How do I know if the leaded windows in my home are original?

A lot of homeowners in Toronto's older neighbourhoods have leaded glass and aren't sure whether it came with the house or was added later. It's worth knowing. Original glass has real value and it changes how I think about restoration.

Look at the glass itself

Pre-1940s glass was made by hand, either blown or drawn, and it shows. There are slight distortions, ripples, and variations in thickness that you can see when light moves through it. Hold a straight edge up against the glass and look along it. If the line wavers a little, that's old glass. Modern glass is flat and completely uniform.

Old clear glass also tends to have a faint cast to it, sometimes slightly green, sometimes amber or grey. That's from the minerals in the original batch. It's different from modern clear glass, which is essentially colourless.

Look at the lead lines

Original lead came is heavier and less uniform than modern machine-rolled lead. The solder joints have a handmade quality to them slightly irregular, sometimes with small variations in the surface. Modern re-leads and reproductions tend to look cleaner and more consistent. That consistency is actually the tell.

Look at the putty

Original windows were set with linseed oil putty that's had decades to harden. If the putty around your lead lines is rock hard and slightly darkened, that's age. Newer windows or re-leads have softer putty that hasn't fully cured yet. You can usually feel the difference just by pressing gently near a lead line.

When you're not sure

I can usually tell within a few minutes of looking at a window whether it's original, a reproduction, or a more recent installation. If you're buying a home and want to understand what you're actually getting, it's worth having someone look before you close.