Problems of Forensic Sciences 2012 Vol. 92 (XCII) 311-318
VISUALISATION OF DISAPPEARING INK WRITINGS
Bikram Ashok VAID, Sanjeev KUMAR, Rajender Singh RANA, Narendra KUMAR
Central Forensic Science Laboratory, Shimla, India
Streszczenie
A new technique for committing bank frauds using disappearing inks in the execution of various bank instruments is currently very much in vogue. Such types of inks become invisible over a period of time, depending upon the constituents of the ink, and are then not normally visible under visible light or ultra-violet rays or infra-red rays, making them a very handy tool for forgers wishing to cheat society. Disappearing inks are water-based acid-base indicators (pH indicators), which change from a coloured to a colourless solution upon exposure to air. The most common pH indicator for inks is thymolphthalein (blue). This indicator is mixed with a basic solution that becomes more acidic upon exposure to air, resulting in a change of colour. Visualization of such secret writings is possible by viewing the suspect document under a spotlight, a facility available in the Video Spectral Comparator-2000 HR.
Słowa kluczowe
Disappearing ink; Acid-base indicator (pH indicator); Infrared rays; Transmitted light; Spotlight; Video Spectral Comparator-2000 HR; Ultraviolet rays; Bank instruments.