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`Journal of Physics D: Applied Physics
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`The deposition of fingerprint films
`
`To cite this article: B Scruton et al 1975 J. Phys. D: Appl. Phys. 8 714
`
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`

`

`J. Phys. D: Appl. Phys., Vol. 8, 1975. Printed in Great Britain. 0 1975
`
`The deposition of fingerprint films
`
`B Scrutont, B W Robins and B H Blott
`Physics Department, University of Southampton, Southampton, SO9 5NH
`
`Received 2 December 1974, in final form 13 January 1975
`
`Abstract. The contact of human fingers with solid surfaces and their subsequent separa-
`tion have been studied microscopically. Scanning electron microscopy and contact
`angle measurements have been applied to examine the deposited film. When a finger
`touches a surface, a film of liquid present on the finger spreads to produce apparent
`contact over much of the fingerprint ridge area. Lifting of the finger causes the film to
`recede and leave a deposit which may be either a distribution of droplets on a thin
`contaminating layer of adsorbed molecules, or a continuous film: which type is depen-
`dent on both the composition of the fingerprint and the nature of the substrate. It is
`shown that the type of behaviour observed in a particular case is determined by the
`contact angle between the liquid film and the contaminated substrate surface: in general
`sebum-rich deposits leave continuous films, whereas eccrine-sweat-rich deposits form
`droplets.
`
`1. Introduction
`
`The importance of fingerprints in the identification of individuals became widely accepted
`towards the end of the last century following the investigations of Faulds, Galton,
`Henry and others (see Bridges 1942). Since then, attention in this field has concentrated
`on the development of latent prints and pattern classification. Of paramount importance
`in the study of fingerprints are the microscopic characteristics of the process by which
`they are deposited. Results of an initial survey of this aspect form the basis of this paper.
`It is a matter of common experience that a layer of contamination remains on a
`surface after it has been touched by a finger. The deposit is often immediately visible
`and clearly shows the papillary ridge pattern, or fingerprint. Even when this is not
`obvious the deposit may cause significant changes in the physical and chemical nature
`of the surface, as exemplified by the enhanced adhesion of small solid particles and the
`decrease in liquid wetting. It is well known in the vapour-deposition of metals that nuclea-
`tion is inhibited by fingerprint contamination. The print also produces striking changes
`in the surface potential (Scruton and Blott 1973) and affects the nucleation of salts from
`solution (Robins et a1 in preparation). Nevertheless the quantity of material involved
`in a fingerprint deposit is small; usually it weighs no more than 10 pg, ie its mean
`thickness is of the order of 0.1 pm.
`In forensic science chemical and physical methods are used to develop latent finger
`deposits (Moenssens 1971). However, the physical principles underlying the transfer
`of material from a finger to a solid surface have only recently become a subject of
`investigation.
`t Now at CEGB Marchwood Engineering Laboratories, Marchwood, Southampton, SO4 4ZB.
`
`714
`
`Reactive Surfaces Ltd. LLP
`Ex. 1045 (Ray Attachment K)
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`

