NCJ Number
204665
Journal
Journal of Forensic Identification Volume: 54 Issue: 2 Dated: March/April 2004 Pages: 158-169
Date Published
March 2004
Length
12 pages
Annotation
This article discusses the use of expandable polyurethane foams and other casting materials to cast a tire.
Abstract
Tire impression evidence is an important aspect of forensic investigations. In certain investigations, the tires needed for comparison may not be easily seized, removed, packaged, or shipped to the lab for comparison. In this study, three types of casting materials (Mikrosil, dental stone, and expandable foams) were examined for the casting of tires. Factors such as the level of detail provided, ease of use, durability, and cost of each material were compared. The tire used in this experiment was a new Firestone Tempa Spare. Two small rocks were placed into the tread of the tire to produce unique characteristics in the pattern. Each casting material was placed over the tire around the two inserted rocks. After the materials dried, they were removed, examined, and photographed. The comparison involved the area where the rocks had been placed. There are several considerations when determining the best material to use for casting tires. The first is the area on the tire that needs to be cast. If it is a small area, the use of Mikrosil is favored because of the quick drying time. If the area is large or a cast needs to be taken from the whole tire, expandable foam is a likely choice. Another consideration would be the durability of the cast. Polyurethane foam is extremely durable and not very flexible. Mikrosil is flexible and fairly durable compared to the foam. Dental stone can break if handled roughly. A final consideration would be the weight of the final product, especially if it has to be shipped. The results of the study showed that polyurethane foam was the logical choice for casting a tire because of the satisfactory detail, low cost, ease of use, durability, and weight of the foam. 2 references, 1 table, appendix, 10 figures