J. Forens. Sci. Soc. (1975), 15, 17
The Transfer of Fibres Between Clothing Materials During- Simulated Contacts and their Persistence During Wear Part I-Fibre
Transference
C. A. POUNDS and K. W. SMALLDON Home O@ce Central Research Establishment, Aldermaston, Reading, Berks, R G 7 4PN, England The number of wool and acrylic fibres transferred to various articles of clothing during simulated contacts has been studied. The variation of the number of jibres transferred from a new wool sweater with area of contact is described and repeated contacts over the same area were found to cause the transfer of somejibres back to the garment of origin. The effects of pressure, type of recipient garment, number of repeated contact passes and jibre length were investigated for wool Jibres using a balanced four-way classijication experiment. After the anaGysis of variance all four e - t s , the pressure-length interaction and the garment-length interaction were found to be signijicant. The number of jibres transferred increased considerably with pressure and despite their surface appearance morejibres were observed on the recipientjackets than on the sweaters. When the same area of material was used for repeated contact passes the number of jibres transferred at each pass progressively decreased. The transference of jibres from the new wool sweater was compared to that from an old sweater and a square of handknitted acrylic material in a three-way classijication experiment. The signijicance of recipient garment and the number of contact passes was confirmed but no signijicant dzference was found i n the number of fibres produced by the three dzferent transferring materials. A s high pressure and coarse recipient garments produced a greater proportion of short jibres than low pressure and smooth recipient garments, it is suggested that fragmentation ofjibres during the contact may be an important mechanism i n jibre transference. Introduction Fibre transference from the outer clothing of the assailant to the victim and vice versa is of particular interest in the investigation of many crimes, including assaults and sexual offences, where violent bodily contacts are known to have occurred. Fibres are also of interest in other crimes, such as breaking offences, where they are often found adhering to freshly splintered woodwork or other objects at the scene of crime. However, in these circumstances the examination of fibres and interpretation of results is relatively straightforward compared with the problem involved in establishing whether or not a contact has occurred between two sets of clothing. Although fibre examinations have been conducted for many years in cases involving clothing contacts no experiments have been reported concerning either the number of fibres which are likely to be transferred in various contact situations or the number which are likely to persist after various periods of wear. The later point being particularly important since there is frequently a delay of several days before a suspect is apprehended. In the past, the transfer of fibres between items of clothing has been explained using the ideas of contact transfer first postulated by Locard (1928, 1930) which were later discussed by Tryhorn (1935) and Kirk (1949, 1953) and which eventually became known as Locards Exchange Principle (Nickolls, 1956). However, no experimental validation of this principle has been reported for most types of evidence including fibres. Although it seems likely that some fibres
would be transferred in most contact situations it would be a n advantage if the exchange principle could be investigated on a t least a semi-quantitative experimental basis so that the numbers of fibres transferred and how many persist during wear could be estimated. As there is an absence of basic information concerning fibre transference and persistence, the forensic scientists will have difficulties in both the planning of fibre searches on clothing and in the interpretation of the results obtained. Even if the number of fibres which were likely to remain on clothing could only be predicted crudely then the search could be designed accordingly. A more difficult situation arises when a search for fibres is made but none are recovered. The forensic scientist is then faced with the problem of whether this indicates that the garment was not the one which was in contact a t the crime scene, or whether in fact it could be the garment but only a small number of fibres were transferred and these have all been lost during subsequent wear. I n this paper the factors which affect the transference of fibres during clothing contacts have been investigated. The most difficult problem involved in these experiments was the retrieval and counting of fibres after transference which would be both difficult and laborious using the searching techniques currently employed in forensic science (Frei-Sultzer, 1951). These difficulties were overcome by labelling the fibres with brightly fluorescent dyes so that they could be readily observed and counted under ultraviolet light. I t must be appreciated that the total number of variables which could be examined for fibre transference are numerous and therefore it was necessary that the variables should be deliberately but selectively restricted. The results from a recent survey for forensic science laboratories in England, which were analysed by the authors, showed that 60% of the garments examined in fibre cases contained wool or acrylic fibres and therefore these two types were selected as the transferring materials. An effort was also made to select a representative range of recipient clothing to which the labelled fibres would be transferred. The six items chosen were three woollen jackets of varying surface appearance, one acrylic and one wool/nylon sweater and one cotton laboratory coat. Although these were all items of men's clothing there is no reason to believe that materials with similar characteristics are not worn by women. This paper describes the number and size distribution of fibres which were transferred from wool and acrylic materials to different recipient garments for various areas of contact, different pressures and for consecutive contact passes.
