Latent fingerprints developed with conventional powders have to be photographed and/or lifted on adhesive tapes to preserve the details. Various elastic and rubber lifting materials are commercially available nowadays, but are rather expensive, being mostly imported products. In the present paper the possibility of substitution of those products with domestic adhesive material, namely self-adhesive wall-paper ("Cetifix"), is described. The results yielded by our research have shown that the material we have been concerned with is not only an appropriate substitution for the imported lifting tapes, but has a number of serviceable advantages over them.
KEYWORDS: criminalistics, latent fingerprints, fingerprint preservation, lifting fingerprints
A fingerprint found at the scene of crime, or on some object related to the crime, is often the most valuable, but at the same time one of the most delicate pieces of physical evidence. That is why detection, collection and preservation of such evidence must be conducted with utmost care. There is a number of methods and procedures in that course, and new, more sophisticated techniques are continuously under development.
Generally speaking, fingerprints are formed by friction ridges which deposit perspiration, grease and dirt on the object touched. It may also happen that the fingers are contaminated with foreign colored matter, or they may press against plastic material and produce a trace visible to the naked eye. Visible fingerprints are processed without greater difficulties, as they can be easily preserved for further examination. Unfortunately, fingerprints found at the crime scenes are mostly in their invisible or latent form and must be searched for and made visible on an object which is suspected of having been handled by a person involved in crime. Latent fingerprints may be revealed and rendered permanently visible by various methods of processing, which are referred to as developing. The methods available for developing latent fingerprints are quite numerous (1,3,4). One of the oldest, most common and readily available methods used by police worldwide is that of dusting, or powdering a surface with a fine powder of contrasting color. The powdering technique is based on the simple phenomenon of mechanical adhesion of the powder to the fingerprint deposits: a suitable powder is applied to the latent fingerprint by means of a fine brush. The powder adheres to the fingerprint pattern made by sweat and grease, revealing the pattern which becomes clearly visible. There are several types of commercially available fingerprint powders: black, white, aluminium, copper, fluorescent and magnetic powders. The choice of powder depends upon the nature and color of the surface, the specific method of preservation, the external conditions and age of the print, i.e. duration of time elapsed since the print was made (2). The most frequently used powders in general purposes are aluminium fingerprint powder, which is applied by fine rabbit-hair, camel- hair or squirrel-hair brush, and magnetic powders which are applied by magnetic applicator.
It is desirable to select a powder which will produce a black print on a light background, because the comparison prints of suspects are black on white paper surface, and the matching may thus be facilitated.
Once the fingerprints are developed, they must be preserved in order to prevent accidental impairments. Photographing is by far the best and the most accurate method of preserving once developed fingerprints for further examination and presentation of fingerprint evidence in the Court of law. However, it is often desirable to transfer a fingerprint from an item upon which it is found to a medium suitable for comparison and further scrutiny. The process of fingerprint transfer is commonly called lifting and is ordinarily done for the purpose of preserving details of original print in a permanent form. Occasionally, lifting is also done in order to make a good
photograph of a print possible (3). Various lifting materials are today available in form of sheets or tapes. Lifters are mostly made of a thin rubbery or synthetic material coated with an adhesive and protected by a transparent celluloid cover. Lifters come in different sizes, forms and three colors: black, white and transparent. Process of lifting is based on physical adhesion of powder from friction ridges pattern of dusted print to the sticky surface of the lifter. In the process of lifting, the protective covering of the lifter is pulled away and the sticky surface is carefully pressed over the dusted print and then pulled away. After collecting the fingerprint, the protective covering is carefully replaced on the lifter. Once the fingerprint is transferred to a lifter, it becomes permanent and does not get smeared off or damaged by an accidental disturbance of surface bearing it.
A large majority of equipment needed for processing fingerprints is imported to our country. During the hardships of the war which has been ravaging our country for five years, we were compelled to look for suitable locally manufactured products instead of those from abroad. This research is a part of contribution of our Department (Department of Criminalistics) in that course, and represents our attempt to find an adequate substitution for costly and hardly available lifting materials.