`The deposition of fingerprint films
`
`715
`
`2. Origin and nature of fingerprint material
`
`Before a further discussion of the physical nature of the fingerprint it will be useful to
`summarize the origin and chemical composition of the material which it comprises
`(Kuno 1956, Rothman 1954).
`The moisture of the finger tips originates primarily from sweat secreted by the eccrine
`sweat glands. Though present over most parts of the body, these glands are most
`numerous on the soles of the feet and palms of the hands where their surface density is
`On the finger tips they occur along the papillary ridges at intervals of
`about 4 per "2.
`about 0.5 mm.
`Although eccrine sweat is a dilute aqueous solution the water is rapidly lost by
`evaporation after secretion. The remaining concentrated solution is a complex mixture
`of both inorganic and organic components. The composition of this surface film is
`modified to a variable degree by materials from two other sources: breakdown and
`flaking (desquamation) of the hardened (cornified) surface layer of the skin on the finger
`tips, and surface films covering other areas of the body. In particular, sebaceous and to
`a lesser extent apocrine secretions may be transferred to the finger from the face and
`hair by occasional contact. An outline of the chemical nature of these materials is
`included in the appendix but the data are summarized here in the form of a histogram
`(figure 1); it is apparent that a significant proportion of polar organic material is present
`on the fingers.
`
`Sodium
`Potassium
`Calcium
`Magnesium
`Chloride
`Sulphotc
`Ammonia
`Urea
`Amino-acids
`Lactic acid
`Carbon dioxide
`0
`Concr
`
`Fat1 acids (free L waxes)
`ChoLterol (free i esters)
`Phospholipids
`Squalene 6 other hydrocarbon
`Almhcls*
`Polyhydroxy*
`
`Free fatty acids
`Triglycerides
`Wax esters
`0
`Weight per s
`Proportion by
`Figure 1. (a) Histogram showing the concentrations of the major constituents of eccrine
`sweat. (b) Histogram showing the composition of stratum corneum lipids. The con-
`centrations shown apply specifically to stratum comeum except those marked by an
`asterisk which apply to total epidermal lipid (Reinertson and Wheatley 1959). (c) Histo-
`gram showing the relative abundance of some components of sebum (values taken from
`Peter et a1 1970b).
`
`0
`
`All constituents are removed by washing, after which the materials from the three
`sources are restored at different rates. Whereas the sebaceous secretion (sebum) is
`picked up incidentally the desquamation of the skin is a continuous process but rela-
`tively slow compared with the normal rate of eccrine sweating from the fingers. This
`last is however dependent on the physiological and psychological state of the subject.
`Only a fraction of the liquid film on the fingers is transferred to a surface by contact;
`it is possible, under laboratory conditions, to deposit several prints in succession from
`the same finger without seriously reducing the quantity of material in each.
`
`3. Observations and discussion
`The composition and abundance of the material covering the fingers have been shown to
`be variable; nevertheless, a number of general features can be discerned in the behaviour
`
`57
`
`

`

`716
`
`B Scruton, B W Robins and B H Blott
`
`of the material as it is transferred by contact to a solid surface. These are described in
`the following five sections which deal, in order, with: contact of the finger ridge with a
`surface; the different form the deposits take; stability of the print material with time;
`the determination of contact angles as one of the few physical parameters measurable;
`and the development of a physical model to explain the observed effects.
`
`3. I . Contact area
`The contact of a finger with a solid surface was investigated microscopically. The finger
`was supported in a narrow channel in a plate, which was pivoted at one end on a knife
`edge. At the other end a screw provided for adjustment of tilt. A 9 mm hole in the
`plate allowed part of the finger tip to protrude so that, by adjustment of the screw, con-
`tact was made with a plate of transparent material on the upper surface of which a
`microscope was focused from below.
`The finger ridges are rough on a microscopic scale as is evident from the scanning
`electron micrograph (figure 2, plate) so that true contact with a surface occurs over only
`a small fraction of the apparent ridge area. However, the film of material normally
`present on the ridges suffices to fill much of the space between the ridge and substrate,
`resulting in a large area of apparent contact (figure 3, plate). This area is load-dependent.
`Under a total load on the finger of 0.5 N a typical ridge had a width 125 pm and appar-
`ent contact occurred over 55 % of the ridge area; when the load was increased to 10 N the
`width was 250 pm and the degree of apparent contact 80% (figure 3). Although the
`quantity of moisture on the finger tips varies considerably on different occasions, under
`most conditions it is sufficient to give the results described. However, if the finger is
`artificially dried by being thoroughly washed with acetone a smaller area of apparent
`contact is observed (figure 4, plate). Contact is made at a limited number of points, and
`although the width of the contact area is unchanged the degree of coverage is reduced
`to only 40% or less. The effect of loading the finger is, as before, to increase the width
`of the apparent contact area by producing new points of contact (figure 4). An im-
`portant feature is that the areas of the original contact points are largely unchanged.
`These results indicate that the microscopic ridge surface is not sufficiently deformed by
`the applied pressure to cause the liquid film to be squeezed out; the principal effect of
`pressure is to deform the bulk of the ridge so that more points of contact with the
`substrate are formed.
`In the initial observations (figure 3) no difference could be discerned between the
`points of true contact of the finger with the substrate and the areas of liquid film. This
`is a consequence of the approximate equality of the refractive indices of the skin surface
`and the liquid film. The refractive index of skin was estimated by observing microscopic-
`ally a fine scratch on a glass slide over which had been placed a section of finger ridge of
`thickness 0.15 nim immersed in glycerol (refractive index 1.47). It was observed that the
`section of the scratch covered by the skin and that covered only by glycerol were in
`focus simultaneously, indicating the refractive index of stratum corneum to be 1.47 f 0.03.
`The refractive index of the liquid film lies in the range 1-40-1.54 (Thomas and
`Reynoldson 1975).
`
`3.2. Separation ofJiger surface porn substrate
`The lifting of a finger from a surface causes the meniscus of the sandwiched film to
`recede leaving along each ridge a deposit which for rapid lifting may take the form of
`
`

