Dynamics of latent fingerprints: The effect of physical factors on quality of ninhydrin developed prints – A preliminary study Om Prakash Jasuja, M.A. Toofany, Gagandeep Singh, G.S. Sodhi พ. ต. ท. ธนบูรณ์ ธัชศฤงคารสกุล รหัส ดร. ศิริรัตน์ ชูสกุลเกรียง อ. ที่ปรึกษา

The objective The effect of some of exudation of sweat, the type of surface on which latents are deposited, the ability of the donor to deposit fingerprints, contact time, force of contact and their effect on the ability of ninhydrin (1% ninhydrin solution) to develop the marks. Latent fingerprints from good and bad donors were obtained on paper with variable pressure under controlled conditions.

The previous work - Thomas [1] studied various physical parameters of fingerprints such as their formation, droplet properties, contact angles, optical properties and electrical properties. - Jones et al. [5] discussed a large number of factors including donor variations, which may affect the development of latent fingerprints and can play a vital role while formulating and evaluating a fingerprint development reagent.

Overview - Introduction - Fingerprint - ninhydrins - Experiment - Results and discussion - Conclusion

Fingerprints

Ninhydrin Molecular formula C9H6O4C9H6O4 Molar mass g mol −1 Density0.862 g/cm 3 Melting point 250 °C, 523 K, 482 °F Chemiscal Properties Formular compound

2.1. Control of pressure 2.2. Control of exudation of sweat 2.3. prepared ninhydrin 2.4. The quality of developed fingerprints

study as follows 1.consisted of twenty individuals. 2.consisted of five individuals considered to be good sweat donors. 3. consisted of five individuals considered to be bad sweat donors.

touched finger of the donor on the paper with placed on a flat pan of a balance. deposited at pressure equivalent to 50 g, 100 g 150 g and 200 g Control of pressure

2.2. Control of exudation of sweat taken off the hands and the index finger was pressed on the paper as mentioned above. covering the donors hand loosely with a polythene bag for various time periods ranging from 30–180 s. stored latent fingerprint sample in paper envelopes.

dissolved 1.0 g of Ninhydrin in acetone and added 2 drops of acetic acid make volume to 100 mL with acetone 2.3 Ninhydrin was used as the developing reagent and was prepared as follows stored in the refrigerator and come to room temperature half an hour before use.

latent fingerprints immersed ninhydrin solution. dried dry in the open air for a few minutes before being placed in an oven maintained at 100 °C for approximately 2 min. kept ninhydrin solution between 30 and 35 °C and humidity at 55–65%.

2.4. The quality of developed fingerprints was graded as follows Fig. 1. Fingerprint depicting poor quality (Grade 2). Fig. 2. Fingerprint depicting medium quality (Grade 3).

Fig. 3. Fingerprint depicting good quality (Grade 4). Fig. 4. Fingerprint depicting excellent quality (Grade 5).

Figur e no. Induced sweating time (IST) (s) Pressu re (g) Qualit y 13050Weak Mediu m Good Excell ent Table 1 Effect of Physical Factors on the quality of latent fingerprints development

Fig. 5. Pressure vs quality at different induced sweating time (IST) n=20 (mixed population).

Fig. 6. Pressure vs quality at different induced sweating time (IST) in rich donors n=5.

Fig. 7. Pressure vs quality at different induced sweating time (IST) in poor donors n=5.

a linear effect of force applied to deposit fingerprints and the sweating characteristics of a donorcould be established with respect to the quality of the developed prints, but in case of good donors smudging of fingerprints took place when the pressure applied and induced sweating time exceeded 200 g and 180 s respectively. 120 s of induced sweating time produced the same quality of development of the donated fingerprints irrespective of the donor.