why do fingerprints cause smudges on surfaces such as glass?
In: Biology
Because the skin secretes small amounts of oil. There is more in some places than others, the forehead and the side of the nose for instance. Spend too much time with your hands in detergent and the oil gets washed away leaving you with dry feeling skin.
The oil from the skin is deposited in the shape of the fingerprint ridges. Criminal investigators will lightly dust an area with a fine powder and there’ll stick to the grease and turn the hardly visible “latent” print into one that can be photographed
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