Problems of Forensic Sciences 2001 Vol. 46 (XLVI) 198-202
THE EVIDENTIAL VALUE OF BLACK COTTON FIBRES
Michael GRIEVE
Forensic Science Institute, Bundeskriminalamt, Wiesbaden, Germany
Streszczenie
The comparison of wool and cotton fibres relies heavily on the comparison of the colourant. A big disadvantage is that it is not possible to identify the dye from the amount present on a single fibre. Despite this the forensic scientist is faced with the problem of estimating the frequency of fibres recovered in casework, in relation to those in the general population. One way that this can be done by considering the degree of spectral variation that occurs within a “block of colour”. When a spectral type occurs with a high frequency, the evidential value of the fibres may be so low, that it is not worth considering them as target fibres. Using uv-visible range microspectrophotometry (MSP) spectra were recorded from 73 known black cotton dyes and 158 samples of black cotton taken from various textiles. It is possible to recognise spectra originating from sulphur and with very few exceptions from reactive dyes. Direct and Vat dyes present more difficulty. The degree of spectral variation and consequent discriminating power of MSP was investigated within the various dye classes. A high degree of individuality was observed in the spectra from black reactive dyes giving a discriminating power (D.P.) of 0.91 in contrast to Sulphur dyes where the D.P. was only 0.18. Within the few direct dyes (10%) that were encountered one basic spectral form predominated, but a large number of minor variations to this were also seen.
Słowa kluczowe
Fibres; Cotton; Black dyes; Spectra; Frequency.