`

`The deposition of jingerprint jilms
`
`717
`
`either a continuous liquid pool or a distribution of droplets. Experiments have shown
`that both the composition of the surface film and the nature of the substrate determine
`which type of deposit is obtained in a particular case.
`Fingerprints containing mostly eccrine sweat were obtained by washing a finger in
`acetone and then after an interval of several minutes, during which contact of the finger
`with any surface was avoided, depressing it on to the experimental surface. Prints in
`which sebum predominated were taken from fingers which had touched the face immedi-
`ately after being washed in acetone. The sweat-rich prints on all surfaces studied (listed
`in figure 10) had the form of droplets most of which were between 1 and 30 p.m
`in
`diameter (figure 5a, plate). Sebum-rich prints had a similar form to this on glass, mica,
`metals and PTFE (figure 5b). On the remaining surfaces the sebum-rich deposits consisted
`of a more or less continuous pool of liquid containing more solid material (figure 6,
`plate). Prints of uncontrolled composition on this latter group of materials were found
`to take either of the two possible forms and sometimes both occurred in different areas
`of the same print.
`Slow lifting of the finger from the substrate yielded different results from those for
`rapid lifting; each type of substrate produced a similar print for both eccrine-sweat
`and sebum deposits.
`Retraction of the liquid film left relatively few droplets, the bulk of the liquid flowing
`into a small number of islands forming bridges between the finger ridges and substrate.
`With further lifting of the finger the liquid bridges necked and divided to produce large
`isolated droplets (figure 7 , plate).
`
`3.3. Aging of the deposit
`The appearance of a fingerprint deposit changes slowly. Although some droplets are
`observed to evaporate to yield salt crystals within minutes of deposition, most of the
`deposit remains largely unchanged for longer periods. The volume of droplets is known
`to decrease significantly within 18 h of deposition (Thomas and Reynoldson 1975) as
`the more volatile components evaporate. At the same time the viscosity increases, a
`qualitative indication of this change being obtained by drawing a fine stylus over the
`fingerprint observed microscopically. Droplets in a fresh print are highly mobile, but
`after several days they become viscous and almost solid, their surface developing a
`wrinkled appearance (figure 8, plate).
`
`3.4. Contact angles
`Contact angles of fingerprint material freshly deposited on various surfaces were meas-
`ured within a few minutes using a microscope fitted with a tilting stage, illumination
`being through the objective. The method is a microscopic development of the system
`used by Fort and Patterson (1963). The angles of tilt at which selected reflections dis-
`appeared provided a measure of the respective contact angles. Disappearance occurred
`when the extreme edge of the incident light pencil just failed to enter the microscope
`objective (see figure 9).
`For comparison of different surfaces both sweat-rich and sebum-rich prints were
`taken from the same finger. Contact angles for the various surfaces are shown in figure 10.
`The most striking feature of the results is that the contact angles for sweat-rich deposits
`have a higher mean and larger ranges than for the sebum-rich deposits. PTFE exhibits
`the same range of contact angles for both types of deposit and its relatively high values are
`
`

