On older single-pane windows, the glass is usually surrounded by putty called “glazing compound,” which holds the glass in place and seals out the weather. This putty often lasts decades, but over the years it becomes rock-hard, cracks and even falls off the window. Replace broken glass while you're at it.
Considering this, do you have to paint window glazing?
Use your fingers for smoothing. The glazing must set a skin for at least 7 -14 days before you can prime and paint. The glass should be cleaned so that all of the putty oils are removed. It is important that in painting the glazing, the paint flows onto a small part of the glass to make a weather tight seal.
What is a glazing material?
Glazing Materials. A window's thermal performance is largely established according to the glazing material used and its properties. It is possible to divide the various glazing materials according to: Transparency (totally transparent or selectively opaque to various types of radiation and wavelengths)