Browsing by Author "Dicken, Lisa"

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    The effect of reactive dyeing of fabric on the morphology of passive bloodstains
    (Elsevier, 2022-04-30) Dicken, Lisa; Knock, Clare; Carr, Debra J.; Beckett, Sophie
    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.
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    The effect of the digital printing of fabric on the morphology of passive bloodstains
    (Elsevier, 2022-11-10) Dicken, Lisa; Knock, Clare; Carr, Debra J.; Beckett, Sophie
    Bloodstained fabrics found at crime scenes are likely to have had processing treatments, such as dyeing or printing, but the effect of the treatments on bloodstain morphology is not always considered. In order to study the effect of digital printing on bloodstain morphology, drip stains were created from five impact velocities (1.9–5.4 ms−1) on three different mass per unit areas (88–226 g/m²) of 100% cotton calico which had been digitally printed using reactive dye. Across all three printed fabrics, the bloodstains appeared visually similar, and no correlation was found between the dry bloodstain area and the impact velocity. When comparing the bloodstains on the printed fabric to those which had been created previously on the same fabric in a dyed and not-coloured state, the dry bloodstains on the printed fabric were statistically significantly larger (e.g. for the calico with the lightest mass per unit area, mean dry bloodstain area was 126.6, 64.4 and 44.3 mm² for the printed, dyed and not-coloured fabrics respectively). Examination of the larger bloodstains on the printed calico with the micro computed tomography scanner and scanning electron microscope, suggested that the printing process increased the wettability of the fabric, so the blood could spread more easily on the surface. This allowed the blood to coat the yarns, and wick into them before wicking along the intra-yarn spaces. The results presented in this paper showed that care must be taken when examining bloodstains at crime scenes. Depending on the fabric and the processing of the fabric the size of the blood stains may not increase with impact velocity as wicking may result in a larger bloodstain from a lower velocity. The bloodstain on the penetrated face of the fabric may be larger than on the impacted face and the same fabrics with different processing will produce different blood stain sizes and shapes.
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    Investigating bloodstain dynamics at impact on the technical rear of fabric
    (Elsevier, 2019-05-19) Dicken, Lisa; Knock, Clare; Carr, Debra J.; Beckett, Sophie
    Using high speed video, the impact of blood drops falling at three velocities (1.9, 4.2 and 5.8 ms−1) were filmed from both the technical face and for the first time the technical rear of three different mass per unit areas (85.1, 163.5 and 224.6 g/m²) of 100% cotton calico. It was seen that there were two stages in the creation of a bloodstain on fabric; the impact dynamics, followed by wicking along the intra-yarn spaces. In the first stage, once the blood impacted the fabric, blood was visible on the technical rear of the fabrics with the medium and lightest mass per unit area within as little as 0.067 ms after impact. No blood was visible on the technical rear of the fabric with the heaviest mass per unit area following impact or the medium mass per unit area from 1.7 ms−1 impacts. On the technical face of the fabric, the blood drop spread laterally and then receded for 8 ms following impact. The dynamics on the technical face were not affected by what was occurring on the technical rear of the fabric. The bloodstain on the technical rear initially only increased until 0.8 ms following impact. The increase in technical rear bloodstain area was caused by continued movement of the blood through to the rear of the fabric as the blood drop spread on the technical face. Once the impact dynamics were concluded within 8 ms of impact, there was no further change in the bloodstain for the remaining 67 ms of high speed video. Following this the blood wicked into and along the yarns, resulting in a dry technical rear bloodstain on all fabrics at all velocities.
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    Passive bloodstains on cotton fabrics
    (Cranfield University, 2019) Dicken, Lisa; Knock, Clare
    Bloodstains on finished fabrics are frequently found at crime scenes, however there has been limited work on the creation mechanisms and interaction of blood and fabric. The initial aim of this research was to verify the use of a micro computed tomography (μCT) scanner for blood pattern analysis (BPA) research. The pilot study confirmed it was possible to visualise the form of the bloodstain inside the fabric in the CT scans, providing additional information to what could be learnt from examination of the external bloodstains alone. Bloodstains were created on three mass per unit areas (85.1, 163.5 and 224.6 g/m²) of laundered 100% cotton plain woven calico from six impact velocities (1.7, 2.9, 4.1, 4.9, 5.1 and 5.4 ms-1). The bloodstains were examined with external photographs, area measurements, a μCT scanner and a scanning electron microscope (SEM). The fabric with the lightest mass per unit area (85.1 g/m²) generally produced the largest bloodstains. The blood was able to coat the yarns owing to the high porosity of the fabric and wick along the low linear density yarns. For the fabrics with the middle (163.5 g/m²) and heaviest (224.6 g/m²) mass per unit areas less wicking occurred. Dry bloodstain area increased with impact velocity due to the increase in lateral spreading at impact with greater impact velocities. The yarn linear density, sett and yarn twist altered the way in which blood interacted with the fabrics. Bloodstains were then created on the calico fabrics following reactive dyeing or digital printing. The dry bloodstain areas increased for the dyed fabric owing to the swelling of the fibres following dyeing, reducing the intra-yarn spaces to a more optimum size for wicking. The digital printing increased the wettability of the fabric, most likely with a reduction in surface roughness. This allowed the blood to spread more easily on the surface of the fabric, before wicking into and along the intra-yarn spaces. The differences seen among the dry bloodstains for the different treatments emphasise the importance of not comparing bloodstains between fabrics with different finishing treatments.
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    The use of micro computed tomography to ascertain the morphology of bloodstains on fabric
    (Elsevier, 2015-10-23) Dicken, Lisa; Knock, Clare; Beckett, Sophie; de Castro, Therese C.; Nickson, Tania; Carr, Debra J.
    Very little is known about the interactions of blood and fabric and how bloodstains on fabric are formed. Whereas the blood stain size for non-absorbent surfaces depends on impact velocity, previous work has suggested that for fabrics the blood stain size is independent of impact velocity when the drop size is kept constant. Therefore, a greater understanding of the interaction of blood and fabric is required. This paper explores the possibility of using a micro computed tomography (CT) scanner to study bloodstain size and shape throughout fabrics. Two different fabrics were used: 100% cotton rib knit and 100% cotton bull drill. Bloodstains were created by dropping blood droplets from three heights; 500 mm, 1000 mm and 1500 mm. Results from the CT scanner clearly showed the bloodstain shape throughout the fabric. The blood was found to form a diamond shaped stain, with the maximum cross-sectional area 0.3–0.5 mm below the surface. The bloodstain morphology depended on both the impact velocity and fabric structure.