Oil Red O - An alternative to the original formulation of ORO (see: (226)) isproposed, in which the methanol-based solution is replaced by propylene-glycol(224). This new formulation was proved to be as efficient as the original one, but issafer, quicker, and requires fewer reagents. It however suffers from the samelimitations as the original formulation, especially on some kinds of substrates and onaged fingermarks. A sequence of treatment for porous substrates is further proposed:"IND (/HFE-7100) – ORO (/propylene-glycol) – PD" (225). The authors recommendedreducing the immersion time in the IND solution to less than 5 seconds, to avoid adetrimental effect on the lipid fraction of the secretion (which could impact thesubsequent ORO treatment). Another research aimed at studying the sensitivity ofDFO, NIN, and ORO over time, as well as the contrast of the resulting marks, fordifferent kinds of porous substrates (227). It has been shown that ORO could beapplied subsequently to the "DFO (/HFE-7100) – NIN (/HFE-7100)" sequence, whichcould result in an enhancement of the already-detected marks and detection oflatent-remaining ones (especially on kraft paper, cardboard and thermal paper). Onwhite and recycled papers, no additional marks were detected by ORO when appliedafter DFO and NIN. Finally, a luminescent alternative to the original ORO formulationhas been proposed, which could be used on wetted and dark porous substrates(226). Substrates of interest are first processed with the original ORO, andimmediately followed by the spraying of a R6G staining solution. The marks obtainedusing this procedure appear as dark ridges on a luminescent background.