Prior research has determined that dipping tape into liquid nitrogen for separation does not interfere with the subsequent development of fingerprints on the adhesive side of duct tape. Twenty types of tape were dipped into liquid nitrogen to facilitate the separation of tape when two adhesive sides of the tape were adhered together or when the tape was adhered to a non-adhesive surface. Twelve of the twenty tapes tested were duct tapes [20].
However, it is not feasible to use the dipping method to separate duct tape on large packages or on decedents that are bound with duct tape.
The separation of adhesive materials using Un-Du has been reported in the literature. Six different types of tape, a label, and self-adhesive stamp were separated with Un-Du and the adhesive surface was processed with methanol based gentian violet, sticky- side powder and Wetwop for fingerprints. In the control sample of this experiment, where Un-Du was not used, the fingerprint ridge detail was reported on the adhesive surface of the duct tape in five trials after being processed with gentian violet, sticky-side powder and Wetwop. However, when Un-Du was used to neutralize the adhesive, the quality of the fingerprints reported for the duct tape samples tested in five trials using gentian violet, sticky-side powder and Wetwop were reported as poor. These fingerprints were described as having no definable ridge detail [24].
The exact mechanism by which suspension powder adheres to finger impressions is not completely understood. One study using a scanning electron microscope (SEM) suggested that powder suspensions form aggregations of particles which visualize the fingerprint [35].
In this experiment, microscopic examination of the tape did not offer any evidence of the mechanism for suspension powder adhering to the non-adhesive side of the tape. However, on the adhesive side of the tape, the suspension powder appears to penetrate the indentions made by papillary ridges into the tape’s adhesive. The finger ridges are not observable before processing with the suspension powder; however, the fingerprint left in the tape’s adhesive may be similar to a fingerprint that has been left in a waxy substance. Another possible mechanism may be that the papillary ridges disturb the surface layer of adhesive and create different physical properties between the disturbed and undis- turbed adhesive. When suspension powder was applied with a brush and the excess suspension powder rinsed away from the surrounding area using distilled water, the print was visible.
Figs. 3–5 illustrate the quality of the fingerprint impressions evaluated and rated as a +1, +2, or +3 based on the minutiae and pattern detail. A rating of +1 was assigned to impressions with no minutiae to limited ridge minutiae. A rating of +2 was assigned to impressions with minutia and partial pattern detail and a +3 to impressions with numerous minutiae and a more complete pattern.
When gradual force at