Powders Flashcards
Visualisation of latent fingerprints
amino acid
- cyanoacrylate ester
- ninhydrin
Visualisation of latent fingerprints
sebaceous/lipidic
- iodine fuming
- small particle reagent
Visualisation of latent fingerprints
eccrine
- cyanoacrylate ester
- silver nitrate
- ninhydrin
Visualisation of latent fingerprints
blood
- leucocrystal violet
- D.A.B
Visualisation of latent fingerprints
fluorescent
- ardrox
- basic yellow 40
- D.F.O
Visualisation of latent fingerprints
non destructive
- iodine fuming
- UV lamp
- Fluorescent lighting
Visualisation of latent fingerprints
porous surfaces
- D.F.O
- iodine fuming
- ninhydrin
Visualisation of latent fingerprints
non-porous surfaces
- cyanoacrylate ester
- small particle reagent
Visualisation of latent fingerprints
glass surfaces and plastic surfaces and metal surfaces and gloss paper and cartridge cases
- cyanacrylate ester
- basic yellow 40
Visualisation of latent fingerprints
wet surfaces
- oil red O
- small particle reagent
Visualisation of latent fingerprints
post-cyanoacrylate
- basic yellow 40
- ardrox
Visualisation of latent fingerprints
post cyanoacrylate cont.
- sudan black
- chelate
Visualisation of latent fingerprints
adhesive tape
- wet powder black
- wet powder white
Visualisation of latent fingerprints
raw wood surfaces
- D.F.O
- iodine fuming
Visualisation of latent fingerprints
post ninhydrin
- small particle reagent
- silver nitrate
Visualisation of latent fingerprints
UV induced
- basic yellow 40
- silver nitrate
3 types of fingerprint evidence at scene of crime
- visible (patent)
- impression (plastic)
- latent
in the past only 4 techniques were used
- powder dusting
- ninhydrin spraying
- iodine fuming
- silver nitrate spraying
difficult circumstances for print visualisation
- wet surfaces
- bloody surfaces
- Multicoloured backgrounds
- Objects with unusual shapes
- Fabrics
- Human skin
- Waxed surfaces
- Untreated wood
- Varnished surfaces
- Cardboard boxes
successful methods target component of residue e.g. water soluble or lipids with success dependent on the following:
latent fingerprint
the surface
environment changes
new methods are based on
new chemical reagents
optical illumination methods
combination of both
order of application
history of finger print powders
- 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
colour selection
- 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.
black powder
- 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
white powder
- works well on glass, chromed metals, plastic bags and dark coloured surfaces.
- adheres well to the oils of the print
silver/grey (aluminium) powder
- 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
bi- chromatic powders
-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.
conventional powders
- 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
magnetic based powders
- 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
magnetic based powders continued
- 1961 – MacDonnell introduces magnetic powders and the Magna Brush
1991 – Wilshire introduces magnetic flakes
fluorescent powders
- 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
fluorescent powders cont.
- 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
spray powders
- a specialized tool for specific spot processing.
- measured portion of powder, blasted from the can, provides enough powder to develop prints without over-processing.
small particle reagents
- 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.
SPR UV
- 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.
synthetic fibre brushes
- introduced in 1950s
e. g glass fibre and tapered polyester
factors influencing fingerprint powder quality
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
chemical fuming- iodine fuming
- 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
2011 new uses for iodine
heating iodine crystals creates fumes that can restore thermal papers that had faded or chemically removed
other fluorescent/fuming techniques
anthranilic acid (fresh prints) anthracenes (old prints)
radioactive sulfur dioxide
SO2 gas containing radioisotopic atom can be used to fume latent finger prints
visualisation is by autoradiography
good for paper fabrics and adhesive tapes
cyanoacrylate fuming
- 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
superglue fuming
- 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
