![]() ![]() The plaster is mixed with an appropriate amount of water and gently poured into the impression. One of the more common methods of recovering three-dimensional impressions is to create a cast of the impression, usually using plaster of Paris, dental stone, or a similar casting material. The light source should be positioned to give a low angle of incident light, creating shadows to provide a contrast. The application of alternative light sources can enhance two-dimensional footwear impressions. However paper and similar porous surfaces will simply absorb such chemicals, rendering the impression useless. Certain chemicals and dyes may enhance impression on surfaces such as glass or tile. The gentle application of a fine powder may develop footprints on flat surfaces. Two-dimensional impressions can often be treated in a similar way as fingerprints. Numerous techniques are available for the enhancement and recovery of footwear impressions, though non-destructive methods should always be employed first if possible. Such an impression may be two-dimensional, the print left behind on a flat surface in some deposited material, or three-dimensional, formed in a soft surface such as soil. Whenever an individual takes a step, a footwear impression may potentially be left behind on the surface. Such evidence encountered includes footwear impressions, tyre marks, and markings created by tools and similar instruments. Impression evidence includes any markings produced when one object comes into contact with another, leaving behind some kind of indentation or print.
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