Fingerprint powder
Encyclopedia
Fingerprint powders are fine powders used in dusting for fingerprint
s by crime scene investigators and others in law enforcement. The process of dusting for fingerprints involves various methods intended to get the particles of the powder to adhere to residue left by friction ridge skin on the fingers, palms, or feet.
Physical development of fingerprints using powders is just one of a selection of methods used to develop fingerprints. Fingerprints often leave residues of oils in the shape of the friction ridges, but the friction ridge skin itself does not secrete oils, and so some fingerprints will only leave a residue of amino acids and other compounds which the powder does not adhere to well. For this reason, 'dusting' is used as part of an array of techniques to develop fingerprints, but is often used on larger areas in a crime scene which cannot be removed for analysis, or cannot be subject to more rigorous analysis for other reasons.
Fingerprint powders have various formulations, and the appropriate powder must be used on the appropriate surface. For example, dark coloured powders will show up a fingerprint far better on a light surface.
Magnetic powders are also used, where a fine magnetic powder is held by a magnetic applicator, which may then be gently moved across the fingerprint. As no bristles touch the surface, this often damages the print less than other methods of developing the print.
Some surfaces, such as organic ones, do not take to fingerprint powders at all and use of alternate methods is necessary. Other media, such as certain types of glue, can be "smoked" over these surfaces with fair results.
Historically, Lycopodium powder
, the spore
s of Lycopodium
and related plants, was used as a fingerprint powder.
Fineness: The powder must be fine enough to show the detail of the fingerprint. Finer powders would be theoretically capable of displaying greater detail than coarser powders.
Adhesion: The powder must display the right level of adhesion, so that it will adhere to the residue of the fingerprint (often oils) and not adhere to the rest of the surface where it would obscure the view of the print. When a powder coats a surface, this is known as 'painting'.
Sensitivity: Sensitivity is related to adhesion, and is how well the powder adheres to a surface. For example, aluminum flake is more sensitive than aluminum powder, but greater sensitivity is not always desirable.
Color: The fingerprint powder must be a suitable color for the surface in question.
Flow: To a lesser extent, it is important that the powder can flow, and does not 'cake' into a solid block, which would render it useless.
As these various qualities are not normally all present in any one material, compositions of various materials are generally used. For example, lampblack is particularly black in color, absorbing around 98% of incident visible light, but other materials may have greater adhesion, or flow more effectively, producing a better overall powder than either alone.
Of these, one of the more common powders in current use is aluminium powder, as it will show up on a variety of surfaces.
Fingerprint
A fingerprint in its narrow sense is an impression left by the friction ridges of a human finger. In a wider use of the term, fingerprints are the traces of an impression from the friction ridges of any part of a human hand. A print from the foot can also leave an impression of friction ridges...
s by crime scene investigators and others in law enforcement. The process of dusting for fingerprints involves various methods intended to get the particles of the powder to adhere to residue left by friction ridge skin on the fingers, palms, or feet.
Physical development of fingerprints using powders is just one of a selection of methods used to develop fingerprints. Fingerprints often leave residues of oils in the shape of the friction ridges, but the friction ridge skin itself does not secrete oils, and so some fingerprints will only leave a residue of amino acids and other compounds which the powder does not adhere to well. For this reason, 'dusting' is used as part of an array of techniques to develop fingerprints, but is often used on larger areas in a crime scene which cannot be removed for analysis, or cannot be subject to more rigorous analysis for other reasons.
Fingerprint powders have various formulations, and the appropriate powder must be used on the appropriate surface. For example, dark coloured powders will show up a fingerprint far better on a light surface.
Application
Powders may be applied with a fingerprint brush, a brush with extremely fine fibers designed to hold powder, and deposit it gently on the fingerprint to be revealed, without rubbing away the often delicate residue of the fingerprint itself. They may also be applied by blowing the powder across the fingerprint, or by pouring the powder onto the print, and then blowing away the excess.Magnetic powders are also used, where a fine magnetic powder is held by a magnetic applicator, which may then be gently moved across the fingerprint. As no bristles touch the surface, this often damages the print less than other methods of developing the print.
Composition
Modern fingerprint powders have a variety of compositions, and are often a matter of personal choice by the expert using them or down to the standard procedure of the department or agency. Many agencies use proprietary powders produced by independent companies, and so the exact formulation of these powders is not revealed.Some surfaces, such as organic ones, do not take to fingerprint powders at all and use of alternate methods is necessary. Other media, such as certain types of glue, can be "smoked" over these surfaces with fair results.
