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Feathering of footwear
PROCEEDINGS
Feathering of footwear RJ DAVIS and A KEELEY The Forensic Science Service, Metropolitan Laboratory, 109 Lambeth Road, London SEl 7LP, United Kingdom A paper presented at the Trace Marks Workshop of the Second Joint Meeting of the Californian Association of Criminalists and the Forensic Science Society, 10th July 1997, Harrogate, (Meeting report in Science & Justice 1998; 38 (2): 128-134).
Introduction Traditionally, the process of establishing that a known item of footwear has made a crime-scene shoemark relies on a combination of (a) class characteristics related to manufacture and (b) wear characteristics caused by erasure of, and damage to, the outsole. The process has been called 'footwear identification' [1,2]. Footwear examiners in the Forensic Science Service (FSS) and elsewhere have known for some time that outsoles can develop microscopic scuff patterns having a branched, ridged appearance after a period of general wear. This type of pattern is believed to be characteristic of an individual outsole and has often been used in casework footwear comparisons to assist identification in conjunction with other accidental damage. Similar scuff patterns had been noted on vehicle tyres in the 1950s, when Schallamach published his seminal papers on abrasion patterns [3,4]. In the Rubber Industry the term 'Schallamach Pattern' is commonly used to describe this type of abrasion pattern. In this paper we shall use the term 'feathering' to apply to the Schallamachtype scuff detail found on worn footwear outsoles. The potential value of feathering on footwear is in its apparently random nature, which offers the possibility of attributing very small portions of a crime-scene footwear mark to a particular outsole. Sharein, for example, found that the feathering pattern on a small area of a footwear mark taken from a burglary scene was indistinguishable from part of the outsole of the suspect's shoe. He pointed to the need for a detailed study into the occurrence and development of such patterns [5]. During 1995 we undertook studies on feathering at the Metropolitan Police Forensic Science Laboratory (now the Forensic Science Service Metropolitan Laboratory). We wished first to c o n f i i the cause of feathering on footwear, to scope its properties and determine how feathering patterns change with time. By then comparing feathering patterns within groups of worn outsoles, we set out to establish whether they might be used on their own as a means of footwear identification. Initially, the records of all casework footwear comparisons undertaken in the MPFSL from 1991 to 1994 were scrutinised. In 28 out of 258 mark-to-outsole identifications, feathering had been taken into account when drawing the conclusion. We also found that many of the prints in the Metropolitan Laboratory Footwear Index (a collection of Science & Justice 2000; 40(4): 273-276
thousands of impressions from footwear outsoles, mainly from casework submissions) showed feathering on all the worn areas of the outsole, but mainly around the heel and toe. Figure 1 is an example of a Footwear Index print, showing a Footwear Index impression of the heel of a Reebok outsole at actual size and at x 3.5 magnification. The ridge spacing in feathering patterns varied from about 0.05mm (50 microns, roughly the diameter of a human hair) to 0.5mm, and feathering could be classified broadly on this basis as fine, medium and coarse. Figure 2 shows examples of fine and coarse feathering. The direction of feathering ridges was fairly consistent, progressing horizontally across the sole, curving upwards at the edge of the heel and downwards at the edge of the toe. The outsole design did not seem to affect the direction of the ridges, but where studs formed part of the pattern, the outer studs quite often had edges of very coarse feathering which could be in a different direction to the rest of the pattern. On some very worn outsoles, the feathering was lost either by becoming very fine and fragmented or the outsole being worn smooth.
Experimental Materials and Methods The method of making outsole test impressions had a crucial effect on the clarity of the feathering patterns in the impressions. Several techniques were tried, including inking, powdering or spraying the outsole with WD40 and taking impressions on paper, clear polyester film or adhesive film. We found that the easiest and most reliable method was as follows. Brush the outsole with a 12.5 mm
FIGURE 1 Heel of Reebok outsole shown at actual size (left) and at x 3.5 magnification (right) to show traditional accidental damaee and feathering. 273
Feathering of footwear
a number of footwear manufacturers. The test piece was affixed with double sided adhesive tape to a 12-inch (300 mm) ruler which was rested on the abrasive paper with a weight on it. The cylinder was rotated by hand and the number of revolutions counted. Lead metal weighing 1.2 kilograms was used as the weight for 400 mm2test pieces. The experimental set-up is shown diagrammatically in Figure 3. Test pieces from Hi-Tec and Dunlop athletic training shoe outsoles were abraded under the same conditions (i.e. the same weight applied for the same number of revolutions). Pairs of test pieces from the same area of outsoles made in
-
rotating 1 cylinder
'abrasive paper
FIGURE 3 Side view of the controlled abrasion rig for producing artificial feathering.
