

Window stained glass overlays can be applied in one of two ways:
- direct installation onto an existing glass pane
- a separate glass pane which is installed as an insert over the existing window on the interior side
The choice of which method is best for you depends upon a few factors. Normally, overlays are leaded on both sides of the glass. However, if you have dual-paned windows, only the interior pane can be overlayed. This means that, from the outside, the design will not look quite as good. This may not be a factor if the window faces a side or back yard, but you wouldn't want to do this if your window will be seen from the street.
Overlays applied to existing windows are, of course, done on-site. The extra costs incurred with travel time and less-than-optimal working conditions, will result in a higher project cost than that of an insert. The only time you would definitely want a direct application is if the window is operable, e.g., a slider, single hung, patio door, etc.
Inserts are installed as removable panels, fitted to appear as if they were the actual window pane. The advantages are several: generally lower cost than on-site applications, not affected should the actual window glass break or, in the case of dual-paned windows, if the seal should fail requiring its replacement. Additionally, direct application of anything on the interior surface of a dual-paned window will void the manufacturer's warranty.