How Police Find Latent Fingerprints – Part 2 – Latent Print Powders

Part 1 of this series we presented an outline of what a latent print is, and an outline of latent print processing strategies. This article will provide an explanation for the numerous varieties of powders used to increase latent prints and their precise makes use of. One of the primary acknowledged strategies for developing latent prints used black powder made from lamp black or soot (carbon black) and white talc. The powder clings to the moisture content material of the latent print as defined in Part 1. Dark powders are used on light-coloured surfaces and mild coloured powders are used on dark surfaces as a way to deliver visual and photographic assessment. Listed below are the very fundamental powders that have been in use during the sector for decades. Latent print powders are divided into the subsequent 5 classes: Author’s Note: All of the powders listed beneath are applied with a soft bristle brushes inclusive of squirrel hair, goat hair, fiberglass, make-up style brushes, and many others. More on this will be supplied in a moment.

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Oxide powders: This formulation is usable on many non-porous (STICK) surfaces inclusive of maximum metals, painted wood, plastics and glass. Some examples are: Black, White, Red and Gray. These powders aren’t endorsed for use on particularly polished (SLIP) surfaces which include chrome, silver, and many others. Oxide powders are known as “SLIP” powders, and are endorsed to be used on “STICK,” non-porous surfaces.
Special oxide formulations are important for precise “trouble” surfaces like zinc-plated (galvanized) metal used to make vending machine coin boxes.

Metallic powders, as the call implies, are formulated the usage of diverse metals like aluminum, brass and copper. Metallic powders are endorsed for use on particularly polished (SLIP) surfaces. Latent prints on chrome-plated metal or silver are commonly destroyed (wiped away) if oxide powders are used. Metallic powders are called STICK powders as they keep on with latents on SLIP (slippery) surfaces, and they have to now not be used on STICK surfaces because the powder tends to stick to the entire surface and now not simply the ridge systems present.
Combination powders: Combinations are created via a specific formulation of oxide and metal powders. An instance is the very famous Silver/Black latent powder. This is a mixture of aluminum (steel) and black (oxide) powders. The gain is that aggregate powders can be used on definitely any non-porous surface. Another specific characteristic supplied via this form of powder is that on darkish surfaces the evolved latent prints seem in a light coloration and on mild surfaces the prints might be dark. If your budget is seriously restricted, and also you require a flexible, extraordinarily useful and powerful powder, use a combination-formulated powder inclusive of Silver/Black, Silver/ Gray or Silver/Red. This will put off having to carry several extraordinary oxide and steel powder formulations.
Fluorescent powders: This category of powders hire a base substance this is fluorescent in nature whilst uncovered to extremely violet (black) mild or alternate light resources like blue mild. Fluorescent powders are taken into consideration to be oxide in their residences and are excellent used on non-polished surfaces. The particular benefit of a fluorescent powder is the fact that it may be used on multi-colored, patterened backgrounds. When the vicinity under scrutiny is darkened, and an exchange light supply is used, the fluorescent cloth emits a exquisite glow that well-knownshows the fingerprint ridges, and the background all however disappears-making photography easier to accomplish.
Magnetic powders: Magnetic powders first seemed in the marketplace at some stage in the early 1970s. Magnetic formulations include iron or iron oxide because the fundamental component. Various pigments are delivered to provide background assessment. White, black, silver and red are commonly available. Some manufacturers additionally provide aggregate formulation as well as fluorescent magnetic powders. The principle advantage of a magnetic powder is that it’s miles implemented by using a magnetic applicator wand and no longer a broom. The wand is ready with a sturdy magnet and while held approximately a -inch or so above the powder, the powder is interested in the magnet and bureaucracy a powder brush. Thus-handiest the powder touches the floor being dusted, and this may put off any chance of destructive the delicate latent print at the surface. Magnetic powders aren’t recommended to be used on surfaces containing iron or metal.
There are a several sorts of feather dusters to be had to be used in area of a brush. Many CSIs, prefer feather dusters while making use of fluorescent powders. They are also a treasured device in “cleaning up” or doing away with excess powder from latents advanced the use of a broom. Application Procedures: As referred to above, most effective magnetic powder is applied with out a brush. The remaining powders require use of a tender bristle brush. Brushes using fiberglass or carbon-fiber strands are idea to be the softest. Applying powder or dusting the surface is achieved using these endorsed steps:
1. After figuring out which formula to use, measure out a small quantity of powder onto a clean sheet of paper. Do no longer dip the comb without delay into the powder jar as this tends to compact the powder, and it will also upload contamination from previously dusted surfaces into the powder.
2. The first-class rule to observe in terms of using powder is “Less Is Best.” Pickup the powder with the tip of the bristles, and lightly tap off any excess powder.
Three. Apply the powder to the surface in mild sweeping strokes. Some CSIs use a from side to side, side to side motion-a few users twirl the comb between the thumb and index finger. Practice applying powder to numerous surfaces before attempting to use those methods at an actual crime scene. Learn what works great for you.
Four. As developed latents appear, make bigger the quest place by way of making use of extra powder. Remember, you’re processing areas that possibly had been touched.
5. After prints are advanced they should be photographed earlier than any attempt is made to “raise” them. Be certain to encompass a scale (ruler) in each picture. This is a necessity specially if digital cameras are used on the scene. If the latents recovered are to be submitted to an internet seek together with the Automated Fingerprint Identification System (AFIS), the entries have to be 1:1 in size. A scaled photo makes this viable. After pictures are taken, the advanced latents can be lifted from the surface. Numerous techniques are to be had for this motive.

Included in this arsenal of lifting techniques are: latent print lifting tapes (available in 1-inch to 4-inch widths, Hinge Lifters, EZ-Lifters and Rubber/Gel Lifters. And take into account that you will need backing playing cards while making lifts with lifting tapes.An precise description of the lifting manner is mentioned at the internet site listed under. So there you’ve got it. But I’ll close this newsletter with some warnings:

Be certain to gain a Material Safety Data Sheet (MSDS) from the powder producer. Some powders contain dangerous substances which you must be made aware about. The MSDS will provide an explanation for what safety precautions you need to take to protect yourself which includes wearing a dirt respirator, eye protection, latex gloves and a disposable jumpsuit or lab apron.
Another precaution is to bear in mind the mess you can leave at the back of. Most latent powder producers get frequent smartphone calls from irate home and commercial enterprise owners who locate it subsequent to impossible to easy up the powder left in the back of. Black latent powders are especially hard, if no longer impossible, to cast off from carpets, furnishings and other substances.