How to Solder Stained Glass

This is the question I’m most commonly asked by newbies so let’s get into it!

Soldering is very challenging when you’re starting out, but it can be made MUCH more accessible with a few tricks. But first, the tools:

1. Flux: Flux is a chemical that allows the solder to find the copper on a molecular level. It cleans the surface so the 2 metals can bond well. In my trials, I found liquid fluxes to sputter too much as the heat hit them. Paste fluxes work better, but I like gel the best. I’ll typically pour a few drops into an old jar and use a metal brush to apply it to my work.
   • Getting the amount can be tricky. A little goes a long way (you should hear it sizzle when you solder, but it shouldn’t be sputtering…those burns suck, trust) but if it seems like the solder is having a hard time sticking, try being a little more generous with your flux.
2. Solder: There are 3 types of solder typically used in stained glass: 50/50, 60/40, and lead-free. 50/50 has a higher melting point and therefore sets faster and doesn’t flow as well, and it’s used for a flatter finish and decorative effects. 60/40 is favored for strength and a nice bead, and while it’s a bit more expensive, it’s my go to. Lead-free doesn’t flow well, but is crucial for stained glass jewelry and other items folks will be touching a lot. (Giving your customers lead poisoning is generally frowned upon.)
   • I generally recommend that first-timers melt a dotted line of solder blobs onto their foil line, then go back and melt them together to get a smooth solder line. When you get more accustomed to how the material behaves, you’ll be able to move iron and solder together and melt directly onto the foil line.
3. Iron: Your soldering iron should be 100W or higher. Electronics soldering irons are meant for tiny beads of solder, not the thick strip you’re laying down, and so they’re relatively low wattage. Weller and Hakko are the go-to irons for stained glass. The main difference I’ve found is external vs internal temperature control. It’s important to control the temperature of your iron so you can anticipate how the solder will behave.
   • If your temp is too high, the solder won’t stick to the tip, and you’ll “burn through” meaning the solder from the top of your project will flow through the crack to the underside. If the temp is too low, your solder will solidify too quickly, causing ripples in the solder. Temps in the 400s are most effective for laying a bead (I like 460-480F).
4. Glass: Solder will not stick to glass permanently. This is why we apply foil or came in the first place. However, you may have drops of solder fall onto and appear to stick to the glass. These will flake off with a fingernail (*once cooled, please).
   • It is possible to crack the glass during soldering. If the glass is cold, the rapid temp change from applying solder will cause a thermal shock crack to appear.
5. Foil or Lead: If your foil or lead came is old, you may find that a layer of oxidation has formed on the surface. This can be very challenging to clean off (I’ve tried a variety of solvents, and it seems good ol’ elbow grease and steel wool is the best option), so if you have old foil or came, I suggest testing a piece first to ensure solder will stick to it.

There are a few other tricks I use to make good solder joints.

First, especially when applying hobby came around the edge of your piece, hooks to hang your piece by, or when trying to get a solder line to lay flat, use little tapping motions and stop the moment you see the solder flowing to the area you’re working on.

Second, if you notice little spikes in the solder (or feel them when you go to clean the piece) that’s usually due to not using enough flux. Add a little flux, remelt the solder, and all should be well.

Third, make sure to move around your project consistently to spread the heat around to reduce the chance of glass cracks. You can always come back to fix a bad solder joint later, but if you re-melt something over and over, the heat could crack your glass.

Folks wanting personalized instruction should consider signing up for in-person or virtual Studio Time. If you’re soldering lead came, this is an excellent video from one of my favorite stained glass content creators.