Investigation of iron oxide powders for use in powder suspension formulations in fingermark development

Abstract

A powder suspension (PS) is a fine powder dispersed through a detergent and water solution. It is typically used for treating latent fingermarks on both wetted and dry adhesive, semi or nonporous surfaces. Iron oxide powder suspensions (FePS) are recommended on light non-porous surfaces and adhesive surfaces but is not commercially available. This type of PS is therefore more customisable as different iron oxide powders can be used on a range of surface types. This overall aim was to examine a variety of different iron oxide powders and investigate the impact that variations can have on fingermark development with FePS. This research was divided into two stages to understand the general performance of the iron oxide component in FePS. The first stage of this research examined the iron oxide powder in both its dry form and as a powder suspension. This stage found all iron oxide powders were more effective when applied as a suspension rather than its dry powder form. Microscopically, a clear difference between the powder selectivity of both techniques was visually observed, with the FePS technique producing more selective powder deposition than the dry powder. The optimised FePS formulation from stage 1 was then compared to the current recommended formulation in stage 2. A red iron (III) oxide PS, which has not been previously examined in literature had the best overall results in both stages and was shown to have an increased percentage of identifiable mark quality on all examined substrates, outperforming both old and new recommended FePS powders when mixed with 10 % Tween 20 surfactant. However, the recommended nano FePS was more suitable for the adhesive tape surface due to the iron (III) oxide PS having strong background development. The use of suspensions on wetted fingermarks was also examined in stage 2 and was found to not have a great impact on fingermark quality on the glass and plastic surfaces, and all formulations successfully developed fingermarks up to 1 month old. From these findings it can be stated that the type of iron oxide powder greatly influences the quality of marks that are produced with FePS. Hence, different iron oxide powders for PS do require a closer examination under the new surfactant formulation recommended.