FIGURE 2 Fine feathering on a Reebok 'Classic' circular stud (top) and coarse feathering on an Itshide 'Commando' heel bar (bottom), shown at x 25 magnification.
(112-inch) paintbrush loaded with fine carbon black powder (Raven Black 5000, Columbian Chemical Co, USA), make an impression on clear, self-adhesive film and then seal this with a sheet of clear, non-adhesive, polyester film. The amount of powder affected the clarity of the ridges, as did the pressure applied to the sole when making the impression. Experiments with art$cial abrasion Producing feathering artificially in the laboratory offered the best prospect of determining whether identical feathering patterns could be produced if all conditions were kept constant. We made a large number of attempts to produce feathering, abrading outsoling materials at the bench by rubbing with various grades of sandpaper and carborundum (silicon carbide) paper and even heating the outsole and rubbing it directly against concrete. After a large number of unsuccessful trials, feathering patterns were eventually produced at the laboratory bench by using a hollow cylinder with carborundum abrasive paper (Struers Silicon Carbide Paper No. 1000) wrapped around it. Test pieces 20 x 20 mm were cut from outsoles supplied by
the same mould and the same area of outsoles made in different moulds were abraded and test prints taken after 50, 100, 150 and 200 revolutions. These prints were then compared under a microscope for matching characteristics. We obtained samples of the most common outsole compositions from the Shoe and Allied Trades Research Association (SATRA). The soling materials were: natural crepe rubber, thermoplastic natural rubber (TR), nitrile vulcanised rubber (NBR), styrene-butadiene vulcanised rubber (SBR), polyvinylchloride (PVC) and PVCInitrile blend. We were able to produce feathering on TR and nitrile rubber, but not on crepe rubber, SBR, PVC, or PVCInitrile rubber. We also carried out Fourier Transform Infrared (FTIR) analysis on the outsoles of actual footwear and found that the outsoles of most training shoes were manufactured from natural rubber, regardless of make or colour. Lifetime of feathering Tart and his colleagues studied the appearance and disappearance of feathering detail on the outsoles of 27 pairs of Reebok 'Aurora' trainers, each worn from new by a separate volunteer [Matthew Tart, personal communication, 19961. Feathering patterns appeared on all 54 outsoles after 27.5 to 385 hours of wear and were still present on 21 outsoles at the end of the study. On the remaining 33 outsoles, the lifetime of the patterns ranged from 34 to 2655 hours. Science & Justice 2000; 40(4): 273-276
RJ DAVIS and A KEELEY
FIGURE 4 Natural feathering on a Reebok outsole (left) and fingerprint ridge detail (right) with a 1 mm grid.
Comparisons were made, but no positive matches could be found between subsequent impressions from the same sole. In our study, the same person wore each of four pairs of Dunlop shoes for varying lengths of time. All the left outsoles had been produced from one mould and all the right outsoles from another. Test prints were taken of the soles at regular intervals to determine the approximate time of the initial appearance of feathering detail and the length of time it took to change. Further prints were initially taken on a daily or longer basis. The prints from different pairs of these shoes were compared at equivalent stages of wear and any similarities noted. Chance match studies The physical appearance of feathering, with its branching ridges, is not unlike that of fingerprints (Figure 4). A study of the fingerprint classification system used in the UK yielded a basis for classifying feathering patterns. First, enlarged areas of marks were scanned by eye for the occurrence of feathering features or combinations of features from a pre-defined list of feature types. This was based loosely on the fingerprint ridge characteristics e.g. ridge ending, bifurcation, lake, crossover. When a similar combination of features in two different impressions was noted a careful direct comparison was then made between the two, extending the area of interest outward from the locus of similarity. Chance match studies were carried out on test strips from Hi-Tec outsoles subjected to mechanical abrasion, on a number of worn Itshide 'Commando' heel units, on the Dunlop shoes described above and on a set of Reebok 'Classic' outsole impressions from the Footwear Index.
