Impressions such as footwear or tire tracks may be “collected” for laboratory analysis through casting.  Dental stone casting material is typically used for such casts.  Dental stone casting material emits heat while it hardens.  As such, it is not typically used for impressions in snow (sulfur is typically used for casting impressions in snow).

Water is added to dental stone powder to produce a pourable mix.  This mixture is carefully poured to cover the impression.  The material hardens, forming a permanent cast providing a mirror image of the impression.  In the images below are a shoe (left) used to make an impression in dirt (center) which was then cast (left).