Watch this video from This Old House to learn how to replace a pane of glass in a door.
1 Measure the broken door pane for a new piece of glass.
2 Use a stiff-blade putty knife to pry the wooden stops from around the broken pane.
3 Carefully remove the broken pane from the door.
4 Scrape away the old glazing compound from the windowpane opening.
5 Lay a thick bead of glazing compound around pane opening.
6 Press the glass into the compound, then secure it with glazing points.
7 Reattach the wooden stops with wire brads.
8 Use nailset and hammer to tap brads below the wood's surface.
9 Scrape away any excess glazing compound.