Latent Print Development Using Iodine Fuming
It is widely believed that Iodine fuming was the first, or at least among the first chemical methods for developing latent fingerprints. Iodine is a non-metal, crystalline element that was first isolated in 1811 by the French chemist Barnard Courtois.
The name originates from the Greek word for violet, iodes, and while this element is lustrous metallic gray in color, it gives off a violet/purple gas when heat is applied. In its pure state, iodine is highly toxic by ingestion or inhalation of the fumes. Compounds containing iodine are used in water purification tablets and the radioactive isotope of iodine is used in thyroid gland treatment. Iodized salt is a regular on most dinner tables.
Iodine occupies a prominent place on the shelves of many crime laboratories. Those purple fumes are known to react with body oils to produce an orange/brown stain. This is especially valuable in the development of latent prints on porous materials such as untreated wood, paper, cardboard and certain types of cloth.
Iodine fuming works best on prints known to be reasonably fresh, since the body oils tend to disperse rather quickly in porous materials so the ridge detail becomes useless. Thus—ransom or demand notes (this is a stick-up) are likely targets for iodine fuming. If this technique works, the developed prints must be quickly photographed as they are “fugitive,” in that they begin to fade shortly after they appear.
Iodine fuming is then, the ideal first step in latent development on porous materials. It does not interfere with subsequent processing with DFO, Ninhydrin or Physical Developer.
No complicated or expensive apparatus is needed to start the fuming process. A fuming chamber may be as simple as a Zip-Top plastic bag. Simply insert the document to be examined into the bag with a few iodine crystals, zip it shut and apply heat by cupping one hand over the crystals for 10-15 seconds. Body heat kicks off the “sublimation” process, which converts the solid material into a purple gas. For safety sake, wear latex gloves, safety goggles and an organic vapor respirator.
Learn more from the Technical Bulletin: Overview of Latent Print Development Techniques
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