Evaluation of 3D and 2D chronomorphometrics for latent fingermark aging studies

Latent fingermark age determination is a relatively new subdiscipline of friction ridge pattern analysis that has the potential to ascertain two key pieces of information: the "who" and the "when" from a single evidence item. In this proof-of-concept study, the sensitivity and suitability of a series of 3D and 2D chronomorphometrics, ie, quantitative measurement of form as a function of time, are examined under various temperatures (55, 21, 4, and -20°C) at 6 months. 3D imaging with an optical profiler (OP) in tandem with a conventional 2D fingermark enhancing method, ie powdering with titanium dioxide, is the technique selected. From a chronomorphometric perspective, the 3D-OP detects micrometer variations in surface texture with regard to the heights (Sa and Ra) and volume (Vu) of the ridges, whereas 2D imaging provides information on color contrast (MI and IA), the fingermark visual quality score (QS), and the relative area extension of color-coded maps of ridge clarity (BlueGreen, BG). Statistical analyses have revealed different degrees of sensitivity of the 2D and 3D metrics for detecting the effect of temperature and time, being 3D the most discriminating. In these tested conditions, warmer temperatures (55 and 21°C) have shown the most impact on ridge degradation with the lowest levels observed at -20°C. The concurrent application of 2D and 3D metrics would be considered the best approach to advance the knowledge on fingermark aging processes and possible mathematical models.