R.J. Dudley

The use of colour in the discrimination between soils.

The use of Munsell Soil Colour Charts is suggested for routine measurement and local data collection of dry soil colours. This enables a weighting to be given to the evidential value of a colour match between suspect and control samples in the relevant area. Procedures are described for recording moist and ashed soil colours and these are evaluated for their discrimination between soils having the same dry colour. Ashing is found to have a very good discriminatory potential and is suggested as a routine procedure. Moistening, however, does not have such a good discriminatory potential, but is a simple technique that may be useful for small samples when ashing is not indicated because of its destructive effect.

The Particle Size Analysis of Soils and its Use in Forensic Science—The Determination of Particle Size Distributions Within the Silt and Sand Fractions

Methods are described for the determination of the particle size distributions in small soil samples using a Coulter Counter Model ZB for the silt fraction (60μm–2μm) and conventional sieving for the sand fraction (2mm–60μm). An examination of the reproducibility of the methods using duplicate 1·5g samples of eighteen different soils has shown that they are highly reproducible and that the differences between the soils were easily demonstrated both in the silt and sand particle distributions. The methods have also been shown to be reproducible for sample weights as low as 200mg of whole soil.

THE DISCRIMINATION OF SMALL FRAGMENTS OF HOUSEHOLD GLOSS PAINT BY MICROSPECTROPHOTOMETRY

A microspectrophotometer has been used to discriminate between sets of household gloss paints of the same British Standard colours obtained from different manufacturers. Reflectance spectra were obtained, over the range 390 to 900 nm, from paint top surfaces and individual cross-sectional layers. Comparison of the reflectance spectra enabled visually similar paints to be discriminated.

A Summary of Data Obtained from a Collection of Fibres from Casework Materials

Data recorded for representative fibre samples from control items examined by fibre examiners in the Home Office Forensic Science Laboratories and Metropolitan Police Forensic Science Laboratory are reported. Two collections lasting two months each {in winter and summer) were examined. In all, 3,836 items were examined yielding 10,034 different fibre records. The distributions in item type, fibre type and colour are discussed.

The Extraction and Classification of Dyes from Cellulose Acetate Fibres

A simple scheme is described for the extraction and classification of dyestuffs from 1cm to 2cm lengths of sec-cellulose acetate and cellulose triacetate fibres.

A Simple Method for Determining the pH of Small Soil Samples and its use in Forensic Science

The value of pH measurement as a discriminatory technique for soils is investigated with particular reference to the development of a technique for the examination of very small samples. The variation of pH within five groups of soils of widely varying dry colours has been determined and found to be quite considerable, the distribution within each group being very similar. The discriminating power for the technique has been estimated to be approximately 0·4. Four colorimetric methods, based on BDH Soil Indicator, have been evaluated for their possible use in forensic science. A method in which a water to soil ratio of 2·5:1 v/w and a centrifuge for settling purposes were used was found to be the most satisfactory and capable of yielding reproducible pH values for samples varying from 2·5g to 50mg. A study of the effects of storage of a moist soil in a sealed polythene bag indicated no change in pH for up to fourteen days of storage.

The non-destructive analysis of single layered household paints using energy dispersive x-ray fluorescence spectrometry.

An evaluation of energy dispersive X-ray fluorescence spectrometry for the discrimination of single layered household paint flakes of similar colour is reported. Thirty paint samples, ten from each of the three colour groups red, green and white, were analysed under standard conditions. The reproducibility of the X-ray fluorescence spectra, for 2mm × 2mm flakes removed from different areas of a painted slide, has been investigated. Using 2mm × 2mm flakes discrimination of all the paints within the red and green colour groups was achieved. The white paint flakes were discriminated into nine groups. A combination of several other techniques could not achieve discrimination of all the samples. The spectra for all the paints examined are shown and the limitations of the method are discussed.

The Discrimination of Modern Household Paints Using Thin Layer Chromatography

Abstract Extraction of coloured household gloss paint fragments with dichloromethane, and TLC of the extracted material on silica gel plates with a mixture of chlorobenzene, toluene and 1,2-dichloroethane (1:1:1 v/v), provides good discrimination between visually similar red, orange, yellow, dark blue, purple and brown paints, and fairly good discrimination between green paints. The discrimination available between visually similar blue-green and light blue paints, however, is low. The additional step of re-extracting the paint fragments with 1,2-dichlorobenzene and TLC of the extract with a mixture of 1,2-dichlorobenzene, toluene and 1,2-dichloroethane (2:1:1 v/v) improves the discriminating power for green, blue-green, dark blue, purple and brown paints. TLC provides a simple but powerful method of characterising household gloss paints on the basis of the organic pigments present in the paint film and should complement other techniques.