HUMAN HEAD HAIR AS FORENSIC EVIDENCE 309 Table II. Occurrence of bleached hairs Colour group (female) 1 2 3 4 5 6 7 8 9 % population (100) 0 28 20 9 14 7 6 4 12 No. hairs bleached 0 0 0 0 0 6 1 1 0 rinsed with water and observed. Extensive hair damage is indicated by intense blue/violet colouration. Unbleached hairs do not absorb any dye under these conditions. Hair lacquer residues A technique has been developed (Crockett (29)) for the examination of lacquer residues by infrared spectroscopy. This technique enables the type of resin used to be identified and requires only 2-3 cm of hair. However, before this technique can be used some data on the use of lacquer in the population is required. Polyvinyl pyrollidone (the major constituent of many hair lacquers) is, however, the basic material for a wide range of hair cosmetic preparations other than lacquers (e.g. sets, conditioners, etc). Hair dyes Hair dyes can be broadly classified into three types: Temporary rinses. These are essentially coloured pigments which are dis- solved in water and absorbed on the surface of the hair. They contain a wide range of compounds including azo-dyes, triphenylmethane dyes and anthraquinones. Semi-permanent dyes. These are frequently nitroaromatic amines which are strongly absorbed on the surface of the hair and give a good depth of shade. Permanent or oxidation dyes. Permanent dyes are mostly based on p-phen- aminediamine. In the dyeing process the amine penetrates the hair shaft and enters the cortex, where it is oxidized with hydrogen peroxide to yield a complex polymeric product. The development of a thin-layer chromatographic system to identify these types of dyes on single fibres has been studied (Logan (30)) but found to be impractical due to great similarity between the polymerized product of different manufacturers. Where sufficient fibres are available (i.e. 50 cm) the dyes may be extracted and identified by TLC. However, a considerable

310 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS amount of information on the type of dye can be obtained from micro- scopic examination of the fibre. Dyed hairs frequently show a more uniform distribution of colour than un-dyed hairs, i.e. there are very few pigment granules visible. In natural hair there may be a gradual decrease in pigment from base to tip, but on para-dyed hair or bleached hair the decrease is normally abrupt. Hence the identification of dyed hair does not normally present any real problem in forensic examinations. Of 200 hairs examined only 1 individual displayed dyed hair (group 6, female). If the hair displays a root then an estimate of the time since dyeing can be made, as hair is known to grow at a rate of approximately 1 cm/month. Attempts to classify hair dyes from single fibres by TLC have been studied but were shown to be impractical because of the small quantities of dye used and the difficulties of extracting the dyes without modifying them chemically. Hair rinses contain dyes in solution which deposit a relatively uneven film of the dye on the surface of the hair fibre. (Some of these rinses are based on methylene blue and methyl violet.) Observation of an individual's hair has shown that many of these rinses persist for up to 6 days but at this time the dye is very uneven and difficult to detect. Even after 1 day a significant proportion of the hair dye has been removed by brushing and combing and is completely removed by washing. Identification of medicated shampoos. One of the major limitations of the examination of cosmetic material in or on hair is the ease with which these materials can be removed by combing, brushing and washing. Phenols are known to be strongly absorbed (Breuer (31)) at polar sites in the hair keratin and are not readily removed. It was for this reason that attention was focused on formulations which contain phenols. An examination of the formulations of many medicated shampoos indicates that many of them are based upon a wide range of phenolic compounds or quaternary ammonium salts. It was not found possible, using known analytical reactions, to detect quaternary ammonium salts on hair fibres. However, examination of the common methods for identifying phenols produced a method based upon the formation of brightly coloured indophenols. The use of nitrous acid in concentrated sulphuric acid produced a reagent which partially destroyed the cuticle of the hair and allowed the reagent to penetrate the hair fibre. When a hair which had been washed using a medicated shampoo based on phenols was treated with nitrous acid an intense brown colouration was pro- duced in the body of the fibre. Hairs darker than group 6 were prebleached for 30 min using a commer- cial hair bleach. The advantage of commercial bleach over ammoniacal