Here's how to reglaze those old broken window panes. First, remove the old glazing compound with a propane torch and putty knife. Carefully remove the old glass and clean the (groove) with a soft wire brush. Apply a thin bead of backglazing, replace the glass, and gently place the push points every eight inches to hold the pane in. Apply a generous bead of fresh glazing compound and smooth it with your putty knife.
Buy a pane of glass that is 1/16 in (1.55mm) smaller that the window opening on all sides. Chip out any old putty. Clean out the recess, and paint it with primer. Lay a bed of fresh putty in the rabbet in the window frame. Press the new piece of glass into position around the edges – not in the center, where it could break. Insert glazing brads or clips to keep the pane of glass in place.