The Effects of Polymer Pigmentation on Fingermark Development Techniques

Abstract

Latent fingerprint deposition and effectiveness of detection are strongly affected by the surface on which prints are deposited. Material properties, surface roughness, morphology, chemistry and hydrophobicity can affect the usefulness or efficacy of forensic print development techniques. Established protocols outline appropriate techniques and sequences of processes for broad categories of operational surfaces. This work uses atomic force microscopy and scanning electron microscopy to investigate a series of surfaces classified as smooth, non-porous plastic. Latent prints developed with iron oxide powder suspension are analysed on a range of scales from macro to nano to help elucidate the interaction mechanisms between the latent fingerprint, development agent and underlying surface. Differences between surfaces have a strong effect, even within this single category. We show that both average roughness and topographical feature shape, characterized by skew, kurtosis and lay, are important factors to consider for the processing of latent fingerprints.

Fingermark visualisation with iron oxide powder suspension: The variable effectiveness of iron (II/III) oxide powders, and Tween® 20 as an alternative to Triton™ X-100

“…Surface cleanliness was also an influencing factor, since some powder suspensions caused greater staining on sample areas that had not been cleaned. Earlier works demonstrated the importance of the substrate properties in fingermark visualisation [10,13], and Experiment 1 further highlights this, as the intensity of background staining caused by 1% surf sol (B) powder suspension also varied between materials ( Figure 2).…”

“…Effective powder suspension formulations should selectively deposit powder on fingermark ridges and not the backgrounds of the surfaces to which they are applied. General 'background staining', caused by surface-wide powder deposition, is undesirable as it may reduce the contrast of visualised fingermark ridges [13,14] and render fainter marks difficult to observe. Recently, the 'fingermark selectivity' exhibited by the C-IOPS-09 formulation was shown to relate to the concentration of the surfactant Triton™ X-100 [7].…”

“…It should be noted that additional processes can cause background staining effects to occur when powder suspensions are applied to incompatible surfaces. Known examples include C-IOPS-09 on acrylic-based adhesives such as some parcel tapes [2,16] and carbon-based powder suspension on surfaces containing titanium dioxide, a common pigment in light coloured polymers [13].…”

“…This experiment utilized a 'spot-testing' methodology: a pair of marked areas (30 x 60 mm) on each substrate (1-7, as per Table 1) was treated with each powder suspension: this size has been shown to be sufficient for analysis of substrate variation [13]. One marked area from each pair had been pre-cleaned on the day of the experiment, whilst the other had not been cleaned.…”

“…cases may contribute to the background staining, the degree of which is likely to be substrate and surfactant dependent [10,13].…”