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Imaging and Photography > Powders > Flashcards

Powders Flashcards

1
Q

Visualisation of latent fingerprints

amino acid

A
  • cyanoacrylate ester

- ninhydrin

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2
Q

Visualisation of latent fingerprints

sebaceous/lipidic

A
  • iodine fuming

- small particle reagent

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3
Q

Visualisation of latent fingerprints

eccrine

A
  • cyanoacrylate ester
  • silver nitrate
  • ninhydrin
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4
Q

Visualisation of latent fingerprints

blood

A
  • leucocrystal violet

- D.A.B

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5
Q

Visualisation of latent fingerprints

fluorescent

A
  • ardrox
  • basic yellow 40
  • D.F.O
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6
Q

Visualisation of latent fingerprints

non destructive

A
  • iodine fuming
  • UV lamp
  • Fluorescent lighting
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7
Q

Visualisation of latent fingerprints

porous surfaces

A
  • D.F.O
  • iodine fuming
  • ninhydrin
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8
Q

Visualisation of latent fingerprints

non-porous surfaces

A
  • cyanoacrylate ester

- small particle reagent

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9
Q

Visualisation of latent fingerprints

glass surfaces and plastic surfaces and metal surfaces and gloss paper and cartridge cases

A
  • cyanacrylate ester

- basic yellow 40

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10
Q

Visualisation of latent fingerprints

wet surfaces

A
  • oil red O

- small particle reagent

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11
Q

Visualisation of latent fingerprints

post-cyanoacrylate

A
  • basic yellow 40

- ardrox

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12
Q

Visualisation of latent fingerprints

post cyanoacrylate cont.

A
  • sudan black

- chelate

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13
Q

Visualisation of latent fingerprints

adhesive tape

A
  • wet powder black

- wet powder white

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14
Q

Visualisation of latent fingerprints

raw wood surfaces

A
  • D.F.O

- iodine fuming

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15
Q

Visualisation of latent fingerprints

post ninhydrin

A
  • small particle reagent

- silver nitrate

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16
Q

Visualisation of latent fingerprints

UV induced

A
  • basic yellow 40

- silver nitrate

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17
Q

3 types of fingerprint evidence at scene of crime

A
  • visible (patent)
  • impression (plastic)
  • latent
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18
Q

in the past only 4 techniques were used

A
  • powder dusting
  • ninhydrin spraying
  • iodine fuming
  • silver nitrate spraying
19
Q

difficult circumstances for print visualisation

A
  • wet surfaces
  • bloody surfaces
  • Multicoloured backgrounds
  • Objects with unusual shapes
  • Fabrics
  • Human skin
  • Waxed surfaces
  • Untreated wood
  • Varnished surfaces
  • Cardboard boxes
20
Q

successful methods target component of residue e.g. water soluble or lipids with success dependent on the following:

A

latent fingerprint
the surface
environment changes

21
Q

new methods are based on

A

new chemical reagents
optical illumination methods
combination of both
order of application

22
Q

history of finger print powders

A
  • Early versions were handmade
  • early 1900’s - commercially-available powders
  • Colours limited to black and aluminum
  • Examiners used a very bright light to visualize the prints
  • 1977 – Morris and Wells patent a reagent called Small Particle Reagent (SPR)
  • 1992 – a black powder suspension was demonstrated to Darren Burns by Atsushi Shirakami
  • This powder suspension would later be marketed by Lightning Powder Company as Sticky-side Powder™
  • 1993 – ZnCO3-based white PS introduced by Frank et al.
  • 1995 – Springer et al. introduce a fluorescent PS
23
Q

colour selection

A
  • black powder is still a staple
  • Nowadays use a coloured powder to provide a visual contrast
  • Colours such as white, silver/gray (aluminum) or Bi-Chromatic™ are now used for almost any surface that may be encountered.
24
Q

black powder

A
  • manufactured from carbon-based powders
  • adheres to the oily residues
  • can be applied to many surface types: porous and non-porous alike.
  • recent advances coat the fingerprint powder onto quartz powder or plastic particles
25
Q

white powder

A
  • works well on glass, chromed metals, plastic bags and dark coloured surfaces.
  • adheres well to the oils of the print
26
Q

silver/grey (aluminium) powder

A
  • performs best on glass, plastic and rubber
  • aluminium component of the powder adheres to prints on non-traditional surfaces
  • provides good contrast to background surfaces
27
Q

bi- chromatic powders

A

-combination of black and aluminum powders,
-created to adapt to coloured surfaces.
-latent prints seen as:
black ridges on the light parts of the surface and
light ridges on the dark part of the surface.
- Once these prints are lifted onto a white backing card, they will always appear as dark ridges.

