Putty is an ideal and essential tool for holding window panes in their frame. But at some point during your window home repairs, you'll likely find it necessary to remove the glass. When installing new window panes, you must remove excess putty from the glass for a professional-looking job. You must remove old putty when clearing away broken panes or removing old ones. Lucky for you, removing putty--even old, hardened putty--from window glass is a fairly straightforward task.
Apply heat to soften old, hardened putty when removing old or broken window panes. Set a blow dryer or heat gun on its highest setting. Hold the nozzle a few inches from the putty. Sweep back and forth over a 6-inch section of putty. Prod the heated putty with your finger every 30 seconds or so. When it begins to soften, you are ready to scrape it away. If you are removing newly-applied putty, skip this step.
Scrape the putty off the frame with your putty knife. Hold the knife nearly parallel to the glass frame while maintaining full blade contact. To remove excess new putty, start in one corner of the frame, and slide your knife parallel to the frame until you reach the opposite corner. When removing old putty, slide your putty knife toward the frame to wedge the knife beneath the softened strip.
Clean away the putty residue. Wipe the glass down with white spirit to remove the putty's oil residue. Then wipe the glass with denatured alcohol (do not touch the putty strip with the denatured alcohol).