TRANSFER AND PERSISTENCE OF FIBRES

• Jurisdiction: Australia

Transfer - fibres............................................................................................. [88C.500]

Persistence - fibres ...................................................................................... [88C.540]

[88C.500] Transfer - fibres

Transfer

The basis of fibre examination lies in the fact that fibres are transferred and that they can be subsequently recovered. This is based on the Locard Exchange Principle.

Named after Edmond Locard, Founder and Director of the Institute of Criminalistics at the University of Lyon, the theory, simply stated, is that every contact leaves a trace. However, it does not follow, when a transfer has taken place, that it can always be detected. In some cases, the amount of material transferred may be so small that it is not detectable or identifiable by current technology. Also, the rate of loss of some materials after transfer may be so great that the transfer cannot be detected at a very short time after transfer. For example, fibres from footwear are usually lost in a matter of minutes. Hence, the inability to locate trace materials does not of itself prove contact did not occur. The absence of evidence is not evidence of absence!

Fibre transfer studies

For fibres, comprehensive experimental validation of the theory of transfer first became available in 1975 when studies were reported from a group working at the then Home Office Central Research Establishment (HOCRE) at Aldermaston, England. Key papers and conclusions reached are presented below.

Pounds and Smalldon (1975a; 1975b; 1975c), using wool and acrylic garments, showed that the number of fibres transferred depended on a number of factors, including:

• the area of the surfaces in contact;
• the number of contacts, although here repeated contacts over the same area were found to cause transfer of some fibres back to the garment of origin;
• the force or pressure of contact, with more fibres being transferred with increasing pressure;
• the nature of the recipient garment: a cotton laboratory coat with a smooth surface proved to be a poor recipient (the coarseness of the recipient garment seems to be important); and
• as high pressure and coarse recipient garments produced a greater proportion of short fibres than did low pressure and smooth recipient garments, it was suggested by the authors that fragmentation of fibres during contact may be an important mechanism in fibre transference.

Kidd and Robertson (1982) carried out similar experiments but used a wider variety of fibre types as both donor and recipient garments. Their findings were in broad agreement with those of Pounds and Smalldon (1975a) while emphasising the importance of:

• the nature of both the donor and the recipient garments with respect to both fibre composition and texture of the fabric;
• force or pressure of contact - the number of fibres transferred increased with increasing pressure up to a point beyond which increasing pressure led to no further increase;
• fibre type - far fewer polyester and viscose fibres were transferred than were cotton, acrylic or wool fibres where the donor fabric was composed of fabrics comprising these fibre types;
• differential transfer - the proportion of polyester and viscose fibres transferred from a mixed fabric was close to the ratio of these fibres in the donor fabric;
• fibre length - most (over 80%) of the polyester or viscose fibres transferred were under 5mm in length.

Transfer in blended fabrics

Further work by Parybyk and Lokan (1986) and by Salter, Cook and Jackson (1984) has shown that in some blended fabrics, the number of fibres transferred of the different types is not proportional to the stated fibre composition of the garment. For example, Salter, Cook and Jackson (1984) showed that with 65:35 polyesterxotton, 55:45 polyestenwool and 70:30 polyestenviscose donor fabrics, in each case most fibres were shed from the minor component. In some experiments with the polyester-wool mix, only wool fibres were transferred. Parybyk and Lokan (1986) found that the shedding ratio...