Moreover, it is a long-term policy of the Police College to employ a good deal of our energies to educate a highly professional police force, part of which is inevitably a proper education of its technical units. We therefore tend to engage as many students as possible in the research projects of our Department, and it is important to stress at this point, that a valuable part of this research is greatly indebted to a graduation thesis of one of our students, Mr. Stjepan Pupak.
We decided to examine useful features of domestic self-adhesive wall-paper produced by "Cetinka", Trilj - commercially called "Cetifix" - as a possible substitute for the commonly used lifting tapes. We chose the wall-paper because it is a readily obtainable low-cost product that can be bought in ordinary drug-stores and elsewhere. The wall-paper is packed in 45cm wide rolls and can be easily cut out in appropriate size. It comes in a variety of different colors, which makes it particularly suitable for contrasting in cases when colored powders are used for print-development.
A series of experiments has been conducted, in which we compared the quality of prints lifted the with wall-paper and those with conventional fingerprint lifters, in order to decide whether the wall-paper has any conceivable advatnages or disadvantages over conventional fingerprint lifting materials.
Materials and methods
Black and transparent "Cetifix" self-adhesive wall-paper were selected to match the ordinary forms of lifters used in practice. Characteristics of the black wall-paper are compared with the black gelllifter (Folien-Vogel, Vienna,Cat. No. 10x), and those of transparent wall- paper with the transparent instant lifter of the same manufacturer. Those gelllifters and instant lifters are an integral part of the universal and fingerprint investigation kits, used in practice by our technical units.
Gelllifter consists of a thin sheet (13x18 cm) of tacky flexible rubber adhered on a white paper backing sheet. Adhesive film is protected with a transparent celluloid cover. The suitable size of the lifter can easily be cut out from the sheet. Black gellifter is commonly used for lifting fingerprints developed with light-colored powders. Print fixated by black lifter is a mirror-image of the original print.
Instant transparent lifter consists of a transparent adhesive film adhered to a transparent poliethylene backing and a protective transparent cover. The protective cover has a die-cut, for ease of removing. It is employed for fixating prints developed with light and dark powders, and an appropriate background is to be selected. Print preserved on the transparent lifter is a positive image of the original print.
Our "Cetifix lifter"- as the product under consideration will be referred to from now on - is a cut out strip of the "Cetifix" black or transparent self-adhesive wall-paper, and a fitting sheet of the (transparent) overhead projection film, which serves as a protection cover.
The method of lifting is simple and easy to master, although some experience is required. Appropriate size of the lifter must be cut, the protecting covering stripped from the adhesive surface and one end of the tape must be held near one side of the dusted print. The adhesive surface of the lifter is then to be rolled slowly over the print. Care must be taken to prevent any bubbles or bulgings filled with air. The tape is then to be pulled away and the protective covering must carefully be placed, avoiding air bubbles and bulgings again.
The method of lifting fingerprints with "Cetifix lifter" is rather similar. The appropriate size of the wall-paper is cut, protecting paper is stripped off, and the adhesive surface is rolled over the dusted print taking care to avoid producing air pockets. The tape is than pulled away and the fingerprint pattern is protected by the cover of a projection film sheet. At the back-side of the lifted print a note with specific details can be attached.
Experimental procedures and experimental results
The experimental program was designed to determine the following:
The procedure used in all experiments was the same: sets of latent fingerprints of normal (uncontaminated) eccrine gland secretions were placed on various surfaces. Smooth non-porous surfaces were used, the kind from which powdered fingerprints are usually preserved by lifting process. The figerprints, left to age for one hour, were developed using conventional powdering techniques. For testing black lifting tapes silver aluminum fingerprint powder (silver aluminum powder, Folien-Vogel, Cat. No. 31) or other light colored powders were used for developing, while for testing the transparent lifters dark magnetic powder (Magna Powder, Yet black, Folien-Vogel, Cat. No. 57) was used.
