Ultraviolet (UV) illumination techniques are used for multiple purposes in forensic science examinations. It includes; Duplicate Paintings, Forged Signatures, documents in question, ink examination, latent fingerprints examination, detecting ink stains and identifying trace of body fluid at crime scene or on clothes.
The Questioned Documents can consist of identification of any type of fake or genuine documents, such as; stamps, will, sale deed, bank checks, handwritten letters, printed documents and digital documents, etc.
Detection of forgeries in documents under long and short wave ultraviolet light usually examine several Documents in question.
UV is the significant sources of radiation which is widely used in Questioned Document examination. It is also generated by specialized arcs and lights such as mercury-vapor lamps, tanning lamps, and black lights.
Ultraviolet light also known as ultraviolet radiation is a form of energy which is a part of the electromagnetic spectrum. Ultraviolet (UV) is a 10 nm to 400 nm wavelength electromagnetic radiation that is shorter than visible light but longer than X-rays(visible light ranges from 400 nm to 700 nm, and infrared light ranges from 700 nm to 1200 nm).
Ultraviolet radiation is produced by natural sources, such as; the sun (It contributes about 10% of the Sun’s overall electromagnetic radiation production) and artificial ones, such as black light tubes, mercury vapor lambs, and electronic flashes, and it is often accompanied by visible light.
The ultraviolet portion of the spectrum has been divided into three regions:
1. Short wavelength: It ranges from 180 to 280 nm. It is used in Following work: Sterilisation, Chromatography, Mineralogy and Photochemical reactions, etc.
2. Medium wavelength: It ranges from 280 nm to 320 nm. For Medium wave transmission of UV a quartz lens is required. Sun lamps are artificial sources for this type of radiation and it is used for cosmetic and therapeutic purposes;
3. Long wavelength: It ranges from 320 nm to 400 nm and also known as near ultraviolet. This UV region is produced by portable lamps and can be very beneficial to the forensic experts for document examinations.
UV radiation is used for many types of Suspected Document examination, Some are listed below:
1.In examination of Paper: Differently manufactured papers give different fluorescence under UV rays. UV rays are very much beneficial to recognize the different materials of paper by producing various fluorescence for example, it may appear greenish in some cases while it can be reddish in other cases.
2. In examination of Inks: Fountain pen inks of different brands have different composition in addition to their similar colors when examined under UV light.
3. In Examination of Counterfeited Document: UV radiation will give different fluorescence with different sizing and fibers present in the document. authentic documents use different types of sizing, inks, different colors of fibers, Specific watermarks (Chemical and Mechanical), and papers, etc. in printing while duplicators can’t use the same source so these minute details can be detected by UV light. Generally, Following types of documents are prepare in duplicate: Fake currency notes, security papers, passports, certificates, etc.
4. In Examination of Alterations in Documents: If document has been treated with anytype of chemical eraser or mechanical eraser then spots will be visible under UV light.
5. In Examination of Secret Writings: The secret writing can be made using biological fluids like urine, milk, saliva, semen, vegetable and plant juices, and quinine hydrochloride, etc. All of these produce specific fluorescent under UV light, Which makes it easier for expert to decipher that hidden content.
6. In examination of Resealed Envelope: An envelope that is opened and re-sealed with any type of glue can fluorescent differently under UV light.
7. In examination of duplicate or forge Paintings: Forgers always try to make duplicate copy of famous paintings and try to showcase them as original work. These type of forgery are easy to detect with the help of UV light. different paint colors give different fluorescent, specially paints used on an old painting will fluoresce differently than modern. 2nd important thing is to detect the paper of painting, aging of paper can easily examined under UV light radiation.
8. In Examination of Stamp, Bank notes, Credit cards,etc.: With the help of UV light many more document forgeries can be determine.