Experimental Textile Materials used for Transference The two woollen sweaters and one handknitted square of acrylic material which were used for transference are described in Table 1. One of the sweaters had been extensively worn and the other was new, having been purchased for the experiments from a large chain store. TABLE 1 A DESCRIPTION OF THE TEXTILE MATERIALS USED FOR FIBRE TRANSFERENCE
Source of Material Marks and Spencers sweater Hornes sweater
Paton's 101 Courtelle
Identification Mark Description Fluorescent Labelling t~ A natural Shetland Fluorescein Wool sweater purchased for the experiments t2 A pale brown fine Fluorescein wool sweater which had been extensively worn t3 A red square which Dye in fibre already had recently been shows an intense hand knitted red fluorescence
Fluorescent Labelling The woollen sweaters were labelled with fluorescent dye by immersion in a concentrated solution of sodium fluorescein at 50°C for 30 minutes, they were then washed in running water to remove excess dye and air dried. The acrylic knitting material was red in colour and the dyestuffs present already showed an intense red fluorescence. Recipient Garments The six recipient garments used in the transfer experiments are described in Table 2. The garments were of different manufacture, composition and surface appearance. Some were purchased for the experiments while others had already been worn for a considerable period. TABLE 2
A DESCRIPTION O F T H E SIX RECIPIENT GARMENTS T O WHICH FIBRES WERE TRANSFERRED Recipient Garment Jacket
Manufacturer Daks
Fibre Type Wool
Sweater
Handknitted
Wool/nylon
rz
A bulky green sweater which had been worn for 1 year
Sweater
Harry Fenton
Courtelle Acrylic
r3
A fine yellow sweater which had been worn for 2 years
Jacket
Hepworths
Wool
r4
A typical jacket from a two-tone blue suit which had been worn for 1 year
Jacket
Guards
Wool
r5
A fine brown-checked sports coat which was purchased new for experiments
Cotton
r~
A normal white laboratory coat which had been worn for 2 years
Laboratory Coat Johnson and Sons
Identification Mark Description rl A multi-coloured check tweed jacket purchased new for experiments
Standard Method of Contact Unless otherwise stated the transferring materials were pinned to a 14cm x 14cm expanded polystyrene block and this was pressed by hand against the recipient garment which was placed on a laboratory bench. The block was then pulled across the recipient garment for a distance of 30cm a t a constant pressure. Pressure Two levels of pressure were applied by hand during the various contacts. The low pressure was approximately 30kg/m2and the high pressure approximately 300kg/m2. Repeated Contact Passes During the experiments the selected area of the transferring material was repeatedly pulled across the recipient garments for up to eight consecutive contact passes. The fibres were removed manually or by gentle application of adhesive tape between each contact pass. Fibre Length The approximate length of each transferred fibre was recorded in one of the following size ranges: 0.5-2mm, 2-5mm, 5-10mm and greater than 1Omm.
Recording of Results The recipient garments were examined under a lamp fitted with two 4ft long Phillips T L 4 0 ~ 1 0 8ultraviolet tubes which enabled fibres of more than 0.5mm in length to be counted and recorded. Identification of Factors The various factors in the experiments were identified as follows: T=the effect of transferring material. (The three transferring materials used were identified as t,, t, and t, and are described in Table 1.) R=the effect of recipient garment. (The six recipient garments were identified as r,, r 2 . . . r, and are described in Table 2.) P=the effect of pressure. (The low pressure (30kg/m2)was identified as p, and the high pressure (300kg/ my-. as p,.) C=the effect of repeated contact passes. (The first contact pass was identified as c, and subsequent passes as c,, c, . . . c,.) L=the effect of fibre length. (The smallest size classification was identified as 1, and the larger ones as l 2 . . . 14.) First order interactions were identified from the appropriate effects, e.g. the interaction between pressure and recipient garment was identified as PR. 1
\
Preliminary Investigation Reverse Transference The possibility was investigated that under the conditions used, fibres which were transferred on earlier contact passes could return to the transferring material during subsequent passes. Fibres were transferred from wool sweater t,, using the standard contact procedure and high pressure p,, to the surface of recipient garments r,-r,. After the number of fibres had been recorded a n exactly similar but non-fluorescent sweater was pulled over the same area using similar conditions. The number of fibres which were transferred back to the sweater was then determined. The percentage of fibres which showed this reverse transference from the various recipient garments are shown in Table 3. During the subsequent experiments the fibres were removed after each contact pass thus eliminating this effect. TABLE 3 THE PROPORTION O F FIBRES FROM THE FIRST CONTACT PASS WHICH WERE REVERSE TRANSFERRED DURING THE SECOND PASS FOR DIFFERENT RECIPIENT GARMENTS Recipient Garment
Proportion of Fibres Reverse Transferred (%) 37 41 44 44 60
Area of Contact The number of fibres transferred to garment r, from the wool sweater t, was determined at high pressure p, for square contact areas of 30cm2, 110cm2and 202cm2. The standard contact conditions were used and the results obtained are shown graphically in Figure 1. I t would be reasonable to expect that the number of fibres transferred would be proportional to the area of contact but the number transferred increased
more slowly than this in practice (Figure 1). There are probably two causes for this behaviour. One is that the extent of reverse transference increases with the area of contact and the other is that it is more difficult to ensure complete contact over large areas of two garments than over small areas. On the basis of these results a contact area 14cm x 14cm was chosen for future experiments.
0
r
I
AREA
a
100 OF CONTACT
I
h
200
ctv12
Figure 1. Number of fibres transferred from wool sweater t, to jacket r, at pressure p, plotted against area of contact.
