Evaluation of Staple Impressions in the Scanning Electron Microscope

Abstract

When the driving force for stapling is optimal, the desk staplers produce characteristic impressions on the shoe-ends of staples and yield regular bends of the legs of the staple to form a permanent clinch. The impression consists of persistent dents or scratches and parallel striations which appear altogether on a lifted, scraped metal at each shoe-end. The contour of this “metal-lift” is often marked by fractures and its wavy, banded shape reveals bending distorttions. The two composite impressions at the two shoe ends of a staple seldom match. This gives one many useful “individual characteristics” for comparative identification, which are solely due to the shape and the surface peculiarities of the paired slots of the clinching anvil at the base of a stapler, which force the legs of a staple to fold toward one another. The effects of pre-existing marks in the area of impression, different forms of staple and the age of the stapler (anvil) on the resulting impression, are found to be negligible. Hence, the developed method in the scanning electron microscope will be useful for forensic identification of the source of a staple on questioned documents. These studies have also laid down the foundation of a new hypothesis that attempts to explain the disappearance or obliteration of the expectant tool marks involved with bending or rotation of the driving force.