Development of latent fingermarks on the surfaces of photo paper.

Photo paper is frequently encountered in forensic investigations; however, latent fingermark development remains challenging because its surface characteristics vary according to the manufacturing process and coating structure. This study investigated suitable methods for developing latent fingermarks on commercially available photo papers. Seventeen commercially available photo papers representing two manufacturing types, resin-coated papers (RCPs) and cast-coated papers (CCPs), were examined. Latent fingermarks were developed using 1,2-indanedione/zinc chloride (IND/Zn) under different heat development conditions, either alone or in combination with cyanoacrylate (CA) fuming. The results showed clear differences between RCPs and CCPs. For RCPs, the CA-masking method (CA fuming on the nonprinting surface while masking the printing surface, followed by IND/Zn treatment on the printing surface) was the most effective approach, whereas for CCPs, IND/Zn treatment alone was optimal for both surfaces, with heating at 110°C for 60 s recommended for both paper types. In contrast, IND/Zn alone was effective for both surfaces of CCPs. The proposed methods were also effective for naturally aged fingermarks. These findings provide practical guidance for selecting fingermark development procedures according to the manufacturing type and surface characteristics of photo paper.