Before the advent of aluminium- and vinyl-framed windows for houses, the glass panes in windows were framed with wood. In windows with multiple smaller panes, the glass sits within small ledges formed by muntins, the vertical and horizontal wood strips of the window. In addition to small metal clips, or glazing points, to hold the pane in place, a glazing compound, or putty-like substance, is applied around the perimeter of the glass. If your window has two large glass panes, the procedure is the same; only the spacing of the glazing points is different.
Remove the old glazing compound, or putty, before applying new glaze. Use a putty knife to cut the putty from around the muntins, taking care not to cut into the glass. For thorough cleaning, remove the metal glazing points holding the glass pane in place, take the glass out and continue to scrape away any bits of glaze using the putty knife.
Use the putty knife or your fingers to scoop out about a grape-size ball of glaze from the container. Warm the glaze in your hand by squeezing and rolling the ball. Place the ball of glaze between your palms and roll it into a pencil-thin strip by rubbing your palms back and forth.
Place the thin strip of glaze around the opening formed by the muntin or the larger frame. Repeat the process to cover all four sides of the opening.
Place the glass pane into the window frame and press the glass firmly into the putty. Center the glass evenly between horizontal and vertical muntins.
For smaller panes, use two glazing points per side. Lay the glazing point flat against the glass 1 to 2 inches from the corner and pointing toward the muntin. Use the putty knife to force the point halfway into the muntin. For larger panes, use at least four points per side.
Repeat Step 2 using a larger ball of glazing compound to create a thicker strip. Press the strips all the way around the pane, covering the glazing points and the edges of the glass. For a smooth finish, drag one finger along the glazing to give it a slightly concave appearance. Alternatively, the putty knife can be held on a 45-degree angle and run around the perimeter of the frame to create a crisp finish on the glaze. Remove any glaze that gets pushed out over the frame.
Glazing points can be purchased at hardware centres. Once you apply the glaze to the window frame, if it doesn't look right to you, pull it off, rework it with your hands and reapply it. Before applying glazing compound, prime the frame of the window if it was not already primed. The primer will prevent moisture penetration from the glazing compound. Apply the primer with a small brush to avoid getting the primer on surfaces you do not want to paint.
For safety, wear goggles and gloves when removing and replacing glass, as older glass may break.