Soldering Continued

My previous post went over the absolute basics and vocabulary of soldering. But it didn't discuss how to actually solder two pieces of metal together. Or even what soldering particularly is. Let's discuss that a bit more.

Solder, as previously discussed, is a metal (let's keep talking about silver, but this can apply to gold and lead, too) that is alloyed together with certain precise percentages of copper and zinc (and sometimes tin). The finished alloy has a lower melting point than pure silver. When solder is placed at the joint of two pieces of clean metal that have been prevented from oxidizing, and then those pieces of metal are heated to the melting point of the solder, the solder will then melt and "flow" through capillary action into the joint it is closest to, and once it re-hardens, it will create a physical join between those two pieces.

Let's unpack that a bit.

• The metal pieces must both be at the correct temperature for the solder to melt and flow. It's not enough for the solder to be that temperature.
• The solder won't fill gaps between pieces. If there's a gap, what solder is infinitely more likely to do is to just flow over whichever piece it's closest to, making a mess, and not joining it to anything.
• The solution to this is to make sure that your pieces are touching.
• The solder loves heat, and it will flow towards heat. Heating the side of your piece that is away from the solder can be useful, so you don't burn your solder.
• Flux keeps your metal from oxidizing. If you do not thoroughly clean and flux your pieces prior to soldering, the solder will not flow.
• "Clean" means free from dirt, debris, and oil, including oil transferred via skin. "Cleaning" metal often means going over it with a piece of fine grain sandpaper.
• Not only do you have to get the solder to melt and flow, you must also remove the heat from the piece after the solder has flowed, to allow it to re-harden. You can overheat a piece.

Your heat source needs to be able to heat the entirety of both pieces you're joining to the correct melting point. For small bits of jewelry, this can be done with a handheld butane torch, which is what I use. For larger pieces, you can use a full size torch head on a propane tank (attached with a hose, for maneuverability), or MAPP gas canister. MAPP burns a bit hotter than propane, and propane burns hotter than butane. You can also get an oxy-propane or oxy-acetylene torch, which infuses the fuel with straight O2, from an oxygen tank. Both of these will burn very hot, and are frankly overkill for tiny jewelry projects, but absolutely perfect if you want to weld steel. They also work perfectly well for jewelry, and professional jewelers use them. For starting out, a solid little handheld butane micr-torch will solder silver just fine, though.

And last thing I want to touch on: the amount of solder you need. It's probably less than you think. Think about it this way. You want enough physical material to fill the joint of your two pieces that are touching, where they are touching. The joint should be able to be measured in micrometers, because your pieces are touching, but it might be several millimeters or even centimeters long. For reference, and to give you an idea, I used 4 pieces of wire solder, each cut about 1mm long, to attach this 8mm diameter bezel to the back plate. You can see three of them in this photo below. This amount of solder made a solid joint all the way around the bezel.

So the actual process for soldering is this:

Step 1. Clean your pieces of metal.

Step 2. Apply flux to your pieces of metal where you want them to join.

Step 3. Place solder as required for your joint.

Step 4. Gently heat your piece. The flux may bubble up if you're using borax. That's normal. The solder may jump around. Pause, re-set your solder where it belongs, and continue heating.

Step 5. The flux will change colors. That's normal. The solder will start to gently glow, and then melt, and then flow. Make sure your piece is evenly heated, and that your joint is fully, evenly heated, to draw the solder into it.

Step 6. Remove the heat and allow the piece to sit for ~30 seconds.

Step 7. Pickle the piece. The time your piece sits in the pickle solution will depend on how strong your solution is mixed, and whether it's warm or cold. Let the piece stay in until it looks clean. It will have a white cast on it, that's normal.

Step 8. Using copper tongs, remove the piece from the pickle, and place it in the neutralizing bath. It doesn't need to sit in this bath, just a quick dip.

Step 9. Dry the piece and check to see if the joint is solid.

Step 10. Assuming the joint is solid, proceed with any filing, sanding, and polishing necessary.