Use of methanol or propylene glycol-based ORO formulations over PD was advocated for developing fresh (less than 1 week old) and aged (7 days old) charged and sebum-rich latent fingermarks on wet papers (Frick et al. 2012). However, the use of PD was suggested for developing older and uncharged latent fingermarks. It was observed that use of propylene glycol in ORO formulation improves the sensitivity of reagent along with the contrast and quality of developed prints in a short time of period. Propylene glycol-based ORO formulation is simple and economical to prepare than methanol-based ORO formulation. Staining involved the immersion of article in ORO (15 min), with gentle manual agitation (30 s) at the beginning of the development time (Frick et al. 2012).
Salama and co-workers observed that ORO interacts with variety of water-soluble and water-insoluble components of latent fingermark deposits (Salma et al. 2008). The quality of developed prints depends on immersion time in water and age of latent finger impression. Beaudoin reported a case in which ORO method was used to detect and develop latent fingermarks on a 21-year-old paper (Beaudoin 2011). Immediate processing of white paper with ORO was recommended to maximize the chances of success. It was observed that the quality of developed prints depends on the nature of surface (porous, semi-porous, non-porous), method applied, and time interval between deposition and processing of latent fingermarks (Boudreault and Beaudoin 2017). In addition to it, the quality of developed prints depends on the pore size of the paper which subsequently depends on the manufacturing process and chemical composition of the paper (Rawji and Beaudoin 2006). It was noted that latent fingermarks remain stable for longer period of time on semi-porous and non-porous surfaces than porous surfaces. The quality of prints developed, on white paper, with ORO method degraded with passage of time (Boudreault and Beaudoin 2017). ORO does not involve the use of alternate light source, and results will not fade after development (Rawji and Beaudoin 2006). The use of commercial available fingermark simulants (as quality control standards) was not recommended for the assessment of latent fingermarks developing reagents like PD, ORO, NIN, and 1,2-indanedione (IND) (Zadnik et al. 2013). It was observed that sebaceous-rich marks survived longer than eccrine-rich marks in field conditions than laboratory conditions. Use of field conditions to examine the longevity of submerged marks was recommended (Sutton et al. 2014). Water treatment of surface before deposition of fingermarks produced poorer results as compared to water treatment after deposition of fingermarks (Rawji and Beaudoin 2006).
ORO reagent develops optimum quality fingermarks on different varieties of papers including kraft paper and glossy and rough side of corrugated brown cardboard (Beaudoin 2004). Although the background surface in some cases was stained pink, the red-colored ridges could be easily discerned. However, the reagent failed to develop prints on non-porous items like glass. The use of ORO for developing aged prints (less than 30 days) on wet, porous surfaces including thermal paper was suggested (Honig and Yoak 2016; Rawji and Beaudoin 2007; Salma et al. 2008; Simmons et al. 2014). Latent fingermarks impinged on thermal papers, followed by immersion in water for 2 h, could be developed even after 30 days with ORO. Likewise, imprints deposited on photocopier paper, followed by soaking in water for 24 h, could be developed after a lapse of 30 days. Prints could also be developed by ORO method on unplasticized polyvinyl chloride that has remained soaked in water for week (Wood and James 2009a, 2009b).
It has been pertinent to compare the performance of ORO method with the PD technique which too develops fingermarks on dry and wet porous surfaces. Neither ORO nor PD develops fresh or aged (7 days old) latent fingermarks on paper which were submerged in petrol (Wood and James 2009a, 2009b). With ORO reagent, the calligraphic script on paper, no doubt, gets despoiled, yet the overall results were better than those obtained with PD. Further, although ORO produced better results on photocopier paper than on kraft paper, the reverse was true of PD. The use of ORO was recommended to develop latent fingermarks on moist, porous surfaces (thermal and white standard paper) after comparing it with PD method (Rawji and Beaudoin 2006).
ORO was found to be less damaging to evidence and provides better quality prints than PD (Guigui and Beaudoin 2007). Operational setup of ORO has been much less complex than PD and provides high-quality intense prints, and therefore, it could be used as an alternative to the traditional PD (Beaudoin 2004; Guigui and Beaudoin 2007; Rawji and Beaudoin 2006; Salma et al. 2008). The superiority of ORO over PD was advocated to develop fresh and aged (less than 30 days) latent fingermarks on wet, porous surfaces including white and thermal papers (Beaudoin 2011; Guigui and Beaudoin 2007; McMullen and Beaudoin 2013; Mingchao and Danhua 2015). In contrast to this, other authors observed that ORO was not an effective method for developing latent fingermarks as thermal paper loses writing or information on treating with ORO (Rawji and Beaudoin 2006).
