To repair window glaze, prime a bare sash with an oil-based primer. If attempting to repair old or antique glass, be sure to wear gloves because it is brittle. Allow the glazing putty to form a skin, which usually takes 3 to 4 days, before painting it.
Make sure to have all the necessary materials before beginning the project, including a painter's tool for scraping old putty, a paint brush for priming the sash, a heat gun for softening old putty and a putty knife. Also gather glass for measuring and aluminum foil for protecting the glass from heat. Glazier's points, glazing putty and exterior primer are also necessary.