Investigation of Important Factors in Wool Transference The effect of pressure, recipient garment, fibre size and repeated contact passes and their first order interactions were investigated for wool fibres using a balanced four-way classification experiment (Kendall and Stuart, 1966). The variables examined were, two levels of pressure, six recipient garments, eight repeated contact passes and four levels of fibre length making a total of 384 treatment combinations. The new woollen sweater t, was used throughout as the transferring material in this experiment because twelve identical areas of 14cm x 14cm were required and only this garment was sufficiently homogeneous. The outer surface of the transferring garment t1 was divided into twelve identical areas and each area was allocated to a pressure/garment combination. The experiment was deliberately arranged so that the high and low pressure contacts on the same recipient garment were always performed using outer areas of the transferring sweater tl but on different sides, and at different relative locations. The eight contact passes were conducted in the standard manner and the fibres were counted and removed before the next contact pass.
The total number of fibres observed for the ninety-six treatment combinations of pressure recipient garment and contact pass number is shown in Table 4 and the size distribution of the fibres is shown in Table 5 . TABLE 4 THE NUMBER OF FIBRES TRANSFERRED FROM MATERIAL t. FOR NINETY-SIX TREATMENT COMBINATIONS OF PRESSURE, R E ~ I P I E N T GARMENT AND REPEATED CONTACT PASSES Pressure
Recipient Garment
Contact Pass Number c,
c2
c,
re
70 1 290
41 1 213
27 4 121
ro
6 1 2 548 443
c4
c,
c,
c,
c,
Total
18 3 59
13 5 77
236 37 1052
2 1 4 314 342
61 3201
A.
ra
Total
Total
1
5 393
20 2
98
25 4
3 421
102
7 373
22 4
92
2 367
4
TABLE 5 THE SIZE DISTRIBUTION OF TRANSFERRED WOOL FIBRES FOR TWO DIFFERENT PRESSURES AND SIX RECIPIENT GARMENTS (percentages in brackets) Premre
Recipient Garment
11
Fibre Length 1z 1s
14
Treatment of Results The effects and first order interactions were investigated by a n analysis of variance as described by Kendall and Stuart (1966). The laboratory coat r, was excluded from this statistical analysis since the number of fibres transferred to it was always small and the results for this garment were obviously not typical simply by inspection. No replication was possible because the properties of the transferring sweater changed with the number of contact passes, and therefore the residual from the third order interaction was used to test the significance of each effect and first order interaction by means of the F distribution tables which were entered with the appropriate degrees of freedom. The results of the analysis of variance, excluding the laboratory coat r, are shown in Table 6.
TABLE 6 ANALYSIS O F VARIANCE FOR THE EFFECTS O F PRESSURE (P), RECIPIENT GARMENT (R), REPEATED CONTACT PASSES (C), FIBRE SIZE (L) AND THEIR FIRST ORDER INTERACTIONS
Source of Vaiiatwn P R C L PR PC PL RC
Degrees of Freedom 1 4
CL Residual
21 229
Sum of Squares 14,218 1,602 3.72 1
7
Mean Square 14,218 40 1 532
Significancne Level
*** *** ***
3 4
7 3 28
=99%;
NS=not significant at 5% level.
Discussion Table 6 shows that the effects of pressure P, recipient garment R, contact pass number C, fibre length L and the interaction between pressure-fibre length PL and recipient garment-fibre length RL are all highly significant. The number of fibres transferred increased with pressure, the grand total of fibres transferred at the higher pressure p, being about three times that at the lower pressure p, as shown in Table 4.
FIBRE LENGTH M M
P2 Figure 2.
PI
Comparison of size distribution of fibres transferred to jacket r, at pressures p, and p,. 23
A significantly larger number of fibres were observed on some recipient garments than on others. Table 4 shows that at both high and low pressures the largest number of fibres was found on recipient garment r, followed by r,, r,, r3, r 2 and r,. The number of fibres transferred decreased as the contact pass number increased and as can be seen from the column totals in Table 4 the number of fibres transferred in the eighth pass c, was about half that for the first pass c,. The effect of fibre length L is significant but this simply reflects the fact that all the categories of fibre size are not equally populated. The interaction between pressure and fibre length PL can be interpreted with reference to Table 5 since the proportion of fibres which are larger than lOmm is greater a t low pressure than at high pressure. This is demonstrated graphically in Figure 2 for recipient garment r,. The highly significant interaction between recipient garment and fibre length R L can be interpreted with reference to Table 5 since the size distribution of fibres is seen to vary from one recipient garment to another. This interaction is demonstrated graphically in Figure 3 by comparing the size distribution of fibres found on jacket r, with that for the laboratory coat r,. Predominantly short fibres were found on the jacket whereas most fibres on the laboratory coat were much larger. The laboratory coat r, was not included in the overall statistical analysis but Tables 4 and 5 show that this garment produced results which were quite different from the other 5 recipient garments. The number of fibres transferred to the laboratory coat was always low and increased only moderately with pressure (Table 4). The majority of fibres observed on this garment were longer than 5mm (Figure 3) and the number transferred varied erratically with the contact pass number (Table 4). A Comparison of Transferring Materials A further experiment was conducted in order to determine if the results already obtained for transferring sweater t, were typical of sweaters in general. The transferring materials compared were the original woollen sweater t,, a fine woollen sweater which had been extensively worn t, and a square of recently knitted acrylic material t,. The comparison was performed using a balanced three-way classification experiment, the variables being the three transferring garments, two recipient garments (the jacket r, and the sweater r,) and two repeated contact passes, making a total of twelve treatment combinations. The contact passes were performed in the standard manner. The fibres were counted and removed before the second contact pass. The number of fibres transferred for each of the twelve treatment combinations is shown in Table 7. TABLE 7 THE NUMBER O F FIBRES TRANSFERRED AT HIGH PRESSURE (P,) FOR TWELVE TREATMENT COMBINATIONS O F TRANSFERRING MATERIAL, RECIPIENT GARMENT AND REPEATED CONTACT PASSES Recipient Garment
Transferring Garment t1
rl
=3
t, t3 Total
Contact Pass Number CI
138 169 148 455
C2
107 117 164 388
Total 245 286 312 843
tl t2 t3 Total
Treatment of Results The effects and first order interactions were investigated by an analysis of variance as described previously and the results are shown in Table 8.
