Latent prints
Although the word latent means hidden or invisible, in modern usage for forensic science the term latent prints means any chance or accidental impression left by ridges in the skin on a surface, regardless of whether it is visible or invisible at the time of deposition. Electronic, chemical and physical processing techniques permit visualization of invisible latent print residues whether they are from natural sweat on the skin or from a contaminant such as motor oil, blood, ink, paint or some other form of dirt. The different types of fingerprint patterns, such as arch, loop and whorl, is described below.
Patent prints
Patent prints are chance friction ridge impressions which are obvious to the human eye and which have been caused by the transfer of foreign material from a finger onto a surface. Some obvious examples would be impressions from flour and wet clay. Because they are already visible and have no need of enhancement they are generally photographed rather than being lifted in the way that latent prints are. An attempt to preserve the actual print is always made for later presentation in court, and there are many techniques used to do this. Patent prints can be left on a surface by materials such as ink, dirt, or blood.
Plastic prints
A plastic print is a friction ridge impression left in a material that retains the shape of the ridge detail. Although very few criminals would be careless enough to leave their prints in a lump of wet clay, this would make a perfect plastic print. Commonly encountered examples are melted candle wax, putty removed from the perimeter of window panes and thick grease deposits on car parts. Such prints are already visible and need no enhancement, but investigators must not overlook the potential that invisible latent prints deposited by accomplices may also be on such surfaces. After photographically recording such prints, attempts should be made to develop other non-plastic impressions deposited from sweat or other contaminants.
1. Arch
In arches, the ridges of the finger run continuous from one side of the finger to the other with no curving. There are two sub-groups that further define the arch pattern:
Plain Arch - this pattern has a consistency of flow to it. It starts on one side of the finger, and then the ridge cascades upward slightly, almost resembling a wave out on the ocean. The plain arch then continues its journey along the finger to the other side. The plain arch is the simplest of the fingerprint patterns to discern.
Tented Arch - this pattern is similar to the plain arch in that it starts on one side of the finger and flows out in a similar pattern to the other side. However, the difference in the tented arch lies in the ridges in the center, which are not continuous as in the case of the plain arch. The ridges, which adjoin each other in the center, converge and thrust upward, giving the impression of a pitched tent.
2. Loop
In loops, the ridges make a backward turn but do not twist. This backward turn, or loop, is differentiated by how the loop flows on the hand and not how it flows on the card on which the imprint is taken. The imprint on the fingerprint card is similar to the reverse image we see when we look in the mirror at ourselves. There are two sub-groups that were identified in this category:
Radial Loop - these are loops that flow toward the radius bone of the hand or, in other words, when the downward slope of the loop is from the direction of the little finger toward the thumb of the hand.
Ulnar Loop - these are loops that flow toward the ulna bone of the hand or, in other words, when the downward slope of the loop is from the direction of the thumb toward the little finger of the hand.
1. Arch
In arches, the ridges of the finger run continuous from one side of the finger to the other with no curving. There are two sub-groups that further define the arch pattern:
Plain Arch - this pattern has a consistency of flow to it. It starts on one side of the finger, and then the ridge cascades upward slightly, almost resembling a wave out on the ocean. The plain arch then continues its journey along the finger to the other side. The plain arch is the simplest of the fingerprint patterns to discern.
Tented Arch - this pattern is similar to the plain arch in that it starts on one side of the finger and flows out in a similar pattern to the other side. However, the difference in the tented arch lies in the ridges in the center, which are not continuous as in the case of the plain arch. The ridges, which adjoin each other in the center, converge and thrust upward, giving the impression of a pitched tent.
In loops, the ridges make a backward turn but do not twist. This backward turn, or loop, is differentiated by how the loop flows on the hand and not how it flows on the card on which the imprint is taken. The imprint on the fingerprint card is similar to the reverse image we see when we look in the mirror at ourselves. There are two sub-groups that were identified in this category:
Radial Loop - these are loops that flow toward the radius bone of the hand or, in other words, when the downward slope of the loop is from the direction of the little finger toward the thumb of the hand.
Ulnar Loop - these are loops that flow toward the ulna bone of the hand or, in other words, when the downward slope of the loop is from the direction of the thumb toward the little finger of the hand.
3. Whorls
In whorls, there are patterns in which there are two or more deltas (first ridge nearest the divergence point of two type lines) and there exists a recurve preceding each delta. There are four sub-groups of whorls:
Plain Whorl - in these whorls, the ridges make a turn of one complete circuit and, therefore, are circular or spiral in shape. The plain whorl is the simplest form of whorl and the most common. There are at least two deltas and a ridge whose circuit may be spiral, oval or circular in shape.
Non- Porous
Prints are easily left on non-porous surfaces such as glass, wood, and painted areas. In order to recover those prints, the method of dusting is normally required.
Dusting is a common method to find fingerprints on non-porous surfaces. It starts by the area where the print is located and then is lightly dusted with a dusting brush. Thereafter, the corresponding colored powder is applied then lifted with tape and set against a contrasting background to make the print easily visible.
Black Dust: White or Light colored Surfaces
Grey or White Dust: Dark Surfaces
Fluorescent Dust: Multi-Colored Surfaces
Magnetic Dust: Leather or Rough Surfaces
Porous
Prints left on fiber-like surfaces such as paper,cloth or blinds are called porous. In order to recover these prints, the use of chemicals are necessary. Various chemical methods for recovering fingerprints are Iodine Fuming, Ninhydrin, Silver Nitrate, and Super Glue Fuming.
Iodine Fuming—The material that needs to be fingerprinted is placed into an enclosed cabinet along with iodine crystals. The crystals are heated and soon turn into a gaseous vapor. The vapor then causes the prints to appear.
Ninhydrin- This method starts by spraying the chemical onto the surface of the material via an aerosol can. After a few hours, the prints begin to become visual. This process can be accelerated if the prints are heated up after application of the chemical.
Silver Nitrate- Mostly used as a last resort method when both Iodine Fuming and Silver Nitrate have failed. The silver nitrate is sprayed onto the surface of the porous material and is then left to dry. It is later exposed to ultraviolet light, which exposes the prints and allows examination.
Super Glue Fuming (also used on non-porous materials)-Super glue is placed on cotton and is treated with sodium hydroxide. The fumes are then created by heating the treated cotton.The fumes and object are placed inside a heated chamber for up to six hours and the fumes adhere to the print, exposing it.
Great information, and great pictures! It is clear you took your time on this post. The information is very clear and well presented. Overall a very good post
ReplyDeleteGood on it, I like the info/pic arrangement. Well researched
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