Chemical Developing of Latent Prints Download

Transcript
Chemical Developing of
Latent Prints
Chemical Developing

Iodine Fuming

Silver Nitrate

Ninhydrin

Cyanoacrylate (super glue)
Forensic Science: Fundamentals & Investigations, Chapter 6
2
Iodine Fuming

Iodine: fumes react with natural body fats and
oils in sebaceous material of a latent print
temporarily absorb the iodine vapors.

This results in a change in color, from clear to
yellow and dark brown, until the effect fades
with time.

Use on porous and non-porous surfaces such as paper,
index cards, magazines, and cardboard
Silver Nitrate

Silver nitrate: reacts with sodium chloride (such as those
salts found in sweat) to form silver chloride.

NaCl + AgNO3  AgCl + NaNO3

Exposing the silver chloride (AgCl) produced by this
reaction to sunlight or an ultraviolet lamp causes the
silver chloride to be reduced to metallic silver, making the
latent prints visible as black or dark gray traces

Used on porous surfaces
Ninhydrin

Ninhydrin: reacts with amino acids to produce a
purple color.
 Ninhydrin
reacts with free amines, such as lysine
(amino acid) residues in fingerprint secretions and
proteins sloughed off, a deep blue or purple color
known as Ruhemann's purple is produced.

Ninhydrin development occurs slowly at room
temperature and humidity. Complete
development may take 24 to 48 hours.
 The
development process can be accelerated by
increasing the temperature and humidity.
 Use on porous surfaces such as paper, tissue, and
clothing
Cyanoacrylate/super glue

Cyanoacrylate: “superglue” in it’s gaseous state, forms a hard,
whitish deposit.

Most liquid super glues are really either methylcyanoacrylate or
ethylcyanoacrylate.

Super glue reacts with the traces of amino acids, fatty acids,
and proteins in the latent fingerprint and the moisture in the
air to produce a visible, sticky white material.

Different colored dusts may be brushed onto the image of the
fingerprint, and they will cling to the sticky white chemical
from which it is formed changing its color.

Used on all non-porous surfaces like metal, glass, and plastic; it
will sometimes work on porous surfaces too, but not as well.