Several very effective methods are available for latent print development on porous materials. Iodine fuming was discussed in PrinTips-02. This article will cover DFO (1,8-Diazafluorene-9-one), which is a Ninhydrin analog, and it too reacts to amino acid residues in latent prints.
In reality, AFIS (Automated Fingerprint Identification System) is a computer-based, filing cabinet of known fingerprints. The Maine State Bureau of Identification maintains this "file cabinet". When an unknown fingerprint is developed at a scene or on a piece of evidence, it can be searched through AFIS. AFIS then generates a report of the top 50 fingerprints in the "file cabinet" that are similar to the unknown fingerprint. The latent print examiner then goes through each candidate given by AFIS and if a particular fingerprint looks very similar to the unknown fingerprint, the examiner then requests that fingerprint (on the fingerprint card) from the State Bureau of Identification and does a normal, side-by-side comparison between the actual unknown and the known prints. The only information AFIS gives on candidate fingerprints is the "State Identification Number" which leads to the actual known fingerprint card.
Ninhydrin has been a mainstay for latent print development for several decades. Its original development was to serve as a dye stain for examining body cells under a microscope. It reacts to the presence of amino acids by producing a purple stain.
Iodine fuming is also used for developing prints on porous items, such as paper, cardboard, and raw wood. Iodine fumes react with fat deposits found in fingerprints. When the chemical contacts the fat, it turns the print a brownish color. Iodine evaporates quite rapidly; therefore, developed prints can fade away. Investigators must photograph fingerprints developed with iodine.