Results Artificial abrasion tests First of all, prints from the same test piece after different numbers of revolutions of the abrasion device were compared to determine whether or not feathering detail changed with the degree of abrasion. We found that the form of the detail was clearly different at each stage (Figure 5). Science & Justice 2000; 40(4): 273-276
FIGURE 5 Controlled abrasion of a HiTec rubber outsole test strip after 50 (top) and 150 (bottom) revolutions, shown at x 10 magnification].
FIGURE 6 Controlled abrasion of HiTec rubber outsole test strips after 200 revolutions with a 1 mm scale.
Comparisons were then made of test pieces taken from the same area of Hi-Tec outsoles produced from the same mould and different moulds. There were occasional chance matches of individual features in different test strips, but features that did not match always surrounded these. In all 60 such comparisons were carried out.
Feathering of footwear
A B C D E F G H I
-
J K L M1
A B C D E F G H I , J-KLM
-----
,
,
1
FIGURE 7 Feathering on the heel of a Dunlop outsole before to^) and after (bottom) running one mile with a 0.2mm grid.
A significant chance match was not found even when the test pieces were taken from exactly the same area of different outsoles produced from the same mould and subjected to identical abrasion. This is illustrated in Figure 6 which shows test strips cut from the same place on each of three outsoles produced in the same mould. Lifetime of feathering and chance matching The first prints from the four pairs of new Dunlop trainers worn by the same person were taken after time lapses of between six hours and 34 hours wear. Definite feathering patterns appeared on two outsoles after less than nine hours wear. The pattern detail began to change after 3112 hours extra wear on one outsole and nine hours on the other and was completely different after six hours on one and 16 hours on the other. In all, there were 16 comparisons between areas of feathering on the different Dunlop outsoles to ascertain the degree of chance matching. Forty-five comparisons of feathering detail were carried out on different Reebok 'Classic' Footwear Index impressions and 150 comparisons between impressions of different Itshide 'Commando' heel units. In all instances, although occasional similarities between individual features were found, these were always surrounded by clear differences.
Discussion The main purpose of these studies was to establish the uniqueness or otherwise of feathering (Schallamach patterns) on footwear outsoles. Accidental damage characteristics result from individual events, but feathering seems to derive from a single extended event, the continuous process of abrasion to the outsole fabric caused by wear. By producing feathering in the laboratory we kept the number of variables to the minimum. Having confirmed that the patterns on footwear outsoles were caused by abrasion we were able to go on to address the underlying question by carrying out a series of chance match analyses involving both artificial and natural feathering. Results of comparing the mechanically-producedfeathering showed that a significant match was not found even when the test pieces, taken from the same area of different outsoles produced in the same mould, were subjected to the same abrasion regimen. Also, a significant chance match could not be found between training shoes, produced in the same mould and worn for the same length of time by the same person. In fact, on every occasion when two apparently matching characteristics were found in impressions from different outsoles, they were surrounded by nonmatching characteristics. With perfect impressions, only an area three features square should be necessary for a positive identification or elimination. However, in real-life feathering patterns change in only a few hours with wear and crime-scene marks are often indistinct. Features may be obscured and ridge detail may not be discernible due to a lack of clarity in a mark. Figure 7 shows prints taken of the same area of a Dunlop outsole before and after the wearer of the shoe had run one mile. The two are still clearly a match even after the extra wear, but if we had not known that they were made by the same shoe, what area of match would have been needed to conclude identity? The actual size of the area illustrated, which is replete with feathering characteristics, is about 2 rnm x 3 mm. In other words, with crime marks showing the level of definition illustrated, an area just a few millimetres square will suffice. Acknowledgements The authors would like particularly to thank Phil Evans and Hazel Wilson, two undergraduate students on placement at the Metropolitan Police Forensic Science Laboratory in 1995, who carried out much of the practical work described here. We are also very grateful to the manufacturers who supplied the footwear and outsole samples used in these experiments. References 1. Cassidy MJ. Footwear identification. Canadian Government hinting Centre, 1980. 2. Bodziak WJ. Footwear impression evidence: Detection, recovery and examination (2nd ed.). CRC Press LLC, Boca Raton, 1999 3. Schallamach A. Abrasion pattern on rubber. Transactions of the Institute of Rubber Industries 1952; 28: 256268 4. Schallamach A. Friction and abrasion of rubber. Wear 1958; 1: 384417 5. Sharein R. Rainy Day Ident. Royal Canadian Mounted Police Gazette, Vo1.55, No.78~8,1993.
