Development of a Nondestructive Technique for the Identification and Analysis of Erasable Ink
Parvesh Sharma, Kapil Kumar, Himanshu PandyaBackground:
Erasable inks, particularly thermochromic formulations such as Pilot FriXion, pose significant challenges in forensic document examination due to their ability to disappear upon heating and reappear under cold conditions. Their misuse in forgeries necessitates reliable, nondestructive analytical techniques.
Aims:
To develop and evaluate nondestructive methods for detecting, differentiating, and restoring erased erasable ink on paper substrates using VSC-based optical illumination and complementary forensic techniques.
Methods:
Simulated samples were prepared using erasable and non-erasable inks (blue and black) on standard A4 sheets. Four sample types were examined: erasable inks, erased erasable inks, overwritten samples, and regular non-erasable inks. Examinations were conducted using a calibrated VSC 6000/HS across 275 lighting conditions (400–1000 nm), including floodlight, spot fluorescence, UV illumination, and transmitted/side lighting.
Results:
Erasable inks demonstrated complete disappearance beyond 590 nm in floodlight mode, confirming thermochromic behaviour. Spot fluorescence between 645–780 nm clearly revealed erased erasable blue ink and partially revealed black ink. Overwritten samples showed complete recovery of underlying erased writing in the 645–665 nm range. UV (254–365 nm) illumination enhanced detection of erased zones, while transmitted and side lighting revealed pressure marks from erased content.
Conclusion:
VSC-based UV and spot fluorescence modes proved highly effective for nondestructive detection and recovery of erased erasable inks. Even overwritten areas revealed underlying content. These findings support the forensic applicability of VSC illumination techniques for reliable restoration and authentication of questioned documents.