Techniques
Casting of Shoeprints
Casting can retrieve a three-dimensional footwear impression. In the past, the most common casting technique involved the use of plaster of Paris. This was a messy and not always successful process. Newer and better quality dental stone casting materials and simpler casting methods developed in recent years have made casting footwear impressions easier and more successful.
Traditional methods, however, using heavy casting materials such as dental stone do not work well on a soft surface such as snow. The snow would collapse under the weight of the stone, destroying the impression. Alternative methods for casting footwear impressions in snow include sulfur casting, and the use of Snow Print Wax or paraffin wax.
Sometimes investigators will use sulfur casting to make a mold of the impression left in the snow (see photo). Casting with melted sulfur involves melting the sulfur, cooling it to a temperature just above its crystallization point, and then rapidly pouring the liquid sulfur in the snow impression. The sulfur quickly cools as it comes in contact with the snow and immediately re-crystallizes, capturing the impression. The cast must sit undisturbed for at least 30 minutes to allow the inner areas to cool completely. Sulfur casts should be handled with care, as they are fragile and brittle.
For other techniques used in Forensic Files, click here.
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