Science & Justice 2000; 40(4): 273-276
Feathering of footwear RJ DAVIS and A KEELEY The Forensic Science Service, Metropolitan Laboratory, 109 Lambeth Road, London SEl 7LP, United Kingdom A paper presented at the Trace Marks Workshop of the Second Joint Meeting of the Californian Association of Criminalists and the Forensic Science Society, 10th July 1997, Harrogate, (Meeting report in Science & Justice 1998; 38 (2): 128-134).
Introduction Traditionally, the process of establishing that a known item of footwear has made a crime-scene shoemark relies on a combination of (a) class characteristics related to manufacture and (b) wear characteristics caused by erasure of, and damage to, the outsole. The process has been called 'footwear identification' [1,2]. Footwear examiners in the Forensic Science Service (FSS) and elsewhere have known for some time that outsoles can develop microscopic scuff patterns having a branched, ridged appearance after a period of general wear. This type of pattern is believed to be characteristic of an individual outsole and has often been used in casework footwear comparisons to assist identification in conjunction with other accidental damage. Similar scuff patterns had been noted on vehicle tyres in the 1950s, when Schallamach published his seminal papers on abrasion patterns [3,4]. In the Rubber Industry the term 'Schallamach Pattern' is commonly used to describe this type of abrasion pattern. In this paper we shall use the term 'feathering' to apply to the Schallamachtype scuff detail found on worn footwear outsoles. The potential value of feathering on footwear is in its apparently random nature, which offers the possibility of attributing very small portions of a crime-scene footwear mark to a particular outsole. Sharein, for example, found that the feathering pattern on a small area of a footwear mark taken from a burglary scene was indistinguishable from part of the outsole of the suspect's shoe. He pointed to the need for a detailed study into the occurrence and development of such patterns [5]. During 1995 we undertook studies on feathering at the Metropolitan Police Forensic Science Laboratory (now the Forensic Science Service Metropolitan Laboratory). We wished first to c o n f i i the cause of feathering on footwear, to scope its properties and determine how feathering patterns change with time. By then comparing feathering patterns within groups of worn outsoles, we set out to establish whether they might be used on their own as a means of footwear identification. Initially, the records of all casework footwear comparisons undertaken in the MPFSL from 1991 to 1994 were scrutinised. In 28 out of 258 mark-to-outsole identifications, feathering had been taken into account when drawing the conclusion. We also found that many of the prints in the Metropolitan Laboratory Footwear Index (a collection of Science & Justice 2000; 40(4): 273-276
thousands of impressions from footwear outsoles, mainly from casework submissions) showed feathering on all the worn areas of the outsole, but mainly around the heel and toe. Figure 1 is an example of a Footwear Index print, showing a Footwear Index impression of the heel of a Reebok outsole at actual size and at x 3.5 magnification. The ridge spacing in feathering patterns varied from about 0.05mm (50 microns, roughly the diameter of a human hair) to 0.5mm, and feathering could be classified broadly on this basis as fine, medium and coarse. Figure 2 shows examples of fine and coarse feathering. The direction of feathering ridges was fairly consistent, progressing horizontally across the sole, curving upwards at the edge of the heel and downwards at the edge of the toe. The outsole design did not seem to affect the direction of the ridges, but where studs formed part of the pattern, the outer studs quite often had edges of very coarse feathering which could be in a different direction to the rest of the pattern. On some very worn outsoles, the feathering was lost either by becoming very fine and fragmented or the outsole being worn smooth.
Experimental Materials and Methods The method of making outsole test impressions had a crucial effect on the clarity of the feathering patterns in the impressions. Several techniques were tried, including inking, powdering or spraying the outsole with WD40 and taking impressions on paper, clear polyester film or adhesive film. We found that the easiest and most reliable method was as follows. Brush the outsole with a 12.5 mm
FIGURE 1 Heel of Reebok outsole shown at actual size (left) and at x 3.5 magnification (right) to show traditional accidental damaee and feathering. 273
Feathering of footwear
a number of footwear manufacturers. The test piece was affixed with double sided adhesive tape to a 12-inch (300 mm) ruler which was rested on the abrasive paper with a weight on it. The cylinder was rotated by hand and the number of revolutions counted. Lead metal weighing 1.2 kilograms was used as the weight for 400 mm2test pieces. The experimental set-up is shown diagrammatically in Figure 3. Test pieces from Hi-Tec and Dunlop athletic training shoe outsoles were abraded under the same conditions (i.e. the same weight applied for the same number of revolutions). Pairs of test pieces from the same area of outsoles made in
-
rotating 1 cylinder
'abrasive paper
FIGURE 3 Side view of the controlled abrasion rig for producing artificial feathering.