Historically, Lycopodium powder
Lycopodium powder
Lycopodium powder is a yellow-tan dust-like powder historically used as a flash powder. It is composed of the dry spores of clubmoss plants, various fern relatives principally in the genera Lycopodium and Diphasiastrum...
, the spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s of Lycopodium
Lycopodium
Lycopodium is a genus of clubmosses, also known as ground pines or creeping cedar, in the family Lycopodiaceae, a family of fern-allies...
and related plants, was used as a fingerprint powder.
Factor influencing fingerprint powder quality
There are several factors influencing the effectiveness of fingerprint powders.Fineness: The powder must be fine enough to show the detail of the fingerprint. Finer powders would be theoretically capable of displaying greater detail than coarser powders.
Adhesion: The powder must display the right level of adhesion, so that it will adhere to the residue of the fingerprint (often oils) and not adhere to the rest of the surface where it would obscure the view of the print. When a powder coats a surface, this is known as 'painting'.
Sensitivity: Sensitivity is related to adhesion, and is how well the powder adheres to a surface. For example, aluminum flake is more sensitive than aluminum powder, but greater sensitivity is not always desirable.
Color: The fingerprint powder must be a suitable color for the surface in question.
Flow: To a lesser extent, it is important that the powder can flow, and does not 'cake' into a solid block, which would render it useless.
As these various qualities are not normally all present in any one material, compositions of various materials are generally used. For example, lampblack is particularly black in color, absorbing around 98% of incident visible light, but other materials may have greater adhesion, or flow more effectively, producing a better overall powder than either alone.
Examples of fingerprint powders
Some materials and compositions that have traditionally been used as fingerprint powders:White
- Calcium oxideCalcium oxideCalcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
- ChalkChalkChalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
- Haddonite White (titanium dioxideTitanium dioxideTitanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...
, 4 parts; kaolin, 1 part; French chalkFrench chalkFrench chalk is a form of steatite.As an arist's material the term is used by Max Doerner in his book "The Materials of the Artist" where he describes a calcium carbonate used to make traditional gesso primer, to be painted over...
, 1 part; or titanium dioxide, 60%; purified talc, 20%; and kadin lenis, light 20%). - Lanconide (zinc sulfideZinc sulfideZinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...
, 4 parts; zinc oxide, 4 parts; barium sulfateBarium sulfateBarium sulfate is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it...
, 4 parts; titanium dioxideTitanium dioxideTitanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...
, 4 parts; bismuth oxychlorideBismuth oxychlorideBismuth oxychloride is a chemical compound of bismuth, oxygen, and chlorine, with the formula BiOCl. It exists in nature as the mineral bismoclite which is part of the matlockite mineral group.-Structure:...
, 4 parts; and calcium carbonateCalcium carbonateCalcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, 1 part) - Mercury-chalk (hydrargyrum-cum-creta) now no longer used, as it represents a serious health risk.
- Titanium dioxideTitanium dioxideTitanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...
- White tempera (starchStarchStarch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
, and titanium dioxideTitanium dioxideTitanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...
)
Black
- CharcoalCharcoalCharcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
- Dactyl black (graphiteGraphiteThe mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
, lampblackCarbon blackCarbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
, and gum acacia) - Dragon's bloodDragon's bloodDragon's blood is a bright red resin that is obtained from different species of a number of distinct plant genera: Croton, Dracaena, Daemonorops, Calamus rotang and Pterocarpus. The red resin was used in ancient times as varnish, medicine, incense, and dye...
(powdered resin of the Daemonorops draco plant) - GraphiteGraphiteThe mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
- Haddonite black (lampblackCarbon blackCarbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
70%; graphite 20%; and powdered acaciaAcaciaAcacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...
10%) - LampblackCarbon blackCarbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
- Photocopier toners
Others
- AluminiumAluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
powder - Fluorescent powders
- LycopodiumLycopodiumLycopodium is a genus of clubmosses, also known as ground pines or creeping cedar, in the family Lycopodiaceae, a family of fern-allies...
- Magnetic powders
- Metal powders
Of these, one of the more common powders in current use is aluminium powder, as it will show up on a variety of surfaces.