Cleaning Glaze and Paint from Historic Poured Glass Windows

Removing dried materials from any pane of glass can be nervewracking – but especially nervewracking when that glass is hundreds of years old. Learn proven techniques for removing putty, glaze, paint and other substances from windows old and new -…

LESLIE: Don in Pennsylvania has got a question about windows. What can we help you with?

DON: These windows are mid-1700s. That’s before the Revolution. The ones I’m working on, there is – the building actually had a date on it: 1746.

TOM: Wow. That’s impressive.

LESLIE: Wow.

DON: And the glass on these was like poured glass; it wasn’t manufactured the way they make them now. And I’m trying to save the glass and I’m trying not to damage the wood at all. But I’m scraping and painting and weatherizing these windows. And the reason I’m doing that is because a lot of the glaze is falling out and the paint is flaking away and everything. But some of that glaze that’s on there – and this hasn’t been done, I would say, for more than 30 years. Because we’ve lived here 30 years and have never done it to this window.

And so that – some of the glaze is falling out but others are really tenacious and stuck to that wood and that glass. And I don’t want to ruin the glass or ruin the wood, so what’s the best way to get that old glaze out of there?

TOM: Are you using any heat to help you here?

DON: Not yet.

TOM: So, what you want to try to do is get a heat gun, which kind of looks like an industrial-size hair dryer.

DON: Yeah, I have an electric heat gun and I’ve used that to help remove some of the paint. But I don’t know the temperature of that heat gun but …

TOM: Well, you want to use it cautiously, you know. I wouldn’t lean into it with the nozzle but I would try to warm that old putty. Generally, if you warm it, it loosens up.

Now, some guys that do windows all the time will actually use steam to soften the putty. And I’ve seen guys create almost like steam chambers, where they kind of build a box, fill it with warm steam and then slide the sashes in there and then pull them out. And now they’re warm and they strip them off.

One way that you could try to do this without sort of building that chamber might be to get a wallpaper steamer. And then use some of that steam – use it against the window, warm it. That warm, moist steam may also help to loosen it up.

But if you’ve already got the heat gun, I would try trying to warm it up gently and see how the old glazing reacts to that. And if that doesn’t work, consider an architectural salvage shop for replacement window panes.

DON: Oh, OK. I will. Thank you.