FIGURE 2 Fine feathering on a Reebok 'Classic' circular stud (top) and coarse feathering on an Itshide 'Commando' heel bar (bottom), shown at x 25 magnification.
(112-inch) paintbrush loaded with fine carbon black powder (Raven Black 5000, Columbian Chemical Co, USA), make an impression on clear, self-adhesive film and then seal this with a sheet of clear, non-adhesive, polyester film. The amount of powder affected the clarity of the ridges, as did the pressure applied to the sole when making the impression. Experiments with art$cial abrasion Producing feathering artificially in the laboratory offered the best prospect of determining whether identical feathering patterns could be produced if all conditions were kept constant. We made a large number of attempts to produce feathering, abrading outsoling materials at the bench by rubbing with various grades of sandpaper and carborundum (silicon carbide) paper and even heating the outsole and rubbing it directly against concrete. After a large number of unsuccessful trials, feathering patterns were eventually produced at the laboratory bench by using a hollow cylinder with carborundum abrasive paper (Struers Silicon Carbide Paper No. 1000) wrapped around it. Test pieces 20 x 20 mm were cut from outsoles supplied by
the same mould and the same area of outsoles made in different moulds were abraded and test prints taken after 50, 100, 150 and 200 revolutions. These prints were then compared under a microscope for matching characteristics. We obtained samples of the most common outsole compositions from the Shoe and Allied Trades Research Association (SATRA). The soling materials were: natural crepe rubber, thermoplastic natural rubber (TR), nitrile vulcanised rubber (NBR), styrene-butadiene vulcanised rubber (SBR), polyvinylchloride (PVC) and PVCInitrile blend. We were able to produce feathering on TR and nitrile rubber, but not on crepe rubber, SBR, PVC, or PVCInitrile rubber. We also carried out Fourier Transform Infrared (FTIR) analysis on the outsoles of actual footwear and found that the outsoles of most training shoes were manufactured from natural rubber, regardless of make or colour. Lifetime of feathering Tart and his colleagues studied the appearance and disappearance of feathering detail on the outsoles of 27 pairs of Reebok 'Aurora' trainers, each worn from new by a separate volunteer [Matthew Tart, personal communication, 19961. Feathering patterns appeared on all 54 outsoles after 27.5 to 385 hours of wear and were still present on 21 outsoles at the end of the study. On the remaining 33 outsoles, the lifetime of the patterns ranged from 34 to 2655 hours. Science & Justice 2000; 40(4): 273-276
RJ DAVIS and A KEELEY
FIGURE 4 Natural feathering on a Reebok outsole (left) and fingerprint ridge detail (right) with a 1 mm grid.
Comparisons were made, but no positive matches could be found between subsequent impressions from the same sole. In our study, the same person wore each of four pairs of Dunlop shoes for varying lengths of time. All the left outsoles had been produced from one mould and all the right outsoles from another. Test prints were taken of the soles at regular intervals to determine the approximate time of the initial appearance of feathering detail and the length of time it took to change. Further prints were initially taken on a daily or longer basis. The prints from different pairs of these shoes were compared at equivalent stages of wear and any similarities noted. Chance match studies The physical appearance of feathering, with its branching ridges, is not unlike that of fingerprints (Figure 4). A study of the fingerprint classification system used in the UK yielded a basis for classifying feathering patterns. First, enlarged areas of marks were scanned by eye for the occurrence of feathering features or combinations of features from a pre-defined list of feature types. This was based loosely on the fingerprint ridge characteristics e.g. ridge ending, bifurcation, lake, crossover. When a similar combination of features in two different impressions was noted a careful direct comparison was then made between the two, extending the area of interest outward from the locus of similarity. Chance match studies were carried out on test strips from Hi-Tec outsoles subjected to mechanical abrasion, on a number of worn Itshide 'Commando' heel units, on the Dunlop shoes described above and on a set of Reebok 'Classic' outsole impressions from the Footwear Index.
