Treatment and Lifting of Two-Dimensional Footwear Impressions
Dust, dirt, mud, blood, and other substances acquired on footwear outsoles transfer with each step back to the substrate, replicating features of that outsole in the form of two-dimensional impressions. Two-dimensional impressions that occur when materials acquired on the raised out-sole tread are transferred back to the substrate in subsequent steps are known as positive or transfer impressions. A dry origin impression or mark is produced when both the shoe and the receiving substrate are dry at the time the impression is made. They commonly occur when dry shoes track across a dirty substrate and then onto a dry but relatively cleaner substrate. A two-dimensional wet origin impression occurs when the shoe outsole and/or the receiving substrate are damp or wet at the time the impression is made. When moisture is present, the impression will have a greater bond to the substrate and often includes some penetration into or absorption by the substrate.