Latent Print Development
Latent Print Development
This domain tests whether you can choose and sequence latent print development methods for porous, non-porous, adhesive, wet, and blood-bearing surfaces. The exam favors reagent specificity, sequence logic, and documentation over reagent recipes.
Core rules
- Porous surfaces (paper, cardboard, untreated wood): amino-acid reagents-DFO, ninhydrin, 1,2-IND-then physical developer (PD) for aged, wet, or previously processed items. DFO is generally used before ninhydrin because it is more sensitive and fluoresces.
- Non-porous surfaces (glass, metal, plastic): optical and oblique lighting first, then powders, cyanoacrylate (CA) fuming, fluorescent dye stains (rhodamine 6G, basic yellow 40, ardrox), and vacuum metal deposition (VMD) as a later option.
- Blood: luminol is presumptive and useful on cleaned or dark surfaces; enhancement reagents include amido black, leuco crystal violet, acid yellow 7, and DAB. Blood enhancement is not DNA analysis.
- Sequence: least destructive to most destructive; document before and after; record reagent lot, date, and examiner.
Worked example A dry glass bottle is submitted. Start with visual and oblique lighting, then powder (black or magnetic) because it is relatively non-destructive and reversible. If powder fails, CA fume the bottle, then apply a fluorescent dye and examine under appropriate excitation. VMD is reserved for later because it is less reversible. On a paper envelope, by contrast, powder is inappropriate; use DFO, then ninhydrin, then PD if the paper is wet or aged.
Traps
- Powders on wet or greasy items.
- Ninhydrin before DFO on porous items.
- Treating luminol as confirmatory.
- CA fuming before powder when powder would suffice.
- Forgetting reagent lot and date and pre/post photographs.