TABLE 8 ANALYSIS OF VARIANCE FOR THE EFFECTS OF TRANSFERRING MATERIAL (T), RECIPIENT GARMENT (R), REPEATED CONTACT PASSES (C) AND THEIR FIRST ORDER INTERACTIONS IN FIBRE TRANSFERENCE Source of Variation T R C TR TC RC Residual
*=95%;
Degrees of Freedom
Sum of Squares
Mean Square
Significance Level
NS=not significant at 5% level.
Discussion Table 8 shows that the effects of recipient garment R and contact pass C are significant at the 5% level but the effect of transferring material and the first order interactions are not significant. In this smaller experiment the effect of recipient garment and contact pass number have been confirmed. Although there is some variation in the number of fibres observed for different transferring materials (Table 7) this variation is not significant at the 5% level and thus there is no reason to believe that the woollen sweater t, is in any way unrepresentative of sweaters in general. General Discussion The current understanding of fibre transference is based on concepts which were formulated more than forty years ago but these have not been studied experimentally. The fibres are usually thought of as being loose on the surface of the transferring garment and are therefore capable of being shed during contact. Such concepts cannot adequately explain the results obtained in this study. It seems likely that fibres are being continuously transferred from the transferring garment to the recipient garment and vice versa during each contact pass. In the main four-way classification experiment fibres were removed after each contact thus eliminating reverse transference during subsequent passes and therefore the values recorded in Table 4 probably overestimate slightly the number of fibres which would be transferred in a normal contact. The number of wool fibres transferred increased with the area of contact (Figure 1) but not in direct proportion. This effect could be due to reverse transference which occurs during each contact pass so that for large areas of contact there is a greater opportunity for transferred fibres to return to the garment of origin than for smaller areas. However, such effects are likely to be small compared with other variations such as pressure and recipient garment. The number of fibres transferred increased with pressure and decreased with consecutive contact passes. Such results are not unexpected but it is surprising that the number transferred from the three transferring materials (Table 1) varied only slightly whereas the number of fibres found varied considerably from one recipient garment to another (Table 4). As anticipated very few fibres were transferred to the smooth cotton laboratory coat and those fibres which were found showed a very different size distribution from that observed on the other recipient garments (Figure 3). This shows that the mechanism of fibre transfer for the laboratory coat is fundamentally different from the mechanism for the other garments. The interaction observed betwe& pressure and fibre length shows that a higher proportion of short fibres are found at high pressure than at low pressure and this suggests that fibres are being fragmented during each contact. If this is so it would also explain the interaction between recipient garment and fibre
length as the rough garments would be expected to cause more fragmentation, ie, more short fibres, than the smooth garments. In this event the differences observed between the laboratory coat and the other garments (Figure 3) may simply reflect the fact that very little fragmentation can occur on such a smooth garment. The mechanisms which produce fibre transference have been investigated further and the results will be reported later.
FIBRE LENGTH MM
R4
R6
Figure 3. Comparison of size distribution of fibres transferred to jacket r, and laboratory coat r, at pressure p,.
As in these experiments the conditions had to be controlled, it was necessary to use simulated rather than real life contacts. Subject to these and other limitations, the results in Table 4 should allow working estimates to be made for the number of fibres which are likely to be transferred from sweaters during their contact with other garments. In casework there is almost always a delay, sometimes of several days, between the contact at the scene of crime and a suspect being apprehended. I t is therefore not only of interest to estimate, albeit crudely, the number of fibres which would have been transferred originally but also to estimate how many of these would have been lost during subsequent wear. The persistence of wool and acrylic fibres has been determined during wear on the six recipient garments described in these experiments and the results are described in a further paper (Pounds and Smalldon, 1975).
Acknowledgements The authors wish to thank Mr. V. J. Emerson for advice and criticism during the project. We are particularly indebted to Mr. I. W. Evett, West Midlands Forensic Science Laboratory, for his assistance with the statistical analysis.
References FREI-SULTZER, M., 1951, Kriminalistik, 17/18, 190. KENDAL, M. G., and STUART, A., 1966, The Advanced Theory of Statistics, Vol. 3, p.38, Griffen, London KIRK,P. L., 1949, J.Crim.Law and Criminal., 40, 362. KIRK,P. L., 1953, Crime Investigation, p.38, Interscience, New York. LOCARD, E., 1928, Police J., 1, 177. LOCARD, E., 1930, Amer.J . of Pol.Sci., 1, 276. NICKOLLS, L. C., 1956, The Scientific Investigation of Crime, p.39, Butterworth, London. K. W., 1975, J. Forens. Sci. Sac., 15, 29. POUNDS, C. A., and SMALLDON, TRYHORN, F. G., 1935, Police J., 8, 401.
