What Makes Glass Crack When Soldering?

Hi Sue,

Can you please tell me what makes glass crack when soldering, as it's happened to me a couple of times and I'm not sure why?

Is it the hot solder? The hot soldering iron touching the glass or a combination of both?

What do you do when you end up with solder smudged on the glass if you can't use the soldering iron to remove it for fear of it cracking?

Thanks!
Veronica

Answer

Hi Veronica,

I assume you're talking about copper foil work.
If you hold the iron in one place too long your glass might crack. Sometimes we all have the tendency to work one area for a long time, trying to get it just right. My advice is to leave it alone and come back to it once the solder and glass has cooled. Add more flux and work on it again.

Touching the glass with a hot soldering iron, to pick up some solder that dropped on the glass, is a recipe for disaster. If you read my copper foil tutorial you will see a panel I was working on and broke a piece doing exactly that...and I knew better!

If solder drips on the glass, leave it alone until you're done soldering (this goes for both copper foil and lead work). When you're finished soldering, use an exacto knife, a hobby knife, or anything with a blade, and scrape the solder off the glass. You can usually get a point of the blade under the solder and just flip it off.

The glass might also crack if there was already a small crack started that you weren't aware of. That could have happened while you were cutting the glass or breaking it out. That is one reason I don't like tapping the glass to get it broken out. Many people whack away with all the strength they can muster up. That can cause a small fissure on the edge of the glass. Too small to be seen, but none the less it is there. When you start soldering, the heat is just enough to cause the fissure to run. I'm not against tapping, but there is a right way and a wrong way to do it. Gentle, precise tapping will get the job done with no harm to the glass. I use running pliers and only tap when all else fails.

I hope all of this information will help you,
Sue