumpring as a bail on a pendant: warm up the pendant and add some flux, do the same for the jumpring, slide them together and keep most of the heat on the pendant, just sliding it over the jumpring now and then. Once it reaches the right temperature*, add the solder. The trick is to not overheat the pendant (the solder will flow over the pendant instead of sliding in. between) or the jumpring (it will melt before connecting to the pendant). Keep the flame moving between the two parts so they can reach the same temperature simultaneously and the solder will flow exactly in between. Remember: solder will flow to the hottest point.
Direction matters. You can use the flame to guide the solder where you want it. With silver you have to heat up everything to get a good soldering joint, so keep the flame moving around the entire piece and focus on the seam every now and then. With gold you can focus on just the parts you’re soldering together, though you should still keep the flame moving a little so you don’t burn the metal.
Flux creates a barrier on the surface of your metal, blocking oxygen from contaminating the joint so the solder can flow freely between the two metals. It will also help you to prevent fire scale. These are nasty stains that appear on silver when it’s overheated and the copper alloy in sterling rises to the surface. Those stains are very hard to remove, so preventing is better. Coating the whole piece in flux is only necessary with sterling silver (even then you can still get fire scale with too much heat). For yellow gold you only need to flux the soldering seam.
I use boraxine as a flux, a ready-made mixture based on borax. Borax also comes as a cone you make into a paste with water, or you can add denatured alcohol to boric acid. Not every material is available in every country, so ask your local supplier. And whatever you order, make sure it’s of good quality. The best part of boraxine is that it tells me when the piece is at the right soldering temperature*: it’s bubbly and white when I start heating it up, and when the bubbles disappear and it turns honey-like, I know I can add my solder. Solder can burn into your metal and create pits, or simply not flow at all if you add it too early.
There are three solders we use: hard, medium and soft (or easy). All three are an alloy of silver and tin, with the tin added to lower the melting temperature so the solder can flow before your silver melts. I use wire solder, and each grade melts at a different temperature:
The different melting points will let you build a piece up joint by joint without earlier seams coming undone. Gold solder has other melting temperatures and is made from another alloy. I decided to focus on silver here.
Use hard solder whenever you can. It’s the strongest joint, and because it contains the highest amount of silver you can’t tell the solder apart from your silver. A well made seam is invisible. But when you are making a ring with a prong setting, things change. You can solder the ring with hard solder and build up the prong setting in hard silver solder. If you then attach the setting to the ring with hard solder again, you will risk your prongs falling off and leave you in tears. That’s why we use different grades: so you can build your piece up without fearing it will all come apart.
When you add solder, make sure it’s clean. You can run over it with fine grit sanding paper. I seal mine in an airtight bag. How much to use is (again) trial and error: too little makes a weak joint, too much looks messy and means extra filing and sanding. Place your solder bits where you can still reach them afterwards for easy cleanup. If you’ve textured the outside of a ring, put the solder on the inside so you can clean the seam without ruining your design.
You can only solder where there is direct contact between the metal and the solder. The pieces should connect perfectly. When they fit tightly, the solder is pulled in between and makes a strong joint. Finish your pieces as much as you can before soldering, especially if it will be hard to reach afterwards.
If you still have work to do after soldering, quench the silver in cold water. This keeps the silver soft so you can keep shaping it (rounding it out on a tribulet for example). If you don’t need to work on your piece after soldering, let it cool by the air and the silver will harden. Before you finish the piece you’ll need to clean it, especially after using borax or boraxine, which leaves a glass like layer that can damage your tools. So drop your pieces in a pickle solution after soldering. I use vitrex, but there are others. Important: never drop steel in your pickle, and use copper tweezers to take your jewelry out.
Run through the questions: Are the piece and solder clean? Did you use flux and add the solder when the piece was hot? Is there enough heat? Did you use the hottest part of your flame? Is the whole piece up to temperature? Asking yourself these questions will almost always point you to the problem.
Most important: give yourself time to learn. I still remember my first soldering attempts. A torch in one hand, a pick in the other, just trying to get the solder to melt. It felt so unnatural, and I was sure I’d never master it. After a few tries it got easier. The worst that can happen is melting a piece, which is exactly why we start on practice pieces. So try things and see what happens. What does happen when you overheat? Give it a go and find out. Take another piece and learn to spot the signs right before the metal melts. Catch that exact moment and you’ve learned something important. What happens with no flux? How do the three solders behave under the torch? Investigate, experiment, and have fun with it.
My full video course walks you through soldering and everything else. Step by step, starting at your very first cut.