The Transfer of Fibres Between Clothing Materials During- Simulated Contacts and their Persistence During Wear Part I-Fibre
Transference
C. A. POUNDS and K. W. SMALLDON Home O@ce Central Research Establishment, Aldermaston, Reading, Berks, R G 7 4PN, England The number of wool and acrylic fibres transferred to various articles of clothing during simulated contacts has been studied. The variation of the number of jibres transferred from a new wool sweater with area of contact is described and repeated contacts over the same area were found to cause the transfer of somejibres back to the garment of origin. The effects of pressure, type of recipient garment, number of repeated contact passes and jibre length were investigated for wool Jibres using a balanced four-way classijication experiment. After the anaGysis of variance all four e - t s , the pressure-length interaction and the garment-length interaction were found to be signijicant. The number of jibres transferred increased considerably with pressure and despite their surface appearance morejibres were observed on the recipientjackets than on the sweaters. When the same area of material was used for repeated contact passes the number of jibres transferred at each pass progressively decreased. The transference of jibres from the new wool sweater was compared to that from an old sweater and a square of handknitted acrylic material in a three-way classijication experiment. The signijicance of recipient garment and the number of contact passes was confirmed but no signijicant dzference was found i n the number of fibres produced by the three dzferent transferring materials. A s high pressure and coarse recipient garments produced a greater proportion of short jibres than low pressure and smooth recipient garments, it is suggested that fragmentation ofjibres during the contact may be an important mechanism i n jibre transference. Introduction Fibre transference from the outer clothing of the assailant to the victim and vice versa is of particular interest in the investigation of many crimes, including assaults and sexual offences, where violent bodily contacts are known to have occurred. Fibres are also of interest in other crimes, such as breaking offences, where they are often found adhering to freshly splintered woodwork or other objects at the scene of crime. However, in these circumstances the examination of fibres and interpretation of results is relatively straightforward compared with the problem involved in establishing whether or not a contact has occurred between two sets of clothing. Although fibre examinations have been conducted for many years in cases involving clothing contacts no experiments have been reported concerning either the number of fibres which are likely to be transferred in various contact situations or the number which are likely to persist after various periods of wear. The later point being particularly important since there is frequently a delay of several days before a suspect is apprehended. In the past, the transfer of fibres between items of clothing has been explained using the ideas of contact transfer first postulated by Locard (1928, 1930) which were later discussed by Tryhorn (1935) and Kirk (1949, 1953) and which eventually became known as Locards Exchange Principle (Nickolls, 1956). However, no experimental validation of this principle has been reported for most types of evidence including fibres. Although it seems likely that some fibres
would be transferred in most contact situations it would be a n advantage if the exchange principle could be investigated on a t least a semi-quantitative experimental basis so that the numbers of fibres transferred and how many persist during wear could be estimated. As there is an absence of basic information concerning fibre transference and persistence, the forensic scientists will have difficulties in both the planning of fibre searches on clothing and in the interpretation of the results obtained. Even if the number of fibres which were likely to remain on clothing could only be predicted crudely then the search could be designed accordingly. A more difficult situation arises when a search for fibres is made but none are recovered. The forensic scientist is then faced with the problem of whether this indicates that the garment was not the one which was in contact a t the crime scene, or whether in fact it could be the garment but only a small number of fibres were transferred and these have all been lost during subsequent wear. I n this paper the factors which affect the transference of fibres during clothing contacts have been investigated. The most difficult problem involved in these experiments was the retrieval and counting of fibres after transference which would be both difficult and laborious using the searching techniques currently employed in forensic science (Frei-Sultzer, 1951). These difficulties were overcome by labelling the fibres with brightly fluorescent dyes so that they could be readily observed and counted under ultraviolet light. I t must be appreciated that the total number of variables which could be examined for fibre transference are numerous and therefore it was necessary that the variables should be deliberately but selectively restricted. The results from a recent survey for forensic science laboratories in England, which were analysed by the authors, showed that 60% of the garments examined in fibre cases contained wool or acrylic fibres and therefore these two types were selected as the transferring materials. An effort was also made to select a representative range of recipient clothing to which the labelled fibres would be transferred. The six items chosen were three woollen jackets of varying surface appearance, one acrylic and one wool/nylon sweater and one cotton laboratory coat. Although these were all items of men's clothing there is no reason to believe that materials with similar characteristics are not worn by women. This paper describes the number and size distribution of fibres which were transferred from wool and acrylic materials to different recipient garments for various areas of contact, different pressures and for consecutive contact passes.
