Shine your UV light on the crack for 2 minutes. If you're using the sun, cover the rest of the window with cardboard and leave the crack exposed for 10 minutes.
For three weeks, I lived with the crack. I told myself it was "character." I told myself it added "thermal complexity." In reality, I was avoiding the four horsemen of home repair anxiety: Is this fixable? Do I need a new window? How much will this cost? Can I really do this myself? how to fix a cracked house window
You didn't weld the glass. You filled a void. Under thermal stress (a hot summer afternoon after a cold night), that crack can still propagate. The resin is a bandage, not a resurrection. Shine your UV light on the crack for 2 minutes
Place a piece of painter's tape along the bottom of the crack. You are creating a tiny shelf. Then, tape a small "channel" at the top of the crack—a little funnel made of tape where you will inject the resin. I told myself it was "character
So clean the glass. Inject the resin. Cure it in the sun. And then, when you finally stop seeing the repair, you’ll remember that the purpose of a window is not to be flawless—it is to let the light in.
My crack? After the resin cured, it was 90% invisible. You could only see it if the low winter sun hit it at exactly 4:00 PM. For two years, it held. On the third year, a new crack branched off from the old one, like a tributary from a river.