Ageing of Fingermarks - Impact and Study on Fingerprint Ridge Density

Fingermarks are a crucial part of the investigation in forensic science.

The composition of the fresh and aged fingermarks greatly differs. There are different techniques discovered that have been useful in studying that composition and further differentiating between them.

It also becomes necessary to study the facts that affect the initial fingermarks and degrade them to aged ones.  The new techniques that are being developed to study the ageing process like proteomics. The spectroscopic techniques are mostly used in the research for the features of the ageing of fingermarks. 

Composition of Fingermarks

Despite having advanced analytical techniques, little knowledge is available on the composition of fingermarks, hence, making it difficult to differentiate between the initial and aged fingermarks.  Whenever the composition of the fingermark is considered, both of the compositions (initial and aged) are taken into the account. 

Differences Between Initial and Aged Fingermarks

The initial composition of fingermarks is referred to as the composition of fingermarks on the surface just after the deposition. While the aged composition is referred to as the composition of fingermarks on the surface which has been evolved over a period of time.

Initial Fingermarks

The composition of a fingermark is a secretion composed of the substances secreted majorly from three sources namely,

• Epidermis
• Glands of the dermis layer
• The extrinsic contaminants

Reportedly, physical developers are more efficient in the case of aged fingermarks rather than in initial ones. 

Aged Fingermarks

Over a period of time, fingermarks undergo modifications like all other materials or we can say over the period of time, they age. The aged fingermarks are the result of the effects of biological, physical and chemical factors on the initial fingermarks. Hence, altering the initial composition to the final composition. 

The pace by which fingermarks age may vary on the basis of the process or the pathway it is undergoing. The phenomena by which the initial composition of a fingermark alters to aged composition can be different such as degradation, metabolism, drying, polymerization, oxidation, evaporation, and migration. 

Since the fingermark residue consists of amino acids, proteins, fatty acids, squalene, cholesterol and wax esters, studying their ageing becomes really important. Fingermarks are studied as the mixtures of protein and lipids and their oxidation is considered to be the fundamental aspect in the ageing process. 

The major loss of water is seen as the effect of ageing on the eccrine fingermark residue. The fingermarks lose approximately 85% of weight during two weeks possibly due to water loss from the fingermark residue. 

The sebaceous compounds such as fatty acids, cholesterol and squalene significantly decrease over time. The significant difference in the composition of fresh and aged fingermarks is that shorter fatty acid chains are observed in old fingermarks while longer fatty acid chains are observed in fresh fingermarks.

The significant feature of aged fingermarks is their hardening. The hardening of fingermarks can be clearly observed over time. The phenomenon of hardening may occur due to the loss of moisture content. One more possible reason studied behind hardening is the conversion of unsaturated molecules to saturated molecules. These saturated molecules tend to have an ordered crystal structure which leads the older fingermarks to have a more crystalline surface.  This process causes the fingermarks to get darkened and thicken due to exposure to air and loss of moisture. This hardening and thickening results in the formation of varnish.

Other factors influencing in the variation of fingermark composition are “transfer” that is the residue transferred which further depends on the donor characteristics, the deposition conditions, and the substrate nature. 

Also, another factor which influences the composition is the “elapsed time” between the deposition of the fingermark on the surface and its discovery as the aged fingermark. 

The environmental conditions influencing the ageing of fingermarks are humidity, light exposure, temperature, dust, rain, condensation, friction, air circulation, and other contaminants. 

Aged Fingermark Enhancement Techniques

Enhancement techniques illustrate the difference in the complex nature of the composition of the initial composition and the aged composition of the fingermarks by their efficiency on them when applied.

Development Technique

There have been a lot of techniques to study different processes related to the ageing of fingermarks. Until now, it has not been possible to study the fingermarks and draw forensic timelines and other information out of them. And hence assessing the age of the fingermark is not possible.

Spectroscopic Techniques

These are an asset in the research of ageing and dating of fingermarks. They allow the analysis of the same fingermark in the fresh state and over the period of time that is they allow conservation of sample after the analysis unlike the other chromatographic techniques (GC/MS) where samples have to be extracted from the substrates with the help of the solvents. 

FTIR (Fourier Transform Infrared spectroscopy) combined with Raman Spectroscopy is one of the techniques used to obtain basic and fundamental information about the fingermarks’ initial composition and the kinetics of the ageing of fingermarks. ATR (Attenuated Total Reflection) and single-point reflection, are both modes that can be used to study but ATR has proved to be a suitable option for the same.

ATR yields better-resolved spectra for the analysis of the effects of substrates on ageing. The spectral regions of eccrine and sebaceous materials in the initial and aged fingermarks can be studied. The spectral regions 1000-1850 cm and 2700-3600 cm are said to be most informative regarding the compositions of fingermarks. 

Proteomics

It is another technique to study the ageing of fingermarks. Proteomics is the large-scale study of proteins (Pandey and Mann, 2000).

As the substrates deposit on the fingermarks, their tendency to get altered from the original one increases which mean the protein concentration also changes most likely.

Hence, these biomolecules become the precursor to assessing the information about the ageing of fingermarks and their composition. This becomes crucial for crime investigation as these protein molecules act as target substances.  For this purpose, a screening is done based on the fluorescence.

The screening of proteinaceous material is done in parallel with the lipids. This technique helps in knowing the damage that has been caused to protein upon ageing and is also used to study the donor contact study which is the contact of donor with body fluids in forensic scenarios.

After the deposition, the fingermark residue also sees the biochemical activity that is the keratinocyte differentiation Albumins have been containing the regions which are mostly functioning as antioxidants.

One of the proteins named as DCD (Dermcidin) is mostly known for its major role in the defence of the skin. As the process of ageing proceeds, the peptide signals released by different proteins increase relatively. 

Conclusion

The ageing process of the fingermarks is mainly due to the phenomena like degradation, metabolism, drying, evaporation, migration, oxidation or polymerization.

This also changes the composition of fingermarks due to the deposition of substrates or the influence of environmental factors like humidity, light conditions, temperature, storage conditions, dust, rain, friction, etc.

As these factors act upon the fingermarks, the initial composition changes to the aged composition. The physical developer is more effective on aged fingermarks than in fresh fingermarks.

The techniques developed for the study have been useful so far. But, as the crimes have been increasing, further development of techniques is needed to study well on the fingermarks. The investigation requires the study of all the fundamental components of the fingermarks. 

Ageing of fingermarks is a complex process involving the different aspects affecting the ageing process. The deposition and adverse effects of the external factors convert the initial fingermarks into aged fingermarks.