`

`718
`
`B Scruton, B W Robins and B H BIott
`
`( b )
`( C )
`( 0 )
`Figure 9. The optical system for contact angle measurements: (U) The pencil half-angle
`a of the incident beam and the illumination window Won the sample. (b) The situation
`at the point of disappearance of a reflected beam of light from the droplet. Reflections
`from the substrate and from near the edge of the droplet do not enter the objective.
`It is clear that the important beams are at one extreme of the incident pencil of light.
`The tilt from the horizontal is given by ($+ e), where $=+(a+ j3). (c) The relation
`between the pencil half-angle a, the objective half-angle subtended at the sample j3, the
`contact angle 6, and the angle measured from the horizontal ($+ e).
`
`consistent with such a low energy surface. In the case of sebum-rich prints the low-
`energy surfaces actually yield lower contact angles than the high-energy ones, contrary
`to expectations. These results indicate that there is some mediating factor between
`substrate and film. A model involving adsorption of material from the liquid film on to
`the substrate during contact of the finger would account for our observations. Polar
`materials such as long chain fatty acids, and alcohols, are known to adsorb from solution
`on to metals and glass to form close-packed monolayers (Zisman 1964). Free fatty
`acids and sterols are present in the fingerprint material, and it is likely that the spreading
`of this material over the substrate is accompanied by adsorption of these polar con-
`stitutents, though not necessarily uniformly. Any droplets formed by retraction of the
`liquid film then rest on the monolayer (cf the growth of one metal on another, Moss and
`Blott 1969). Therefore, with the possible exception of PTFE and related materials (for
`which adsorption probably does not occur), the contact angles measured are more likely
`to reflect the nature of the contaminant layer than the surface energy of the pure sub-
`strate. The presence of such a layer, of monomolecular thickness, has been inferred
`independently by Thomas and Reynoldson (1 975).
`Direct evidence for the existence of a thin film entirely covering the ridges of depos-
`ited prints is obtained from SEM examination of uncoated prints using a low-energy beam
`at glancing angle. Fingerprints on gold appear as shown in figure 11 (plate); the ridges
`of the print are a better secondary electron emitter under these conditions than the gold
`and although individual droplets are almost indistinguishable the ridges appear as
`continuous pale bands suggesting the presence of an almost uniform film. Such a film
`must be of at least monatomic thickness since the escape depth for secondary electrons
`is approximately 0.5 nm. Similar observations were made on polymethyl methacrylate
`(Perspex), polyethylene and PVC. However, charging of the specimens in the beam re-
`duced the accuracy of observation, particularly in the case of polyethylene where no
`ridges have yet been discerned.
`
`

`

`The deposition of fingerprint films
`
`719
`
`Aluminium
`Glass
`
`Mica
`Ace t o te
`Mylar
`Polyethylene
`Polyurethane
`Nylon
`P V C
`Perspex
`
`P T F E
`Aluminium
`Glass
`Mica
`Acetate
`Mylar
`Polyethylene
`Polyurethane
`Nylon
`P V C
`Perspex
`
`P T F E
`
`' ~ '
`
`'
`
`'
`
`.
`
`"
`
`"
`
`e
`
`'
`
`'
`
`
`
`1
`
`0
`
`'
`
`"
`
`
`'
`l
`I
`'
`20
`IO
`Contact angle 8 (deg)
`Figure 10. Bar chart showing the ranges of contact angles observed on different sub-
`strates which can be generally divided into high-energy and low-energy surfaces. Super-
`ficial contaminants were removed prior to each deposition by washing each substrate
`with methanol and drying in air. (U) Sebum-rich deposits: (b) eccrine-sweat-rich deposits.
`
`3.5. A model for retraction of the interfacial film
`The results of the preceding sections allow a simple model to be proposed which accounts
`for the different surface films observed with fast and slow lifting of the finger, and for
`sebum-rich or eccrine-sweat-rich deposits.
`In general the substrate surface will be inhomogeneous due to both physical irregulari-
`ties and local variations in the adsorbed film; the contact angle of the liquid film on the
`substrate will therefore vary from point to point. In static conditions the effect of a region
`of low contact angle bounded by regions of high contact angle is to produce a localized
`tail on the meniscus.
`As well as the wetting characteristics of the contaminated surface, the velocity of
`the receding meniscus will determine the nature of retraction that occurs when the finger
`is lifted from the substrate. The different character of the two deposits formed by fast
`and slow retraction is most probably a consequence of viscous effects. These are likely
`to be significant at the high rates of film retraction (about 1 m s-1) which it is possible
`to achieve under normal circumstances.
`
`

