Thursday, December 12, 2019

Application of Ultra Violet (UV) Radiations in Questioned Document Examination


Dr. Bhoopesh Kumar Sharma
Forensic Expert & Associate Professor

The questioned documents can consist of identification of fake or genuine cards, contracts, statements, titles and deeds, certificates, stamps, bank checks, handwritten letters, machine-generated documents (such as photocopiers, fax machines and printers), currency and electronic documents.

Out of all light sources, UV and IR are the significant sources of radiation that are widely used in the majority of the Questioned Document examination.

Ultraviolet (UV) is a 10 nm to 400 nm wavelength electromagnetic radiation that is shorter than visible light but longer than X-rays. UV radiation is found in sunlight and contributes about 10% of the Sun's overall electromagnetic radiation production. It is also generated by specialized arcs and lights such as mercury-vapor lamps, tanning lamps, and black lights.

Ultraviolet (UV) illumination techniques are used for multiple purposes in forensic investigations, including authenticating paintings, authenticating signatures, examining the documents in question, ink examination, highlighting latent fingerprints in crime scenes and tracing traces on clothes, detecting ink stains and identifying residual body fluid stains.

In QD examination, there're several types of applications of UV rays. Some are listed below:

1. Paper Examination: UV rays can be used to distinguish between various types of paper and paper textures. When subjected to UV, differently manufactured papers give distinguished fluorescence under UV rays. This is mainly because of the sizing (glazing) of the paper, for example, in some cases, it can appear greenish, and in others, it can be reddish. This is used to differentiate two different types of papers, even having the same experience.

2. Counterfeiting/ Counterfeited Currency or Others: Fake currency notes, security papers, passports, certificates, etc. will give different fluorescent due to the difference in sizing and the fibers present in the documents. Also, specific watermarks (Chemical and Mechanical) can be easily differentiated based on their luminescence under UV rays. Many of these government documents are embedded with multicolor security fibers that glow up in UV rays as red, green, and blue color. However, in fake documents, this will not be the case.

watermarks on bank cheque
A picture showing the presence of water marks on a bank cheque.

Chemical Water-marks as seen under UV light

A picture of a credit card showing fluorescent under UV light.

3. Examination of Alterations in Documents: Usually the spots visible under UV light, may have been treated with any type of ink eradicator. Also, the eruption of the fibers during mechanically erasing of the matter can be evidently visible under UV radiations.

4. Examination of Secret Writings: The secret writing can be made using biological fluids like urine, milk, saliva, semen, vegetable and plant juices, lemon juice, onion juice, quinine hydrochloride, and so on. Since all of these substances produce specific fluorescent under UV light, hence can be deciphered (visualized) and make the matter visible.

Secret Writing

5. Resealed Envelops: An envelop that has been opened and resealed with any type of glue may fluoresce differently under UV light.

6. Paintings Examination: Fraudulently created paintings to showcase them as the genuine work of old times, can be detected by fluorescence test. Usually, varnishes used on an old painting will fluoresce differently from modern varnishes. Other alterations to an original painting can also be detected under UV radiations. 

There can be several other cases of tampered documents, ink analysis, stamp analysis that can be easily performed using UV radiations.

In next section we will discuss the use of Infra-red radiations in the examination of Questioned Documents.


Dr. Bhoopesh Kumar Sharma
Forensic Expert and Associate Professor


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