Introduction:
A friction or epidermal ridge is a raised portion of the skin on the fingers and toes. Impressions of fingerprints may be left behind on a surface by natural secretions of sweat from glands that are presnet in friction ridge skin.
WOOD GLUE method
AIM: To capture ridge and pore details of your finger using a polymer cast.
Try to take a picture of the print through the eyepiece.
Questions:
- Where are the pores found? Are they regularly spaced?
Pores are found all over our skin and are regularly-spaced across the epidermis layer.
- Are the lines of your print equally spaced thoughout?
Yes, they are equally-spaced throughout
Cyanoacrylate (Superglue) fuming method
Introduction:
The actual development of this chemical method of developing latent fingerprints is somewhat unclear as many agencies and countries claim credit for its discovery. What is generally accepted is that the method came about between 1977 and 1978. It has since been used as an effective technique in many crime laboratories throughout the world.
The basic concept behind all chemical techniques is to apply something that will chemically react with one or more of the constituent chemicals of latent fingerprints. The product of the chemical reaction will render the fingerprints visible and allow the print to be photographed so that identifications can be made.
Superglues typically contain methylcyanoacrylate or ethylcyanoacrylate. They react with traces of amino acids, fatty acids and proteins in the latent fingerprint and the moisture in the air to produce a visible, sticky white substance along the ridges of the fingerprint. The resulting image is then photographed so that comparisons can be made with other fingerprints that are collected.
To enable such a reaction to take place, the cyanoacrylate must be in its gaseous form. Hence, investigators tend to use a fume box to hold the chemicals and objects in an enclosed space. Heat is then applied to allow the superglue to vapourise. If there are any latent fingerprints on the object, the exposure and humidity in the atmosphere will be sufficient to enable the reaction to take place. The actual amount of time required for such a reaction to take place depends on several factors: concentration of cyanoacrylate fumes, humidity levels and size of fume box etc. It is often required to monitor the reaction as it is almost impossible to predict the actual amount of time required for the prints to develop.
AIM: To develop latent prints on a non-porus surface using superglue fuming method.
Questions:
If the contrast of the white print against the black background is still too faint for a good detailed photograph to be captured, what could be done to enhance the fingerprint?
I increase the amount of oil on my finger by pressing it to areas of my face such as my forehead. The sweat from sebaeceous glands on the body and oils contained in perspiration enable the fingerprints to be more distinct .
Iodine fuming method
Introduction:
The iodine fuming method has historically been recognized as one of the earliest techniques used by investigators for developing latent prints. Prior to the introduction of chemical methods such as using ninhydrin and silver nitrate, iodine fuming was a preferred and recommended method to be used on paper products.
While frequently categorised as ‘chemical technique’, the development of latent prints with iodine fumes is not a chemical process but a physical one. Chemical reactions produce new substances and will result in changes of the properties of the constituents of the latent print. Eg. Silver nitrate reacts with the chloride from sodium chloride to form a white precipitate – this creates white lines that make up the latent print.
However, in iodine fuming, natural body fats and oils in the larent print temporarily absorb the iodine vapours. This results in a change in colour, often from colourless to dark brown. This temporary change fades with time as the iodine that is absorb will eventually dissipate into the atmosphere. The colour change can be made permanent by the application of certain materials but the developed latent print can usually be photographed at the greatest inensity of colour change and then allowed to fade.
One advantage of using iodine fuming is that it is an essentially non-destructive technique. No permanent or chemical change has taken place after the print develops. The latent can therefore be further processed using other methods. Additional tests for the constituents of the latent can also be conducted after the print is developed.
AIM: To develop latent prints on a porus surface using iodine fuming method.
Questions:
What are the possible substances that may be used to render the prints more permanent?
Why does the print disappear?
Natural body fats and oils from sebaceous glands temporarily absorb the iodine vapors, resulting in a change in color, from clear to a dark brown, until the effect fades with time. The color change can be made permanent by the application of certain materials.
Powder dusting method
Introduction:
The most commonly known method for developing latent prints would probably be the powder dusting method. A variety of powders are used in dusting for prints. Many of these powders contain aluminium or carbon. The finely crushed powder is gently applied to a surface and the minutes particles of powder cling to the latent residue, making it visible. These prints are then lifted using adhesive tape. For dusting to work, the surface that is being dusted must be completely dry and relatively free of other contamination.
The principle behind dusting is simple. Oils and perspiration form the common residue on fingers that get transferred when a print is made. When the powder is applied to the surface with the print, it sticks to the oils and brings out the ridge patterns.
Dusting is ideal on wood, metal, glass, plastics and tiles. It is less than ideal on paper, cardboard and leather. Powders vary in colour, stickiness, photographic and magnetic qualities. The best colour to to use is one in shart contrast to the surface colour. For example, a white or grey powder works best on a dark surface and a black powder works best on a white or colourless surface. In multicolour situations (such as a magazine cover) it is best to use a fluorescent powder. When the dusted object is exposed to ultraviolet light, the powder will glow, making the print show up regardless of the background colour.
Aim: To develop latent prints using powder dusting method
Questions:
What is magnetic powder dusting and how does it work?
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