`

`720
`
`B Scruton, B W Robins and B H Blott
`
`If the film moves at low speed (slow lifting of the finger), so that there is negligible
`viscous resistance to flow, the geometry of the meniscus during retraction changes quasi-
`statically according to the local wetting conditions; retraction continues wherever the
`contact angle is nonzero and the sandwiched film flows into a few isolated islands prior
`to separation from the finger surface. In the final stages of retraction the thickened film
`necks to form a bridge between finger and substrate and eventually divides to leave a
`large droplet on the substrate. Such droplets can be seen in figure 7.
`In contrast, during fast lifting of the finger viscous effects predominate and retard
`the retraction of the sandwiched film. It can be seen from figure 10 that surfaces on
`which droplets are formed are those giving contact angles greater than 7". In this case
`the bulk of the sandwiched film retracts, keeping pace with the receding meniscus. How-
`ever, localized tails formed at surface irregularities are effectively pinned. The elongation
`of the stationary tails eventually causes necking along the surface with the consequent
`production of droplets (figure 5). For low contact angles (ie < 7") viscous effects do not
`allow the retraction of the trailing edge of the film to keep pace with thereceding meniscus.
`The whole length of the trailing edge becomes effectively pinned and a continuous surface
`film of liquid is left which may divide further as equilibrium is established (figures 5b
`and 6).
`
`4. Conclusions
`
`Human fingers are coated with a naturally occurring liquid film. The transfer by contact
`of part of the material to form a film on solid surfaces has been studied microscopically.
`Our observations show that a fingerprint deposit may take two forms: eccrine-sweat
`material forms droplets on all surfaces studied while sebaceous material forms continuous
`films on low-energy substrates (except PTFE). In the latter case it is concluded that the
`adsorption of a monomolecular layer plays an important part in the deposition mech-
`anism. In addition, from the observation of fast and slow lifting, a model of finger-
`print deposition is developed based on a balance between viscous and surface tension
`forces.
`We have established that fingerprint deposits can be transferred to a wide range of
`materials including PTFE. Therefore it is very unlikely that there are many surfaces which
`will not accept a print in the form of droplets, or pools, or both.
`
`Appendix
`
`Al. Eccrine sweat
`Much of the early work on the composition of sweat is reviewed by Kuno (1956) and
`Rothman (1954). Eccrine sweat is a dilute aqueous solution containing less than 1 % of
`dissolved solids of which inorganic salts constitute about one half. Sodium and chloride,
`in approximately equimolar proportions, are the most abundant ions; published con-
`centrations vary but a representative value (Kuno 1956) is 90 mM. Potassium (5 mM),
`magnesium (0.4 mM), calcium (0.5 mM), sulphate (0.4 mM) and phosphate are present
`together with traces of iron (Coltman and Rowe 1966), copper, manganese, iodide,
`bromide and fluoride.
`A number of nitrogen compounds occur in sweat, the major ones being ammonia,
`urea and amino-acids. On the skin surface bacterial decomposition of the urea increases
`
`

`

`The deposition of jhgerprint plms
`
`72 1
`
`the ammonia content. For fresh sweat Morimoto and Johnson (1967) gave the con-
`centration of ammonia as 3.1 mM and of urea 10.4 mM; the amino-acids serine, alanine
`and glycine were all found to be present in concentrations exceeding 0.4 mM though
`other authors differ on the relative abundances of the 21 amino-acids identified in sweat
`(Hungerland and Liappis 1972). Other nitrogen compounds occurring in smaller
`concentrations are uric acid, creatinine, creatine and choline.
`Excretion of glucose via the sweat glands is low, its concentration in sweat being
`typically only 0.1 mM. Lactic acid occurs to the extent of 4.0 mM, while pyruvic acid
`is present to a much smaller degree. Traces of water-soluble vitamins, hormones and
`drugs are known to occur. In addition the sweat may contain in excess of 1 mM of
`carbon dioxide, the concentration increasing with profuse sweating. Peter et a1 (1970a)
`report also the occurrence in sweat of small quantities of fatty acids.
`The concentrations of most of the constituents of sweat show great variation. The
`chloride concentration in the sweat of different subjects was found in one investigation
`(Coltman and Atwcll 1966) to vary in the range of 6.7-75.2 mM. The concentration has
`also been found to increase with sweating rate, (Dill et a1 1966), skin temperature and
`dietary intake of salt, and to be influenced by seasonal changes and age (Ohara 1966).
`In contrast the concentrations of amino-acids and urea are reduced during profuse
`sweating. Several components are reported to suffer a dramatic decrease in concentration
`shortly after the commencement of visible sweating, though this is probably attributable
`to a deposit already present in the sweat gland being washed out in the initial stages of
`sweating.
`Under normal conditions water is rapidly lost from the secreted sweat by evaporation
`and the concentrated material migrates from the sweat glands over the skin surface.
`However, the composition of the surface film is further modified by material from two
`other sources: the cornified (or hardened) surface layer (stratum corneum) of the skin on
`the finger tips and the surface films covering other areas of the body, especially the face
`and hair, which are touched occasionally by the fingers.
`
`A2. Stratum corneum
`
`The continuous disintegration of cornified epidermal cells at the surface of the stratum
`corneum releases the cell contents, which include the by-products of keratinization, on
`to the skin. Among the materials appearing in this way are cholesterol, cholesterol
`esters, free fatty acids, wax esters, phospholipids, squalene, amino-acids and choline
`(Rothman 1954). The proportions of the various lipid constituents of the stratum
`corneum have been investigated by Reinertson and Wheatley (1959). The presence of
`calcium and iron compounds on the skin is also due chiefly to cell disintegration (Rothman
`1954).
`
`A. 3. Apocrine and sebaceous glands
`
`Two other kinds of organ secrete on to the skin in addition to the eccrine-sweat glands
`discussed above. The sebaceous glands open on to hair follicles wherever these occur on
`the body. Apocrine-sweat glands open on to the follicles above the sebaceous glands but
`only over a few localized areas of the body. The secretion of apocrine glands differs
`from that of the eccrine glands in that it consists largely of the contents of secretory
`
`

