I rebuild one of my 1902 double hungs each year. The glass in my sashes is puttied on 3 sides. The top piece of the sash has a dado groove that the glass slides into. I have never been able to remove the pane without breaking it and the trouble always occurs with that dado. Anyone know a special trick for this. Single strength glass is cheap enough, but the old wavy glass is sort of cool.

 

You have to be ultra careful, and it still may break. The Dado has a small bit of glazing in it, which is probably what's breaking the glass. Once you completely remove the glazing from 3 sides and remove any glazing points, you can tap the outside edge of the sash lightly with a hammer and block of wood... (parallel to the glass, not perpedicular to the glass!) this will usually jar the glass loose from the dado and you will feel that it's able to wiggle around side to side and up and down. Don't force the sash out of square by racking the corners... that can also break the glass. And missing just one glazing point is a sure way to break the glass as well.

Once its free, you need to lift the glass ONLY enough so that it clears the glazing rabbet... then pull the glass out of the dado... but don't raise the glass too high, that's when it will break. Keep it as flat as possible.

 

Thanks, X. I broke the lower glass today, but tomorrow will attempt the upper. Sounds like you have done this before. This is a nice thing about retirement, I have 80 spare hours to mess with a single window.

 

Breaking the glass is the fast way to get it out.