Download Types of Prints and Visualizing Prints

Types of Prints and Developing
Prints
Unit II
Types of Prints: Plastic
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Molded or indented print
Made from pressing a finger into a
moldable material such as:
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Paint
Putty
Gum
Stamps
Softened candy bars
Candle wax
Types of Prints: Visible
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Left by a finger that touched a colored
substance such as:
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Blood
Dust
Paint
Mud
Grease
Chalk
Types of Prints: Latent
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Invisible to the eye.
Result from oil and water deposited from
sweat pores on fingertips.
Must be developed by chemical or
physical means
Developing Latent Prints
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There are several methods to
develop latent prints. The method
used depends on the surface you
think the print might be on.
Surfaces and Method Used
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Surface: Hard, non-absorbent surfaces
such as glass, painted wood, tiles…
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Method: Dusting or Superglue
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Note: Choose a dusting powder that will stand out
against the surface in question.
Surfaces and Method Used
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Surface: Soft, porous surfaces such as
Styrofoam, paper, leather…
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Method: Iodine, Ninhydrin, Silver Nitrate
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Note: The silver nitrate method is the same
method used to develop pictures.
Dusting
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Regular dust with a fiberglass brush
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Magnetic dust with a magnetic brush
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Fluorescent dust with a fiberglass brush
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Magnetic Fluorescent dust with a magnetic brush
What is fluorescence?
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It occurs when a material absorbs light
and then re-emits it at a longer
wavelength than the light source.
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Usually use a UV (ultraviolet) light
source.
Can be high for low frequency UV
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Fluorescent Powder
Iodine (I2) Fuming
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Iodine sublimes (solid to a gas) when heated.
The material in question is placed in a closed
container with I2 and heated. The I2 reacts
with the oils in the print to make it visible.
Once the process is stopped, the print will
begin to fade.
It must be photographed or sprayed with a
1% solution of starch in water, which will turn
the print blue and make it last for several
weeks to several months.
Iodine (I2) Fuming
Silver Nitrate (AgNO3)
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Silver nitrate reacts with the salt in your sweat.
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Reaction: AgNO3 + NaCl  AgCl + NaNO3
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Reasoning: The silver chloride (AgCl) produced is
colorless, but when it is exposed to UV light, the
print looks reddish-brown or black.
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Caution: be careful of skin exposure.
Silver Nitrate (AgNO3)
Ninhydrin
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This is a chemical reaction between the ninhydrin
compound and the trace amounts of amino acids
(building blocks of proteins) from your sweat.
The reaction produces a purple-blue print.
The reaction takes several hours, but is catalyzed
(goes faster) with heat.
Ninhydrin is sprayed on material.
Caution: be careful of skin exposure.
Ninhydrin
Superglue Fuming
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Super Glue is approximately 98 to 99 percent
cyanoacrylate.
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Cyanoacrylate fumes can be created when a
Super Glue fuming chamber is made by putting the
glue, the material, and a heat source in a tank.
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The fumes and the suspect material are contained
within an enclosed chamber for up to 6 hours.
Superglue Fuming