`

`722
`
`B Scruton, B W Robins and B H Blott
`
`cells. It is a milky fluid, microanalysis of which has revealed the presence of protein,
`reducing sugar, ferric iron and ammonia (Hurley and Shelley 1960). On the face only
`the eyelids have apocrine glands. Contact of the fingers with the face and hair is likely,
`therefore, to transfer appreciable quantities of sebum but a relatively small quantity of
`apocrine sweat.
`Sebum is produced by complete disintegration of the glandular cells. It is a viscous
`liquid which spreads along the follicular canal and over the skin. Analysis by Kellum
`(1967) of pure sebum from isolated glands revealed the presence of squalene, wax esters
`and triglycerides. Free fatty acids are absent but subsequently occur in the material
`secreted on to the skin as a result of enzymatic decomposition of triglycerides to mono-
`glycerides and diglycerides in the sebaceous ducts and on the skin (Ebling 1970); skin
`surface fat may contain as much as 30% of free fatty acids. Peter et al(197Ob) found in
`sebum saturated, unsaturated and branched acids of which a high proportion consisted
`of c16 (palmitic) and c18 (isostearic, oleic etc) acids though shorter chain molecules also
`occurred. Acids esterified as triglycerides showed a similar distribution of chain lengths
`while in the wax esters acids of longer chain length were also present.
`Clearly in finger surface films the relative abundance of the materials from the various
`sources is variable. A typical rate of eccrine sweating is 2.3 kg per day (Kuno 1956);
`assuming a solute concentration of 1 % this is equivalent to the accumulation each hour
`over a 2 m2 body surface of a film of thickness 0-5 pm; even with regular washing of the
`hands films up to a few micrometres thickness will occur. Sebum may accumulate to a
`similar extent, though the contribution of apocrine sweat is probably small. The palms
`of the hands suffer a daily loss of skin of 3.5 g m-2 (a thickness of about 3 pm) by des-
`quamation (Montagna and Lobitz 1964); the quantity of material from this source
`contributing to the skin surface film is therefore likely to be somewhat less than that
`originating from eccrine sweat.
`
`Acknowledgments
`
`The authors wish to thank PSDB, Home Office, for financial support for this project.
`They also wish to thank Mr G Phillips and Professor E W Lee, for their continued
`encouragement.
`
`References
`
`Adamson A W 1960 Physical Chemistry of Surfaces (New York: Interscience)
`Bridges BC 1942 Practical Fingerprinting (New York: Funk and Wagnalls)
`Coltman C A (Jr) and Atwell R J 1966 Am. Rev. Respirat. Diseases 93 62-9
`Coltman CA (Jr) and Rowe N J 1966 Am. J. Clin. Nutr. 18 270-4
`Dill DB, Hall F G and van Beaumont W 1966 J. Appl. Physiol. 21 99-106
`Ebling F J G 1970 An Introduction to the Biology ofthe Skin ed R H Champion et a1 (Oxford: Blackwell)
`Fort T (Jr) and Patterson H T 1963 J. Colloid. Sci. 18 217-22
`Hungerland H and Liappis N 1972 Klin. Wochenschr. 50 973-6
`Hurley H J and Shelley WB 1960 The Human Aprocrine Sweat Gland in Health and Diseases (Springfield,
`Ill. : Thomas)
`Kellum R E 1967 Archs. Derm. 95 218-20
`Kuno Y 1956 Human Respiration (Springfield, 111.: Thomas)
`Moenssens A A 1971 Fingerprint Techniques (New York: Chilton)
`Montagna W and Lobitz WC (Jr) 1964 The Epidermis (New York: Academic Press)
`
`

