The effect of reactive dyeing of fabric on the morphology of passive bloodstains

Abstract

The majority of fabrics at crime scenes have been coloured in some way. The effect of such treatments on resultant bloodstains has not been considered. In this work, horse blood was dropped onto reactively dyed calico fabrics (100% cotton, plain woven) with three different masses of 91 g m-², 171 g m-² and 243 g m-² and the results compared to previous work on the not-coloured calico fabric. Five impact velocities were used from 1.7 ms−1 to 5.4 ms−1. The use of reactive dye increased the thickness (from 0.38 – 0.56 mm to 0.39 – 0.6 mm) and mass per unit area (from 85.1 – 224.6 g/m² to 91 – 243 g/m²) of the calico fabrics. The reactively dyed fabrics had larger bloodstains (e.g. lightest calico 41.2 – 78.6 mm²) compares to the not-coloured fabrics (e.g. lightest calico 21.4 – 67.5 mm²) across all three mass per unit areas. The dyeing of the fabrics altered the intra-yarn spaces to a more optimum size for wicking blood, increasing the ease with which the blood could wick along the yarns in the dyed calico. The amount of wicking varied depending on individual variations within the fabrics and yarns. More variation in dry bloodstain area was seen among dyed calico specimens than for the not-coloured fabric. The amount of wicking which was seen on the dyed calico meant there was no correlation between dry bloodstain area and impact velocity, a correlation which was seen on the medium and heavy not-coloured calico in the previous work.