Quantitative colour analysis of beach and dune sediments for forensic applications: A Portuguese example

In this study, the colour of 23 sediment samples collected in different Portuguese beaches in the North (Entre-Douro and Minho) and 33 in the South (Algarve) was tested. Spectral colour parameters (L*a*b*) were measured after several presentation/pre-treatment methods: drying at 40 °C, sieving (<150 and <63 μm) and ashing at 850 °C, using a Konica Minolta CM-2600d spectrophotometer. A descriptive statistical analysis with L*a*b* values for each presentation/pre-treatment method was performed to ascertain within-sample reproducibility followed by a hierarchical cluster analysis to obtain significant discrimination between samples using colour analysis. The samples analysed presented a colour closest to red and yellow continuums and a lightness close to the pale side of the L*a*b* system colour sphere with samples collected in the North presenting analysis on average darker L values than the samples collected in the South. The cluster analysis, dried, unsieved bulk samples L*a*b* values gave the best discrimination between samples. The clusters analysis dried, unsieved bulk samples–dried, sieved <150 μm fraction set allowed better discrimination between samples compared with the dried, sieved <63 μm fraction set or dried, unsieved bulk samples–ashed bulk, unsieved samples set and even with dried, unsieved bulk samples/dried, sieved <150 μm fraction/dried, sieved <63 μm fraction/ashed bulk, unsieved samples considered all together.