powders, fuming-Katherine

Question 1

name 3 types of fingerprint evidence at scene of crime

Answer 1

visible
impression
latent

Question 2

black powder

Answer 2

manufactured from carbon-based powders

adheres to oily residues

applied to many surface types: porous and non-porous

recent advances coat fingerprint powder onto quartz powder or plastic particles

Question 3

white powder

Answer 3

works well on glass, chromed metals, plastic bags and dark coloured surfaces

titanium dioxide powder and an earth powder for base

adheres well to oils of print

excellent contrast to most surfaces

used to use lead carbonate- toxic

Question 4

sliver/grey aluminium powder

Answer 4

performs best on glass, plastic and rubber

aluminium component of the powder adheres to prints on non-traditional surfaces

provides good contrast to the background surface

Question 5

bi-chromatic powders

Answer 5

combination of black and aluminium powders

created to adpat to coloured surfaces

latent prints seen as:

• black ridges on the light parts of the surface
• light ridges on the dark part of the surface

once lifted onto white backing card, they will always appear as dark ridges

Question 6

conventional powders

Answer 6

organic powders

thermoplastic powders

applied with fiber or hair brush

inexpensive, cover 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

Question 7

magnetic based powders

Answer 7

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 rubbed over print surface

image developed with no abrasive contact

Question 8

fluorescent powders

Answer 8

used where a print is difficult to distinguish from its surface

developed for use with any number of alternative light sources ranging from small 1-watt ultraviolet lights to multi-watt lasers

work especially well on raw surfaces

colorants found in fluorescent powders are treated dyes which react to UV and purple/blue bands in visible light spectrum

hues of the powders can be matched to the colour of the surface processed and the wavelength of the light source being used

eliminates any background interference

Question 9

spray powders

Answer 9

tool for specific spot processing

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

Question 10

small particle reagents

Answer 10

suspensions of a powder in water with a detergent

the powder particles adhere to a fingerprint as does a fingerprint powder

Question 11

SPR black

Answer 11

suspension of molybdenedisulfide 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

powder suspension can be sprayed, but small particles can also be submerged in it

can be used on wet/dirty/greasy surfaces

Question 12

SPR UV

Answer 12

suspension of light coloured UV fluorescent pigment in water with a detergent

a light source emitting long wave UV light is needed to view the developed marks in fluorescence

SPR UV provides better contrast on multicoloured surfaces

Question 13

synthetic fiber brushes

Answer 13

introduced in 1950s

examples include glass fiber and tapered polyester

Question 14

powder fineness

Answer 14

powder must be fine enough to show detail of fingerprint

finer powders show greater detail than coarser powders

Question 15

powder adhesion

Answer 15

powder must adhere to the residue of the fingerprint and not adhere to the rest of the surface where it would obscure the view of the print

Question 16

powder sensitivity

Answer 16

how well the powder adheres to a surface

Question 17

powder flow

Answer 17

important that the powder can flow, and does not cake into a solid block which would render it useless

Question 18

iodine fuming

Answer 18

brown/black I2 crystals sublime to give a purple vapour

brown print not stable and needs fixing (starch spray, tetrabase, silver plate, benzoflavone)

I2 also used as a dust or in solution

good for old fingerprints

Question 19

the disadvantage of iodine fuming

Answer 19

I2 was thought to add to double bond of unsaturated fatty acids

Question 20

2011 new use for iodine

Answer 20

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

Question 21

radioactive sulphur dioxide

Answer 21

SO2 gas containing a radioisotopic atom can be used to fume latent fingerprints

visualisation is by autoradiography (image on an x ray film or as a digital image, due to the recent development of scintillation gas detectors)

good for paper, fabrics and adhesive tapes

Question 22

cyanoacrylate fuming

Answer 22

monomer reacts with both eccrine and sebaceous residues

polymerisation on fingerprint ridges

widely used on non-porous surfaces

development of print requires 100 degrees

monomer is irritant

on heating above 220 degrees, toxic HCN gas is given off

portable fuming wands available for field work

enhanced by luminescent or magnetic powders