Oil Red O—For Developing Latent Prints on Wet Paper
Sounds like a weird name for a latent print development reagent, but this chemical is finding its way into crime labs throughout the world. Amino acids dissolve in water, and, therefore, fingerprints on porous surfaces that have been exposed to moisture (water) usually do not respond well with traditional methods of latent development chemicals like ninhydrin or DFO. A longtime favorite, the Physical Developer (PD) method, is most often used.
In 2004, Alex Beaudoin, Services de l’Identité Judiciaire at the Sûreté du Québec, developed a method that made the recovery of fingerprints on wet porous surfaces simple and easy. Specifically, surfaces such as paper and cardboard that had been exposed to water or high humidity were ideal for Oil Red O (ORO). His three-step method displayed simplicity and differed from the multistep PD used in laboratories across Quebec
Beaudoin conducted tests to compare Oil Red O and physical developer on three types of paper surfaces: thermal paper, white standard paper, and brown kraft paper. Oil Red O was consistently superior to physical developer in terms of the mean fingerprint quality produced on thermal paper. Oil Red O was also shown to be superior for recovering fingerprints on standard white paper. On brown paper, the fingerprint quality was not significantly different between the two methods. This research supports the use of Oil Red O in laboratories for the treatment of wet porous surfaces. And Oil Red O is far less expensive and a lot less complicated to use.
Formula preparation:
1.54 g Oil Red O powder dissolved in 770 ml Methanol
9.2 g Sodium hydroxide dissolved in 230 ml distilled water
Add the Sodium hydroxide solution to the Oil Red O solution.
Mix & filter the combined solutions. Store in a dark bottle.
Safety Caution: Methanol (wood alcohol) is highly flammable and toxic. Wear safety goggles, latex gloves and an organic vapor respirator when mising and using this substance. Use only with adequate ventilation or exhaust hood.
Procedure:
1. Immerse the item in stain solution and soak completely. It is optional to agitate the solution on a
shaker platform.
- Ridge detail should begin to develop in 5 min.
- Weak fingerprints (poor lipidic content) may require 60 to 90 minutes of development time.
2. Remove & drain item - immerse in a pH7 buffer solution.
3. Remove item from buffer solution - rinse in distilled water.
4. Dry item at room temperature - or heat in an oven at 50 degrees C (122 degrees F).
Learn more about chemical development methods from the Technical Bulletin: “Overview of Latent Print Development Techniques”
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