Experimental Textile Materials used for Transference The two woollen sweaters and one handknitted square of acrylic material which were used for transference are described in Table 1. One of the sweaters had been extensively worn and the other was new, having been purchased for the experiments from a large chain store. TABLE 1 A DESCRIPTION OF THE TEXTILE MATERIALS USED FOR FIBRE TRANSFERENCE
Source of Material Marks and Spencers sweater Hornes sweater
Paton's 101 Courtelle
Identification Mark Description Fluorescent Labelling t~ A natural Shetland Fluorescein Wool sweater purchased for the experiments t2 A pale brown fine Fluorescein wool sweater which had been extensively worn t3 A red square which Dye in fibre already had recently been shows an intense hand knitted red fluorescence
Fluorescent Labelling The woollen sweaters were labelled with fluorescent dye by immersion in a concentrated solution of sodium fluorescein at 50°C for 30 minutes, they were then washed in running water to remove excess dye and air dried. The acrylic knitting material was red in colour and the dyestuffs present already showed an intense red fluorescence. Recipient Garments The six recipient garments used in the transfer experiments are described in Table 2. The garments were of different manufacture, composition and surface appearance. Some were purchased for the experiments while others had already been worn for a considerable period. TABLE 2
A DESCRIPTION O F T H E SIX RECIPIENT GARMENTS T O WHICH FIBRES WERE TRANSFERRED Recipient Garment Jacket
Manufacturer Daks
Fibre Type Wool
Sweater
Handknitted
Wool/nylon
rz
A bulky green sweater which had been worn for 1 year
Sweater
Harry Fenton
Courtelle Acrylic
r3
A fine yellow sweater which had been worn for 2 years
Jacket
Hepworths
Wool
r4
A typical jacket from a two-tone blue suit which had been worn for 1 year
Jacket
Guards
Wool
r5
A fine brown-checked sports coat which was purchased new for experiments
Cotton
r~
A normal white laboratory coat which had been worn for 2 years
Laboratory Coat Johnson and Sons
Identification Mark Description rl A multi-coloured check tweed jacket purchased new for experiments
Standard Method of Contact Unless otherwise stated the transferring materials were pinned to a 14cm x 14cm expanded polystyrene block and this was pressed by hand against the recipient garment which was placed on a laboratory bench. The block was then pulled across the recipient garment for a distance of 30cm a t a constant pressure. Pressure Two levels of pressure were applied by hand during the various contacts. The low pressure was approximately 30kg/m2and the high pressure approximately 300kg/m2. Repeated Contact Passes During the experiments the selected area of the transferring material was repeatedly pulled across the recipient garments for up to eight consecutive contact passes. The fibres were removed manually or by gentle application of adhesive tape between each contact pass. Fibre Length The approximate length of each transferred fibre was recorded in one of the following size ranges: 0.5-2mm, 2-5mm, 5-10mm and greater than 1Omm.
Recording of Results The recipient garments were examined under a lamp fitted with two 4ft long Phillips T L 4 0 ~ 1 0 8ultraviolet tubes which enabled fibres of more than 0.5mm in length to be counted and recorded. Identification of Factors The various factors in the experiments were identified as follows: T=the effect of transferring material. (The three transferring materials used were identified as t,, t, and t, and are described in Table 1.) R=the effect of recipient garment. (The six recipient garments were identified as r,, r 2 . . . r, and are described in Table 2.) P=the effect of pressure. (The low pressure (30kg/m2)was identified as p, and the high pressure (300kg/ my-. as p,.) C=the effect of repeated contact passes. (The first contact pass was identified as c, and subsequent passes as c,, c, . . . c,.) L=the effect of fibre length. (The smallest size classification was identified as 1, and the larger ones as l 2 . . . 14.) First order interactions were identified from the appropriate effects, e.g. the interaction between pressure and recipient garment was identified as PR. 1
\
Preliminary Investigation Reverse Transference The possibility was investigated that under the conditions used, fibres which were transferred on earlier contact passes could return to the transferring material during subsequent passes. Fibres were transferred from wool sweater t,, using the standard contact procedure and high pressure p,, to the surface of recipient garments r,-r,. After the number of fibres had been recorded a n exactly similar but non-fluorescent sweater was pulled over the same area using similar conditions. The number of fibres which were transferred back to the sweater was then determined. The percentage of fibres which showed this reverse transference from the various recipient garments are shown in Table 3. During the subsequent experiments the fibres were removed after each contact pass thus eliminating this effect. TABLE 3 THE PROPORTION O F FIBRES FROM THE FIRST CONTACT PASS WHICH WERE REVERSE TRANSFERRED DURING THE SECOND PASS FOR DIFFERENT RECIPIENT GARMENTS Recipient Garment
Proportion of Fibres Reverse Transferred (%) 37 41 44 44 60
Area of Contact The number of fibres transferred to garment r, from the wool sweater t, was determined at high pressure p, for square contact areas of 30cm2, 110cm2and 202cm2. The standard contact conditions were used and the results obtained are shown graphically in Figure 1. I t would be reasonable to expect that the number of fibres transferred would be proportional to the area of contact but the number transferred increased
more slowly than this in practice (Figure 1). There are probably two causes for this behaviour. One is that the extent of reverse transference increases with the area of contact and the other is that it is more difficult to ensure complete contact over large areas of two garments than over small areas. On the basis of these results a contact area 14cm x 14cm was chosen for future experiments.
0
r
I
AREA
a
100 OF CONTACT
I
h
200
ctv12
Figure 1. Number of fibres transferred from wool sweater t, to jacket r, at pressure p, plotted against area of contact.
Investigation of Important Factors in Wool Transference The effect of pressure, recipient garment, fibre size and repeated contact passes and their first order interactions were investigated for wool fibres using a balanced four-way classification experiment (Kendall and Stuart, 1966). The variables examined were, two levels of pressure, six recipient garments, eight repeated contact passes and four levels of fibre length making a total of 384 treatment combinations. The new woollen sweater t, was used throughout as the transferring material in this experiment because twelve identical areas of 14cm x 14cm were required and only this garment was sufficiently homogeneous. The outer surface of the transferring garment t1 was divided into twelve identical areas and each area was allocated to a pressure/garment combination. The experiment was deliberately arranged so that the high and low pressure contacts on the same recipient garment were always performed using outer areas of the transferring sweater tl but on different sides, and at different relative locations. The eight contact passes were conducted in the standard manner and the fibres were counted and removed before the next contact pass.
