ok but how do I get it to sit in the frame permanently and without it slipping out.

Get your grandfather to cut or router a groove in the frame. Then just silicone it in place.

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Mike
"Never worry about numbers. Help one person at a time, and always start with the person nearest you." - Mother Teresa

Not an expert, but an idea: Routering a groove is probably best. If not, you could attach the glass with some of those metal clips that they sell (at the hardware store) for mounting mirrors on the wall, and put some silicone in to seal it before you tighten the hangers. I would do this on the inside of the doors, and I would over-engineer it (use plenty of hangers just to be safe).

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Amy