ORO outperforms PD so long that the latent impressions were fresh or at the most 4 weeks old. For more aged impressions, PD performs better. No doubt, ORO method has a fewer steps as compared to PD technique, yet the immersion time (90 min) in the stain solution make the overall process slower. Nevertheless, ORO technique may be used after all routine amino acid-specific reagents have been tried out without success (Guigui and Beaudoin 2007; Salma et al. 2008). For fresh prints, the recommended order of sequencing was ORO, followed by PD (Guigui and Beaudoin 2007; Rawji and Beaudoin 2007).
Simmons and co-workers compared different processing methods (PD, ORO, modified PD) to develop latent fingermarks (fresh and aged) on moist porous surfaces (white paper, cardboard) (Simmons et al. 2014). Tween 20 in place of Synperonic-N in modified PD composition was used for enhancing latent fingermarks. The use of PD and modified PD over ORO for processing such types of substrates was suggested. In an another comparative study, Honig and Yoak suggested that ORO could be used as an efficient alternative to PD and NIN for enhancing latent fingermarks on dry and moist, porous surfaces as it provides intense and better quality prints than PD and NIN method (Honig and Yoak 2016).
PD was recommended over ORO to develop aged (older than 28 days) latent fingermarks on different kinds of papers (Ramotowski 2012). A number of studies have demonstrated that ORO was superior to PD; however, such studies used “loaded” sebum rich fingermarks (Salma et al. 2008; Rawji and Beaudoin 2006). In contrast, other studies using “ungroomed” fingermarks found that ORO did not outperform PD for the detection of latent fingermarks up to 7 days old (Wood and James 2009a, 2009b).
Wood and James observed that neither PD nor ORO develop quality fingermarks on card surfaces when using normal fingermarks as opposed to loaded fingermarks (Wood and James 2009a, 2009b). Less effectiveness of ORO towards old prints, insensitivity towards water-soluble components of latent fingermarks, and negligible success towards developing latent fingermarks on non-porous surfaces are some of the major drawbacks of ORO reagent method.
Sutton and co-workers recommended the use of Sudan black and gentian violet over ORO for developing fresh and aged (more than 10 days old) latent fingermarks on smooth, non-porous surfaces like glass, plastic, and metal (Sutton et al. 2014). Beaudoin suggested the use of ORO followed by rhodamine 6G for the development of fresh and aged (10 days old) latent fingermarks on dark, moist, and absorbent substrates such as black cardboard (Beaudoin 2012).
For wet, porous surfaces, the recommended sequence was ORO followed by PD while for dry, porous surfaces, the recommended sequence was DFO → NIN → ORO → PD (Beaudoin 2011). Use of sequential processing with propylene glycol-based ORO and Tween 20-based PD formulations over propylene glycol-based ORO formulation alone was advocated for developing fresh and aged latent fingermarks on white copy papers. It was observed that both methods can be used as complementary as both methods targets the different components of latent fingermarks (Frick et al. 2017). In another study, sequential processing with NIN followed by ORO was recommended to develop latent fingermarks on wet, thermal papers (McMullen and Beaudoin 2013). In a similar study, sequential processing with DFO followed by NIN followed by ORO was suggested to develop latent fingermarks on wet papers (Guigui and Beaudoin 2007; McMullen and Beaudoin 2013). PD could be successfully used after processing the items with ORO as ORO did not influence the quality of prints developed by PD (Swofford 2010). Use of PD followed by ORO was suggested for developing latent fingermarks as ORO enhances the quality of prints developed by PD (Salma et al. 2008). McMullen and Beaudoin demonstrated that the sequential processing with DFO–NIN–ORO did not prevent the development of useful fingermarks on paper and ORO developed fingermarks that had been undetected with the DFO–NIN sequence (McMullen and Beaudoin 2013). ORO enhances the quality of prints already developed with NIN and DFO. However, sequential processing with NIN and DFO after ORO reduces the contrast produced by ORO. ORO was more sensitive than NIN but less sensitive than DFO. The order in which these methods were applied was selected so that the success of each technique was not hindered by a preceding technique.
The insertion of ORO in fingerprint development sequence was advocated. The use of ORO reagent before PD was suggested as ORO treatment did not interfere in subsequent processing. The recommended sequence for processing latent fingermarks on dry paper was DFO → NIN → ORO → PD while the sequence ORO → PD was recommended for processing latent fingermarks on wet paper. ORO was less damaging to evidence and gives better quality prints than PD (Guigui and Beaudoin 2007).
The inclusion of propylene glycol-based ORO reagent method into the processing sequence after treatment with IND and followed by treatment with PD (IND → modified ORO reagent → PD) was suggested for the development of fresh latent fingermarks on wet paper as it increases the efficiency of sequence in addition to quality of developed prints and no interference was observed between these techniques, as each technique targeted a different component of latent fingermarks (Frick et al. 2013).