There are three main types of fingerprints: visible prints, latent prints and impressed prints. Visible prints are also called patent prints and are usually left in some medium that reveals them to the naked eye. They can be formed when substances such as blood, dirt, ink or oils on the finger come into contact with a smooth surface a leave an impression that is visible without development.
Impressed prints are also called plastic prints and are indentations left in soft pliable surfaces, such as clay, wax, paint or other surface that will hold the impression. They are visible and can be viewed or photographed without development.
Latent prints usually refer to prints that are not apparent to the naked eye. They are formed from the sweat from sebaeceous glands on the body or water, salt, amino acids and oils contained in sweat. The various fluids create prints that must be developed before they can be seen or photographed. They can be made sufficiently visible by disting, fuming or chemical reagents.
In our lab lesson, we focused on developing latent prints and visible prints. Here are the methods that can be used to expose latent prints. The bolded ones are the methods that we tried out in the lab.
- Cyanoacrylate (Superglue) fuming method
- Wood Glue method: using a polymer cast to capture ridge & pore details
- Iodine fuming method: using iodine, which is absorbed by natural body fats & oil in the fingerprint to change colour temporarily.
- Powder dusting method: using powders
- Magna Brush: using magnetic properties (iron)
- Ninhydrin: using a chemical that reacts to amino acids
- Silver Nitrate: using the property of silver chloride (sodium chloride in sweat) under light
- Amido Black: using a chemical to develop prints in BLOOD!
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