Characteristics of "cetifix lifters" were compared to those of conventionaly used lifters in
such a way that a half of the dusted fingerprint was fixed on "cetifix lifter", while the other half
was fixed on coneventional lifting tape. Photographs were made
Set of experiments #1
In order to determine whether prints of quality equal to the standard lifters can also be
attained by "Cetifix lifter", two pairs of latent fingerprints were left on a white ceramic plate
and on a plain glass plate. After ageing one hour, one pair of fingerprints on each of those
surfaces was developed with aluminum powder and subsequently lifted by black "Cetifix" and
black gelllifer. The results obtained are illustrated by photographs shown in Fig. 1 and 1a for
the ceramic plate, and in Fig. 2 and 2a for the glass plate.
(Refer to Figures 1, 1a, 2 and 2a)
Another pair of latent fingerprints on both plates was developed with magnetic powder
and subsequently lifted with transparent lifters (a half of print with "Cetifix" and another half
with standard transparent lifter). The results obtained are illustrated by photographs shown in
Fig. 3 an 3a for the ceramic plate, and in Fig. 4 and 4a for the glass plate.
(Refer to Figures 3, 3a, 4 and 4a)
It can be seen that halfs of fingerprints preserved on "Cetifix lifters" are all of high quality, with excellent clarity and fully visible details of friction ridges are obtained. The distinctness and clarity of ridge patterns is higher on "Cetifix lifter", compared to commonly used lifters.
Set of experiments #2
To examine the influence of different fingerprint powders on applicability of "cetifix lifters", various fingerprint powders other than aluminum and magnetic were applied for developing fingerprints from smooth non-porous surfaces.
Some of the Folien-Vogel's fingerprint powders, which are constituents of investigation
and fingerprint kits, namely Dragon Blood (Cat. No. 41), Velvet Gray (Cat. No. 22),
Ferropodium (Cat. No. 38) and various fluorescent powders were used for developing latent
fingerprints placed on a glass plate and subsequently lifted with "cetifix" and with standard
lifters. Again, one half of developed fingerprint was lifted with "cetifix lifter", and the other half
with standard lifter, black or white, with respect to the powder used. Experimental results
showed no noticeble differences in adhesive properties of "cetifix" and standard lifters with
regard to various kinds of fingerprint powders, as can be illustrated by photographs in Fig. 5. for
some representative examples.
(Refer to Figure 5)
On the basis of this set of experiments, it can be concluded that "cetifix" has almost the same affinity towards all of the powders here tested. Due to higher adhesivity, "cetifix" adheres considerably more powder than gellifter.
Set of experiments #3
The following set of experiments was conducted with intention to elucidate weather the
nature of the surface from which latent fingerprint has to be preserved has any influence on the
quality of prints preserved on "Cetifix lifter". The type of surface was chosen to match those
surfaces from which powdered prints are mostly preserved in practice by lifting procedure. The
results of the first set of experimens have already shown that fingerprints of excellent quality
can be obtained from smooth flat non-porous surfaces such as cermic plate and glass. In
followig experiments latent fingerprints were deposited on a shiny plastic black colored powder
box and on a wallet made of smooth brown leather. Fingerprints were developed with
aluminum powder, and lifted partly by black "Cetifix"and partly by black gellifter. The results
obtained, illustrated by photographs in Fig. 6 and 6a for the powder box, and in Fig.7 and 7a for
the leather wallet, revealed that the high quality fingerprints were obtained on both of the two
tested surfaces.The fingerprints fixed on "Cetifix lifter" are more clearly visible, due to greater
adhesivity in comparison with common lifters.
(Refer to Figures 6, 6a, 7 and 7a)
Set of experiments #4
Next, the experiments were conducted to compare applicability of "Cetifix" and common
lifters in lifting fingerprints from curved surfaces. Fingerprints left on a coffee cup, a laboratory
glass and a holder of a kitchen knife were developed with appropriate powders (aluminum
powder was used for the coffee cup and for the knife, black magnetic powder was used for the
glass) and photographed.
