Andrew W. Hartshorne

Colour measurements on single textile fibres

Abstract The microspectrophotometer is used primarily to discriminate between visually identical fibres on the basis of their visible absorption spectra. However, these spectra can also be used to generate codings to describe the colours of single fibres. This coding is a prerequisite for the collection of data about fibres, colour being the most important feature for distinguishing between fibres of the same generic type. The colours of some polyester, wool and cotton fibres have been measured and the associated errors in coding evaluated. An important feature of the system used is that it allows for the variation in dye uptake from fibre to fibre which is present in typical casework samples.

A Fiber Data Collection for Forensic Scientists—Collection and Examination Methods

Methods used in U.K. forensic science laboratories to establish a large fiber data base are described including details of the recording of fiber sources, types, and colors. Such a data base provides a firm foundation for the assessment of the significance of fiber matches encountered in casework.

THE EXTRACTION AND CLASSIFICATION OF DYES FROM COTTON AND VISCOSE FIBRES

Abstract A simple sequential scheme is described for the extraction and classification of dyestuffs from 10–20 mm lengths of single cotton or viscose fibres.

THE DEFINITION OF COLOUR FOR SINGLE TEXTILE FIBRES BY MICROSPECTROPHOTOMETRY

Abstract Previous work showed that replicate determinations of complementary chromaticity coordinates from different fibres within a sample fell within elliptical error regions. The ellipses were aligned towards the yellow portion of the chromaticity diagram. In addition, samples dyed with different concentrations of the same dye produced complementary chromaticity coordinates which fell along lines passing through the same yellow region. These effects are now shown to be due to the influence of the undyed fibre substrate on the overall fibre colour. Instrumental error, delustrant level and fibre shape have also been investigated as factors causing variation in complementary chromaticity coordinates.

The dye classification and discrimination of coloured polypropylene fibres

Abstract A sequential extraction and classification scheme for dyed polypropylene fibres is presented together with suitable thin-layer chromatography (TLC) systems for separating the extracted dyes. Pigment coloured polypropylene fibres are unaffected by solvents and are therefore characterised by microspectrophotometry.

The identification of polyolefin fibres by infrared spectroscopy and melting point determination

Abstract The use of infrared spectroscopy and melting points is investigated for the discrimination of polyolefin fibre types and mixtures. Polypropylenes can be characterised by infrared spectroscopy while the identification of polyethylene types and mixtures requires the additional determination of their melting points.

The standardisation of thin layer chromatographic systems for comparison of fibre dyes

Commercially available TLC development systems were compared on the basis of convenience, reproducibility and resolution. Chromatograms produced using both the Camag No 25155 tank and the Kodak No 13260 tank were reproducible, but the former system was more convenient to use. A series of standard dye mixtures, covering acid, basic, direct, disperse and reactive dyes, was prepared so that TLC systems might be assessed for performance.

Thin layer chromatography of azoic dyes extracted from cotton fibres

A thin layer chromatography system has been produced for the examination of azoic dyes extracted from single cotton fibres. Dyes of this class are successfully analysed by using ethyl acetate for initial sharpening of dye spots followed by separation in a mixture of chlorobenzene, 1,2-dichloroethane and acetone (20: 20: 1).

Color Matching Within a Fiber Data Collection

The fiber data collection in use in the Home Office Forensic Science Service uses complementary chromaticity coordinates as a method of color description. Color variation within samples is represented by an elliptical error region around the mean chromaticity point of the sample. For searching this collection, a method of matching single colors to the collection ellipses has been assessed. However, the necessary calculations are complex, so a number of simpler alternatives has been investigated. A simple box search has been found to be convenient, albeit with some reduction in specificity.

The discrimination of cellulose di- and tri-acetate fibres by solvent tests and melting point determination

Current methods of identification for di- and tri-acetate fibres based on solvent testing do not always give a clear and unambiguous result. Alternative solvents are presented, which provide an improved level of performance. Melting point determination is also shown to be applicable to the identification of the two types of acetate fibre.