28
Q

conventional powders

A
  • applied with a fiber or hair brush, used at SOC
  • inexpensive, cover a large area and develop prints on most non-porous surfaces.
  • drawback is that they are very light and airy and can become easily airborne making a mess
29
Q

magnetic based powders

A
  • colorants wrapped around iron filings.
  • applied with a magnet embedded inside a plastic or non-ferrous metal wand creating a ball of powder
  • iron fillings are “rubbed” over the print surface, the colorant is deposited on the oily residue.
  • image developed with no abrasive contact to the residue
  • Ideal for more delicate type evidence.
  • used on some porous surfaces and non-porous surfaces
30
Q

magnetic based powders continued

A
  • 1961 – MacDonnell introduces magnetic powders and the Magna Brush

1991 – Wilshire introduces magnetic flakes

31
Q

fluorescent powders

A
  • used where a print is difficult to distinguish from its surface.
  • Developed for use with any number of alternate light sources
  • work especially well on raw surfaces
  • The colorants found in fluorescent powders are treated dyes which react to UV and purple/blue bands in the visible light spectrum
32
Q

fluorescent powders cont.

A
  • The hues of the powders can be matched to the colour of the surface processed and the wavelength of the light source being used.
  • This eliminates any background interference
33
Q

spray powders

A
  • a specialized tool for specific spot processing.

- measured portion of powder, blasted from the can, provides enough powder to develop prints without over-processing.

34
Q

small particle reagents

A
  • suspensions of a powder in water with a detergent.
  • the powder particles adhere to a fingerprint as does a fingerprint powder

SPR Black

  • suspension of molybdenedisulfide (MoS2) powder in water with a detergent.
  • Crystal structure of powder has significant effect on development of prints
  • Gives grey, shiny prints that can be lifted (after drying)

can be used on wet and/or dirty/greasy surfaces.

35
Q

SPR UV

A
  • suspension of light coloured UV fluorescent pigment in water with a detergent.
  • a light source emitting long wave UV light (365 nm) is needed to view the developed marks in fluorescence.
  • provides better contrast on multi coloured surfaces.
36
Q

synthetic fibre brushes

A
  • introduced in 1950s

e. g glass fibre and tapered polyester

37
Q

factors influencing fingerprint powder quality

A

fineness
- the powder must be fine enough to show detail

adhesion
- powder must adhere to the residue

when a powder coats a surface this is known as painting

sensitivity
- how well the powder adheres to the surface

colour
- the fingerprint must be a suitable colour for the surface in question

flow
It is important that the powder can flow and doesn’t cake

38
Q

chemical fuming- iodine fuming

A
  • used for over 100 yrs
    black crystal sublime to give purple vapour
    physical scorption to give a brown print
  • brown print is not stable and needs fixing starch spray, tetra base, silver plat. benzoflavone makes it go purple
  • iodine used as a dust or solution good for old finger prints
39
Q

2011 new uses for iodine

A

heating iodine crystals creates fumes that can restore thermal papers that had faded or chemically removed

40
Q

other fluorescent/fuming techniques

A 
anthranilic acid (fresh prints)
anthracenes (old prints)
41
Q

radioactive sulfur dioxide

A

SO2 gas containing radioisotopic atom can be used to fume latent finger prints

visualisation is by autoradiography

good for paper fabrics and adhesive tapes

42
Q

cyanoacrylate fuming

A
  • 1942 – Harry Coover works with CA monomers
  • 1958 – Eastman markets new material as Super Glue
  • 1977 – Fuseo Matsumura notices prints developed on CA mounted slides
  • 1979 – LW Wood notices prints developed on film tank repaired with CA
  • 1980 – Louis Bourdon applies for patent for the CA/LP process
  • 1981 – U.S. patent 4,297,383 issued; injunction awarded to U.S. Army JAG
43
Q

superglue fuming

A
  • Monomer reacts with eccrine and sebaceous residues
  • Polymerisation on fingerprint ridges
  • Widely used on non-porous surfaces
  • Developed by Japanese Police Agency in 1978
  • Development of print requires 100°C and RH
  • Monomer is an irritant
  • On heating above 220°C toxic HCN gas is given off
  • Portable fuming wands available for field work
  • Enhanced by luminescent stains or magnetic powders

Imaging and Photography (20 decks)

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