Putty Knife is a versatile tool used for a variety of tasks such as scraping, smoothing, and filling in cracks and crevices in walls and other surfaces. It is made of a thin, flexible blade that is designed to easily spread putty, caulk, and other
From Wikipedia
A putty knife is a specialized tool used when glazing single glazed windows, to work putty around the edges of each pane of glass. Putty is often applied by hand, then smoothed with the knife. Modern insulated glazing may use other ways of securing the glass to the window frame.