Results Artificial abrasion tests First of all, prints from the same test piece after different numbers of revolutions of the abrasion device were compared to determine whether or not feathering detail changed with the degree of abrasion. We found that the form of the detail was clearly different at each stage (Figure 5). Science & Justice 2000; 40(4): 273-276
FIGURE 5 Controlled abrasion of a HiTec rubber outsole test strip after 50 (top) and 150 (bottom) revolutions, shown at x 10 magnification].
FIGURE 6 Controlled abrasion of HiTec rubber outsole test strips after 200 revolutions with a 1 mm scale.
Comparisons were then made of test pieces taken from the same area of Hi-Tec outsoles produced from the same mould and different moulds. There were occasional chance matches of individual features in different test strips, but features that did not match always surrounded these. In all 60 such comparisons were carried out.
Feathering of footwear
A B C D E F G H I
-
J K L M1
A B C D E F G H I , J-KLM
-----
,
,
1
FIGURE 7 Feathering on the heel of a Dunlop outsole before to^) and after (bottom) running one mile with a 0.2mm grid.
A significant chance match was not found even when the test pieces were taken from exactly the same area of different outsoles produced from the same mould and subjected to identical abrasion. This is illustrated in Figure 6 which shows test strips cut from the same place on each of three outsoles produced in the same mould. Lifetime of feathering and chance matching The first prints from the four pairs of new Dunlop trainers worn by the same person were taken after time lapses of between six hours and 34 hours wear. Definite feathering patterns appeared on two outsoles after less than nine hours wear. The pattern detail began to change after 3112 hours extra wear on one outsole and nine hours on the other and was completely different after six hours on one and 16 hours on the other. In all, there were 16 comparisons between areas of feathering on the different Dunlop outsoles to ascertain the degree of chance matching. Forty-five comparisons of feathering detail were carried out on different Reebok 'Classic' Footwear Index impressions and 150 comparisons between impressions of different Itshide 'Commando' heel units. In all instances, although occasional similarities between individual features were found, these were always surrounded by clear differences.
Discussion The main purpose of these studies was to establish the uniqueness or otherwise of feathering (Schallamach patterns) on footwear outsoles. Accidental damage characteristics result from individual events, but feathering seems to derive from a single extended event, the continuous process of abrasion to the outsole fabric caused by wear. By producing feathering in the laboratory we kept the number of variables to the minimum. Having confirmed that the patterns on footwear outsoles were caused by abrasion we were able to go on to address the underlying question by carrying out a series of chance match analyses involving both artificial and natural feathering. Results of comparing the mechanically-producedfeathering showed that a significant match was not found even when the test pieces, taken from the same area of different outsoles produced in the same mould, were subjected to the same abrasion regimen. Also, a significant chance match could not be found between training shoes, produced in the same mould and worn for the same length of time by the same person. In fact, on every occasion when two apparently matching characteristics were found in impressions from different outsoles, they were surrounded by nonmatching characteristics. With perfect impressions, only an area three features square should be necessary for a positive identification or elimination. However, in real-life feathering patterns change in only a few hours with wear and crime-scene marks are often indistinct. Features may be obscured and ridge detail may not be discernible due to a lack of clarity in a mark. Figure 7 shows prints taken of the same area of a Dunlop outsole before and after the wearer of the shoe had run one mile. The two are still clearly a match even after the extra wear, but if we had not known that they were made by the same shoe, what area of match would have been needed to conclude identity? The actual size of the area illustrated, which is replete with feathering characteristics, is about 2 rnm x 3 mm. In other words, with crime marks showing the level of definition illustrated, an area just a few millimetres square will suffice. Acknowledgements The authors would like particularly to thank Phil Evans and Hazel Wilson, two undergraduate students on placement at the Metropolitan Police Forensic Science Laboratory in 1995, who carried out much of the practical work described here. We are also very grateful to the manufacturers who supplied the footwear and outsole samples used in these experiments. References 1. Cassidy MJ. Footwear identification. Canadian Government hinting Centre, 1980. 2. Bodziak WJ. Footwear impression evidence: Detection, recovery and examination (2nd ed.). CRC Press LLC, Boca Raton, 1999 3. Schallamach A. Abrasion pattern on rubber. Transactions of the Institute of Rubber Industries 1952; 28: 256268 4. Schallamach A. Friction and abrasion of rubber. Wear 1958; 1: 384417 5. Sharein R. Rainy Day Ident. Royal Canadian Mounted Police Gazette, Vo1.55, No.78~8,1993.
Science & Justice 2000; 40(4): 273-276