(Refer to Figures 8, 9 and 10)
The fingerprints were then partly lifted with "Cetifix lifters", and partly with standard lifters (Refer to Figures 8a, 9a and 10a).
Concerning the practical applicability, "Cetifix", as a thinner and more flexible material, is quite easier to handle and has better adaptibility to courvatures.
Set of experiments #5
The permanence of fingerprints preserved by lifting process with "Cetifix lifters" is
compared to those preserved with conventional lifters was examined. Pairs of powdered
fingerprints were lifted on black "Cetifix lifters" and black gellifters and left to age under
normal indoor conditions (room temperature, normal humiditylevel). After preserving lifted
fingerprints for about a year, no apparent change in the quality of the ridges or their permanence
was found. After one year, however, it appeared that the protective covering from gellifter
started to detach along the edges, while the transparent projection film of "Cetifix lifter" was
still firmly and uniformly adhered to the surface.
(Refer to Figure 11. and 12)
The present study demonstrates that "Cetifix lifter" can render fingerprints of excellent quality left on hard, smooth non-porous surfaces. Compared to commonly used lifters, friction ridges preserved on "Cetifix" are more distinct and clear. This fact should be explained by better adhesivity of self-adhesive wall-paper. (In our research we used only "Cetifix" wall- paper, but it is probable that self-adhesive wall-papers of other manufacturers produce the same effects). More powder from dusted ridge pattern is transferred by higher adhesivity, which is the key reason for the successful results produced by "Cetifix lifter".
Furthermore, "Cetifix lifter" can be used for lifting fingerprints developed with all kinds of powders, and compared to commonly used lifters, preserved prints will be of higher quality, owing to higher adhesivity of the wall-paper.
"Cetifix lifter" can be used for lifting dusted fingerprints from all kinds of smooth or polished articles - all the surfaces from which conventional lifters are used. However, due to such good affinity towards powder, lifting procedure cannot be repeated with "Cetifix"as is the case of gellifters or synthetic lifting tapes.
Due to its thinness and higher flexibility, "Cetifix lifter" is more suitable for lifting fingerprints from curved smooth non-porous surfaces.
Finally, "Cetifix lifter" posseses the following advantages: flexibility, softness, resistance to wearing off and aging. It is known from practice that gelllifters, soon after opening their pack, loose elasticity and adhesivity, and become insuitable for use. Owing to stability and permanence of the wall-paper, prints preserved on them are longlasting.
The proposed technique of lifting fingerprints with "Cetifix lifters" prooved to be simple, not requiring excessive handling, expeditious and convenient.
One of the advantages of the self-adhesive wall-paper is that it comes in many different colors, and one can pick the most suitable background color to bring about the best color contrast, when colored powders are used for the developing.
The mayor advantage, however, of the "Cetifix lifter" happens to be of economic nature. We compared cost estimates for domestic products and retail price and standard imported products at their imported prices. According to our figures, the "Cetifix lifter" is about five times cheaper than commercialy available imported lifters, and that fact should not be easily disregarded.
The method of lifting dusted fingerprints with the "Cetifix lifter" has been found very convenient and reliable for preserving fingerprints on smooth and non-porous objects, regardless of the powder used for the developing.
Compared to the commercialy produced imported lifting products, the "Cetifix lifter" has several advantages which must be taken to account. First of all, it has superior physical qualities, such as higher adhesivity, elasticity and durability. It is also rather convenient for handling and utilization, and last but not least - it is of considerably lower cost.
The autors gratefully acknowledge Mrs. Marija Celesnik, Photography Division, Criminal Investigation Department of Ministry of the Interior, for her support in preparing photographs.
Appreciation is also expressed to Mr. Pavel Gregoric for his valuable help in translating the manuscript.
The HTML conversion of this chapter was supported by the
National Institute of Justice/
National Criminal Justice Reference Service