The total number of fibres observed for the ninety-six treatment combinations of pressure recipient garment and contact pass number is shown in Table 4 and the size distribution of the fibres is shown in Table 5 . TABLE 4 THE NUMBER OF FIBRES TRANSFERRED FROM MATERIAL t. FOR NINETY-SIX TREATMENT COMBINATIONS OF PRESSURE, R E ~ I P I E N T GARMENT AND REPEATED CONTACT PASSES Pressure
Recipient Garment
Contact Pass Number c,
c2
c,
re
70 1 290
41 1 213
27 4 121
ro
6 1 2 548 443
c4
c,
c,
c,
c,
Total
18 3 59
13 5 77
236 37 1052
2 1 4 314 342
61 3201
A.
ra
Total
Total
1
5 393
20 2
98
25 4
3 421
102
7 373
22 4
92
2 367
4
TABLE 5 THE SIZE DISTRIBUTION OF TRANSFERRED WOOL FIBRES FOR TWO DIFFERENT PRESSURES AND SIX RECIPIENT GARMENTS (percentages in brackets) Premre
Recipient Garment
11
Fibre Length 1z 1s
14
Treatment of Results The effects and first order interactions were investigated by a n analysis of variance as described by Kendall and Stuart (1966). The laboratory coat r, was excluded from this statistical analysis since the number of fibres transferred to it was always small and the results for this garment were obviously not typical simply by inspection. No replication was possible because the properties of the transferring sweater changed with the number of contact passes, and therefore the residual from the third order interaction was used to test the significance of each effect and first order interaction by means of the F distribution tables which were entered with the appropriate degrees of freedom. The results of the analysis of variance, excluding the laboratory coat r, are shown in Table 6.
TABLE 6 ANALYSIS O F VARIANCE FOR THE EFFECTS O F PRESSURE (P), RECIPIENT GARMENT (R), REPEATED CONTACT PASSES (C), FIBRE SIZE (L) AND THEIR FIRST ORDER INTERACTIONS
Source of Vaiiatwn P R C L PR PC PL RC
Degrees of Freedom 1 4
CL Residual
21 229
Sum of Squares 14,218 1,602 3.72 1
7
Mean Square 14,218 40 1 532
Significancne Level
*** *** ***
3 4
7 3 28
=99%;
NS=not significant at 5% level.
Discussion Table 6 shows that the effects of pressure P, recipient garment R, contact pass number C, fibre length L and the interaction between pressure-fibre length PL and recipient garment-fibre length RL are all highly significant. The number of fibres transferred increased with pressure, the grand total of fibres transferred at the higher pressure p, being about three times that at the lower pressure p, as shown in Table 4.
FIBRE LENGTH M M
P2 Figure 2.
PI
Comparison of size distribution of fibres transferred to jacket r, at pressures p, and p,. 23
A significantly larger number of fibres were observed on some recipient garments than on others. Table 4 shows that at both high and low pressures the largest number of fibres was found on recipient garment r, followed by r,, r,, r3, r 2 and r,. The number of fibres transferred decreased as the contact pass number increased and as can be seen from the column totals in Table 4 the number of fibres transferred in the eighth pass c, was about half that for the first pass c,. The effect of fibre length L is significant but this simply reflects the fact that all the categories of fibre size are not equally populated. The interaction between pressure and fibre length PL can be interpreted with reference to Table 5 since the proportion of fibres which are larger than lOmm is greater a t low pressure than at high pressure. This is demonstrated graphically in Figure 2 for recipient garment r,. The highly significant interaction between recipient garment and fibre length R L can be interpreted with reference to Table 5 since the size distribution of fibres is seen to vary from one recipient garment to another. This interaction is demonstrated graphically in Figure 3 by comparing the size distribution of fibres found on jacket r, with that for the laboratory coat r,. Predominantly short fibres were found on the jacket whereas most fibres on the laboratory coat were much larger. The laboratory coat r, was not included in the overall statistical analysis but Tables 4 and 5 show that this garment produced results which were quite different from the other 5 recipient garments. The number of fibres transferred to the laboratory coat was always low and increased only moderately with pressure (Table 4). The majority of fibres observed on this garment were longer than 5mm (Figure 3) and the number transferred varied erratically with the contact pass number (Table 4). A Comparison of Transferring Materials A further experiment was conducted in order to determine if the results already obtained for transferring sweater t, were typical of sweaters in general. The transferring materials compared were the original woollen sweater t,, a fine woollen sweater which had been extensively worn t, and a square of recently knitted acrylic material t,. The comparison was performed using a balanced three-way classification experiment, the variables being the three transferring garments, two recipient garments (the jacket r, and the sweater r,) and two repeated contact passes, making a total of twelve treatment combinations. The contact passes were performed in the standard manner. The fibres were counted and removed before the second contact pass. The number of fibres transferred for each of the twelve treatment combinations is shown in Table 7. TABLE 7 THE NUMBER O F FIBRES TRANSFERRED AT HIGH PRESSURE (P,) FOR TWELVE TREATMENT COMBINATIONS O F TRANSFERRING MATERIAL, RECIPIENT GARMENT AND REPEATED CONTACT PASSES Recipient Garment
Transferring Garment t1
rl
=3
t, t3 Total
Contact Pass Number CI
138 169 148 455
C2
107 117 164 388
Total 245 286 312 843
tl t2 t3 Total
Treatment of Results The effects and first order interactions were investigated by an analysis of variance as described previously and the results are shown in Table 8.
