Putty is a filler material that is soft when applied but slowly hardens. It is used to fill knotholes, cracks, and other defects in wood surfaces before the surfaces are painted. Putty is also placed around the edges of panes of glass to seal them in a window sash or door.
The most common putty is a mixture of powdered natural chalk, called whiting, and linseed oil to which a small proportion of coloring agents may be added. Putty hardens because some of the oil combines with oxygen from the air and the rest of the oil soaks into the wood.
Some projects require special, more elastic putty. This type of putty is made from vegetable oil, nondrying oils, driers that make the putty harden, synthetic fibers, a powdered limestone filler, and a coloring agent.
