Casting Three-Dimensional Impressions
This chapter explores basic casting information and discusses the materials and methods used for casting impressions in soil and sand. Three-dimensional impressions occur in exterior soft substrates such as soil, mud, sand, and snow. Most are relatively shallow but some, particularly in snow, can sink much deeper. All impressions, whether in soil, sand, or snow, are suitable for casting. The practice of casting to recover impression evidence precedes the existence of cameras. The cast captures the positive representation of the shoe that made it. Even impressions in very delicate or fragile soil can be cast if the proper procedure is followed. The compressive strength of the cast is affected, in part, by the amount of energy that goes into mixing and the method with which it is dried. Modern casting products, specifically dental stone, have excellent dimensional stability, accurately represent the size of the impression, and consistently provide information that supplements photography.