In this activity, students make a plaster cast of their hand or foot (Part 1 of this activity) that they can keep and use in a forensic observation game (Part 2).
Wherever we go, we leave a trace.
Our traces can provide important evidence for legal cases. Footprints, tire tracks, tool marks, and any other evidence where one object leaves its mark in another through physical contact is called impression evidence.
2D impressions (like a dirty footprint on the floor) can be lifted using techniques similar to fingerprinting. (See activities Fingerprint Fun and Fingerprint Fuming for more details).
3D impressions, however, are discovered in soft surfaces like dirt, sand, and mud, and are preserved by casting. The casting process is similar to how a dentist might make a model of your teeth: a substance is poured into the impression, hardened and then removed, creating a 3D model of the object that made the print. Investigators sometimes even use dental stone as a material for casting.