The most obvious reason to repair a window is because the glass is broken. Another common reason is because the putty has deteriorated and creates openings for air to escape, as well as being unattractive.

To completely replace the glass in a broken window you will need the following items:

- New pane of glass that is exactly 1/8th inch smaller than the destination in the sash.

- Linseed oil

- Glazier's points

- Glazing compound

These items can be found in most hardware stores. You may need to go to a glass shop for the new window pane. When measuring for the pane make sure the window is square by checking the dimensions in several places.

The first step is to remove the old pane and putty. This is easier if you apply linseed oil to the putty and wait thirty minutes. You may also be able to heat the putty to make it easier to remove. Then remove any glazier's points. You may need to break the glass to get it out. (There is a market in the art world for really old wavy glass so you may want to try to keep it in a solid piece or as large pieces as possible if it is the older glass).

Once you have removed the glass and the frame is scraped clean and is clear of all the old putty it's a good idea to wipe boiled linseed oil (you can also use kerosene) over the old wood. This keeps the dry, thirsty wood from sucking all the oil out of the glazing compound which causes poor adhesion.

The next step is to lay a bead of glazing compound on the sash to make a bed for the pane of glass to sit on. Then lay the glass on the bead and place glazier's points, every four inches, to hold the glass in place using a glazing tool or a putty knife. The points are inserted architectural hardware for glaziers into the wood firmly against the glass and should be pushed straight in and not at an angle.

Next, you will need to seal the pane to the frame by applying more glazing compound. To do this, roll some compound into a ball then roll it between your palms forming a rope that is 1/4 inch in diameter. Press this compound rope firmly along the edges of the pane making sure it adheres to the frame and the glass then, starting at one corner of the frame, while keeping your putty knife or glazier's tool at a 45-degree angle, press down hard on the glazing while drawing your knife towards the opposite corner.

You can increase the pressure by extending your index finger down the blade. Pull the putty knife across in one long stroke. Do this all the way around the window pane. You can wet the blade with turpentine or linseed oil if the compound sticks to the knife. The glazing should be firmly packed in the frame with half of the glazing on the glass and half in the frame. The window can be painted after a few days. Seal the glazing by leaving an edge of paint on the glass.