Physical Developer (PD)
Definition
A multi-bath silver-deposition wet-chemistry method that deposits silver metal onto fatty latent print residue on porous surfaces; the only technique that recovers prints from water-soaked paper after amino acids have been washed away.
- Method type
- Multi-bath silver-deposition wet chemistry
- Targets
- Fatty latent print residue
- Surface type
- Porous surfaces
- Key advantage
- Works after water has washed away amino acids
Common questions
Why would an examiner use physical developer instead of ninhydrin on porous evidence?+
Ninhydrin reacts with amino acids in print residue, which dissolve and wash out of paper that has been soaked in water. Physical developer instead targets the fatty and lipid components of the residue, which survive water exposure, so it can recover prints that ninhydrin can no longer detect.
Why is physical developer typically applied last in a sequential processing scheme?+
It is a destructive wet process that alters the surface, so it is applied only after other methods such as amino acid reagents have been exhausted, following the standard rule of moving from least destructive to most destructive technique on a given item.
Related terms
- Alpha-Amino Acids
- Molecules bearing an amine group on the carbon adjacent to the carboxyl group; the primary molecular target of ninhydrin, DFO, and indanedione...
- DFO (1,8-Diazafluoren-9-One)
- A fluorescent ninhydrin analogue used for latent fingerprint development on porous surfaces; excite at 450-470 nm (with secondary absorption extending into the...
- HFE (Hydrofluoroether)
- A class of solvents used as carriers for ninhydrin, DFO, and indanedione formulations; lower toxicity and flammability than older acetone or ethanol...
- Indanedione-Zinc
- A fluorescent amino acid reagent (indane-1,3-dione complexed with zinc chloride) that produces an orange-yellow fluorescent product; reported to be more sensitive than...
- Ninhydrin
- A chemical reagent (2,2-dihydroxyindane-1,3-dione) that reacts with alpha-amino acids in latent print residue to produce a purple-blue compound (Ruhemann's Purple); the primary...
- Ruhemann's Purple
- The purple-blue condensation product formed when ninhydrin reacts with alpha-amino acids; the visible development indicator used in latent fingerprint examination on paper...
- Sequential Processing
- The application of chemical development methods in a fixed, evidence-preserving order that maximises cumulative recovery while preventing earlier treatments from destroying the...
- Treatment Log
- The contemporaneous written record of every chemical method applied to an item of evidence, including reagent batch, examiner identity, date/time, and result;...
- Vacuum Metal Deposition (VMD)
- A technique in which gold and zinc are sequentially evaporated in a vacuum chamber; the gold deposits uniformly while zinc nucleates differentially...