`

`The deposition offingerprint films
`
`723
`
`Morimoto T and Johnson R E 1967 Nature, Lond. 216 813-4
`Moss A R L and Blott BH 1969 Surface Sci. 17 240-61
`Ohara K 1966 Japan J. Physiol. 16 274-90
`Peter G, Schroepl F, Fersel H G and Thurant W 1970a Arch. Klin. Exp. Dermatol. 238 154-9
`Peter G, Schroepl F, Lippross R and Weiss G 1970b Arch. Klin. Exp. Dermatol. 239 12-21
`Reinertson R P and Wheatley V R 1959 J. Invest. Dermatol. 32 49-59
`Rothman S 1954 Physiology and Biochemistry of the Skin (Chicago: Chicago UP)
`Scruton B and Blott BH 1973 J. Phys. E: Sci. Znstruni 6 472-4
`Thomas G L and Reynoldson T E 1975 J. Phys. D: Appl. Phys. 8 724-9
`Zisman W A 1964 Contact Angle, Wettability and Adhesion, ed R F Gould (Washington: American
`Chemical Society) pp 1-51
`
`

`

`J. Phys. D: Appl. Phys., Vol. 8, 1975-B Scrritou, I3 W Rol>im orrd R H Blott (see pp 714-23)
`
`Figure 2. Scanning clcctron micrograph of an area of iincoated fingerprint ridge in the
`region of an eccrine sweat pore illustrating the rough nature of a finger ridge (Magni-
`fication x 200, reduced by x l in printing.)
`
`Figure 3. Supcrpositioii of liqiiid lilnis from a normal finger at the contact between a
`finger ridge and a glass surfacc; undcr an applied load of 0.5 N (darker outlined area)
`and after increasing the load to IO N (lighter background).
`(Magnification x 250,
`reduced by x 1 in printing.)
`
`Figure4. Supcrposition 01' liquid lilnis from an acetone-dried finger at the contact between
`a finger ridge and a glass surface; under a load of 0.5 N (darker outlined area) and
`after increasing the load to IO N (lighter background) demonstrating that the areas of
`original contact are unchanged. (Magnification x 250, reduced by x C in printing.)
`
`

`

`J. Phys. D: Appl. Phys., Vol. 8, 1975-h'
`
`.Scw/on, B IY Robins mid h' H Blot, (see pp 714-23)
`
`Figure 5. (cl) Deposit remaining on a glass substrate after a contacting finger has been
`figure 3. A portion of a single ridge is shown by
`lifted (fast lifting-0.1-1 m s-l)-cf
`reflected illumination. The finger print material was eccrine-sweat-rich. (Magnification
`x 250, reduced x i in printing.) (b) Sebaceous deposit remaining on a glass substrate
`after a contacting finger has been lifted (fast lifting). A portion of a single ridge is
`shown by diffuse transmitted illumination. (Magnification x400, reduced by x -! in
`printing.)
`
`Figure 6. Scbaceotis deposit reiiiaiiiing on a PMMA (Perspex) substrate after a con-
`tacting finger has been lifted (fast lilting). A portion of a single ridge is shown and
`clearly demonstrates the continuous film observed on those surfaces that have contact
`angles less than 70". Diffuse transmitted illumination was used. (Magnification x 400,
`reduced by x Q in printing.)
`
`

`

`J. Phys. D: Appl. Phys., Vol. 8, 1975-B Scrrrfon, B W Robins and B H BIoft (see pp 714-23)
`
`Figure