TABLE 8 ANALYSIS OF VARIANCE FOR THE EFFECTS OF TRANSFERRING MATERIAL (T), RECIPIENT GARMENT (R), REPEATED CONTACT PASSES (C) AND THEIR FIRST ORDER INTERACTIONS IN FIBRE TRANSFERENCE Source of Variation T R C TR TC RC Residual
*=95%;
Degrees of Freedom
Sum of Squares
Mean Square
Significance Level
NS=not significant at 5% level.
Discussion Table 8 shows that the effects of recipient garment R and contact pass C are significant at the 5% level but the effect of transferring material and the first order interactions are not significant. In this smaller experiment the effect of recipient garment and contact pass number have been confirmed. Although there is some variation in the number of fibres observed for different transferring materials (Table 7) this variation is not significant at the 5% level and thus there is no reason to believe that the woollen sweater t, is in any way unrepresentative of sweaters in general. General Discussion The current understanding of fibre transference is based on concepts which were formulated more than forty years ago but these have not been studied experimentally. The fibres are usually thought of as being loose on the surface of the transferring garment and are therefore capable of being shed during contact. Such concepts cannot adequately explain the results obtained in this study. It seems likely that fibres are being continuously transferred from the transferring garment to the recipient garment and vice versa during each contact pass. In the main four-way classification experiment fibres were removed after each contact thus eliminating reverse transference during subsequent passes and therefore the values recorded in Table 4 probably overestimate slightly the number of fibres which would be transferred in a normal contact. The number of wool fibres transferred increased with the area of contact (Figure 1) but not in direct proportion. This effect could be due to reverse transference which occurs during each contact pass so that for large areas of contact there is a greater opportunity for transferred fibres to return to the garment of origin than for smaller areas. However, such effects are likely to be small compared with other variations such as pressure and recipient garment. The number of fibres transferred increased with pressure and decreased with consecutive contact passes. Such results are not unexpected but it is surprising that the number transferred from the three transferring materials (Table 1) varied only slightly whereas the number of fibres found varied considerably from one recipient garment to another (Table 4). As anticipated very few fibres were transferred to the smooth cotton laboratory coat and those fibres which were found showed a very different size distribution from that observed on the other recipient garments (Figure 3). This shows that the mechanism of fibre transfer for the laboratory coat is fundamentally different from the mechanism for the other garments. The interaction observed betwe& pressure and fibre length shows that a higher proportion of short fibres are found at high pressure than at low pressure and this suggests that fibres are being fragmented during each contact. If this is so it would also explain the interaction between recipient garment and fibre
length as the rough garments would be expected to cause more fragmentation, ie, more short fibres, than the smooth garments. In this event the differences observed between the laboratory coat and the other garments (Figure 3) may simply reflect the fact that very little fragmentation can occur on such a smooth garment. The mechanisms which produce fibre transference have been investigated further and the results will be reported later.
FIBRE LENGTH MM
R4
R6
Figure 3. Comparison of size distribution of fibres transferred to jacket r, and laboratory coat r, at pressure p,.
As in these experiments the conditions had to be controlled, it was necessary to use simulated rather than real life contacts. Subject to these and other limitations, the results in Table 4 should allow working estimates to be made for the number of fibres which are likely to be transferred from sweaters during their contact with other garments. In casework there is almost always a delay, sometimes of several days, between the contact at the scene of crime and a suspect being apprehended. I t is therefore not only of interest to estimate, albeit crudely, the number of fibres which would have been transferred originally but also to estimate how many of these would have been lost during subsequent wear. The persistence of wool and acrylic fibres has been determined during wear on the six recipient garments described in these experiments and the results are described in a further paper (Pounds and Smalldon, 1975).
Acknowledgements The authors wish to thank Mr. V. J. Emerson for advice and criticism during the project. We are particularly indebted to Mr. I. W. Evett, West Midlands Forensic Science Laboratory, for his assistance with the statistical analysis.
References FREI-SULTZER, M., 1951, Kriminalistik, 17/18, 190. KENDAL, M. G., and STUART, A., 1966, The Advanced Theory of Statistics, Vol. 3, p.38, Griffen, London KIRK,P. L., 1949, J.Crim.Law and Criminal., 40, 362. KIRK,P. L., 1953, Crime Investigation, p.38, Interscience, New York. LOCARD, E., 1928, Police J., 1, 177. LOCARD, E., 1930, Amer.J . of Pol.Sci., 1, 276. NICKOLLS, L. C., 1956, The Scientific Investigation of Crime, p.39, Butterworth, London. K. W., 1975, J. Forens. Sci. Sac., 15, 29. POUNDS, C. A., and SMALLDON, TRYHORN, F. G., 1935, Police J., 8, 401.
