There are three basic types of fingerprints—latent, patent, and impressed. The prints we see with the naked eye are called patent prints. These visible fingerprints are left in some sort of medium, such as dust, ink, and even blood.
Impressed prints are actual fingerprint indentations left in substances such as, putty, paint, and wax.
Finally, latent prints are the invisible prints formed by sweat, amino acids, and oils in the skin.
Latent prints are the ones most associated with crime scenes, because they’re the ones we see TV CSI folks going after like they’re applying a coat of Sears Weatherbeater paint. There’s a technique to dusting and lifting a latent fingerprint, and vigorously mopping on the powder as seen on TV is not it. Gently is the keyword when it comes to dusting for prints. Gentle brush strokes (preferably from a camel hair brush) and swirls. Those of you attending the Writers’ Police Academy will get chance to learn and perform the proper techniques.
Common fingerprint powders are fairly easy to use since they stick to water, oils, and fat deposits. Most of you are aware that the most common fingerprint powders are black (for use on lighter surfaces) and white (for use on darker surfaces). But how about a surface that’s wallpapered in some sort of wacky pattern? Well, then it’s time to bring out florescent powders. The process the same—dusting—but the developed prints must be viewed with an alternate light source.
Portable MicroBlue Alternate Light Source (fits in shirt pocket)
Magnetic powders can be used when investigators are worried about the possibility of damaging a print by using the normal brushing techniques. These powders contain very small bits of metal. A magnetic wand/applicator is used to pick up the powder, and is then released onto the print by touching the tip on the opposite end of the wand.
Sudan black – Great for locating and lifting prints from greasy items, such as fast food wrappers, and in fast food restaurants.
Dawn dish detergent
works great when developing prints on tape (Christmas wrapping tape, etc.). Mix 20 drops of the detergent, 20 drops of water, and .5 grams of black fingerprint powder. Mix the ingredients together until they become foamy, like shaving cream (sort of), and then use a camel hair brush to apply to the surface you want to print (you can paint the surface this time). Wait until the foam has completely dried and then rinse. Presto! There’s your print. By the way, this works well on latex gloves, too.
Detective’s cabinet containing various powders, lifting tapes, and brushes