fig1 shows a diagram of an apparatus 2 for detecting a latent fingerprint 50 ( not shown in fig1 ) on a sample material 10 clamped within the apparatus 2 . the apparatus 2 includes a supporting frame 24 , a pair of circular plates or disks 14 rotatably mounted to opposing portions of the supporting frame 24 , a cranked handle 22 extending from an external surface of one of the circular plates 14 and through the frame 24 , a pair of rods 16 and a high voltage unit ( not shown ). each circular plate 14 includes four clamping mechanisms 12 , shown more clearly in fig2 and 4 , which are fully adjustable radially inwardly or outwardly across the circular plate 14 until contact is made with the sample material 10 . each clamping mechanism 12 is adjustably mounted to the circular plate 14 by a clamping plate 30 , which is attached via a nut and bolt arrangement 32 to a clamping member 34 . the clamping mechanism 12 is fully adjustable across the circular plate so as to be able to clamp sample material 10 of varying sizes ( not shown ) between the clamps 12 . the circular plates 14 are rotatable about a principal axis of rotation x using the handle 22 or other suitable mechanism . the clamped sample material 10 is , in this embodiment , an irregularly shaped brass object which is believed to have a fingerprint deposited thereon by an unknown person . the rods 16 are made of brass in this embodiment , although any suitable conductive material may be used . as shown more clearly in fig3 , each rod 16 includes a plunger contact 20 which is mounted to an end of the rod 16 by a spring 21 in this embodiment , although any suitable resilient biasing means could be used . the rods 16 are adjustably mounted to the frame 24 , say by grub screws 18 , such that they extend inwardly of the apparatus 2 toward the sample material 10 in use . this arrangement enables the rods 16 to be adjusted to ensure that the plunger contact 20 is in contact , in use , with the sample material 10 . the spring 21 enables the plunger contact 20 to adjust to and follow the contours of irregularly shaped surfaces of a sample material 10 whilst it is rotated . electric potential is provided , in use , by the high voltage unit ( not shown ), based around a brandenburg 3590 series high voltage module . the unit enables the generation of a continuously variable potential from 0 - 2 . 5 kv . other high voltage modules may be used which generate different potentials . an electrical potential of the order of 2 . 5 kv is applied through the conductive brass rods 16 . it has been observed that the higher the voltage the better the observed affect and therefore many voltages other than 2 . 5 kv will create a differential charge density sufficient to enable a latent fingerprint to be detected and identified . it should be clear to a person skilled in the art that the present invention is not limited solely to the application of a potential voltage of 2 . 5 kv and that lower or higher potentials may be applied . it will also be clear to a person skilled in the art that any suitable means of clamping the sample material securely so that it can be rotated or tilted when being examined can be used and that the present invention is not limited to only the mechanical arrangement of clamps and plates as described with reference to fig1 through 4 . for example two , three or more clamps 12 and / or other types of clamps ( not shown ) can be used . the apparatus 2 may also be used to enhance fingerprints on non - metallic ( i . e . insulating ) sample materials 10 . non - metallic objects are clamped or clampable in the same way as described with reference to fig1 through 4 above , although the rods 16 and plunger contacts 20 are removed . an electric field is then applied in the vicinity of the non - metallic sample material 10 by means of two metal , for example brass , plates ( not shown ) positioned on either side of the sample material 10 and charged with a potential of opposing polarities . it should be noted that if the substrate containing the residue also polarizes , then the differential charge density set up may not distinguish as well between the fingerprint trace where the fingerprint residue reacted with the sample and the surrounding area . nevertheless , fingerprint traces may still be resolved . when a latent fingerprint needs to be located and detected on the surface of a sample material 10 , using the apparatus as described above , at least two methods may be used to apply a conducting powder . the first method requires the introduction to the sample material 10 of ceramic spherical beads , for example of approximately 10 microns in diameter , which are coated in a fine granular (˜ 2 micron ) black conducting powder . the ceramic spherical beads are then rolled over the surface of the sample material 10 ( aided by the turning thereof ). the coated ceramic spherical beads are known in the art and are commercially available . the ceramic spherical beads act as a carrier for the conducting powder onto the sample material 10 . the beads do not themselves adhere to the sample material 10 , the conducting powder on them does . the ceramic beads are spherical so they can easily move across the surface of the sample material 10 . the conducting powder is charged when the ceramic spherical beads come into contact with the charged sample material 10 . the beads roll across the surface of the sample material 10 and the conducting powder acquires the potential of the sample material 10 . when fingerprint residue is reached , these areas have a potential difference relative to the surrounding area and the conducting powder is attracted to or repelled from this area due to electrostatic effects . on a metallic sample material 10 , the grains attract a charge equal to the charge of the metallic sample material 10 . on contact with a latent fingerprint , the lower potential of the fingerprint residue / metal corrosion attracts the grains from the beads and onto that part of the metal coincident the fingerprint residue / corrosion . in fig5 a brass sample surface is illustrated onto which a fingerprint has been deposited . the sample surface has been washed in water , acetone and then water again . the image of fig5 ( a ) has been taken five days after deposition of the latent print and fig5 ( b ) shows the ridge detail development of the same fingerprint after subsequent electrostatic enhancement using the method and apparatus of the present invention . it is shown that after using electrostatic enhancement , the fingerprint can be detected and identified whereas before , the fingerprint could not be seen . after electrostatic treatment , the conducting powder is generally vulnerable to disturbance after the electric charge has been removed . by heating the sample material 10 after treatment to a temperature of , for example 150 ° c ., the powder will bind to the sample material 10 , thereby producing a more durable sample . on a non - metallic sample material 10 , the applied electric field will polarize components within the fingerprint residue encouraging ( uncharged ) grains to be attracted to ( or repelled from ) the charge on the residue . the second method usually involves the spraying of fine granular conducting powder onto the sample material 10 by means of say an aerosol . the aerosol nozzle is charged with a potential of opposite polarity to the sample material 10 . on the metallic sample material 10 , the charged conducting powder would be attracted to the lower potential on the sample material 10 either co - incident with the fingerprint residue / corrosion or the surrounding area such that either an inverted or normal trace of the fingerprint is obtained . on a non - metallic sample material 10 , the charged conducting powder is attracted to the polarized charge on the residue of opposite polarity to the charge on the powder . it will be appreciated that the method and apparatus of the invention allows investigation of a substrate to determine whether or not a fingerprint or part thereof is present . the method is rapid insofar as the whole of the substrate need not be examined in minute detail , for example by setting up an examination array comprising a plurality of points for investigation . whilst the inventors do not wish to be limited by any theory , the mechanism for this process , when used on metallic materials , is thought to be a consequence of the corrosion on the metal surface that leads to both impurities and lattice imperfections , which will have the affect of locally increasing the resistivity of the metal at the site of the corrosion . if a potential is applied to the metal sample 10 then , under electrostatic conditions , the charge will move entirely to the outer surface with the electric field inside the metal being zero . areas of corrosion with increased resistivity will behave more like a dielectric and the charge density in these areas ( σ ′) will be less than the charge density at other parts of the surface ( σ ). using gauss &# 39 ; theorem , both the electric field and potential at a given point above the disk will be less above a corroded area . more specifically , in a section through a metal disk under electrostatic equilibrium , where a represents a gaussian surface drawn partly through the surface of the metal that has a surface area in the plane parallel to the exterior surface of the metal of a , the gaussian surface contains a charge where ε 0 = permitivity of free space and , at all points on the gaussian surface e and d a have the same direction . assuming that e has the same magnitude at all points on the gaussian surface then by the same derivation , if the gaussian surface α ′ ( taken or drawn through a corroded area ) has the same surface area a then further , as the potential difference ( δv ) between two points separated by a distance d is given by δ ⁢ ⁢ v = ∫ 0 d ⁢ e · ⅆ s the potential at a given point above gaussian surface α ′ will be less than the potential above α . it will be appreciated by those skilled in the art that various changes may be made without departing from the scope of the present invention , for example , the size and shape of the frame and clamping arms and clamping mechanism may be adjusted to accommodate sample materials of differing size or shape . it is also envisaged that other methods of applying the conducting powder would work equally well and would still produce the desired effect . also , the ceramic beads need not be used . for example a conducting powder may be applied by other means , such as dusting . it will also be understood by the skilled addressee that a detection element may be configured to be attracted to the area where the fingerprint is not or to be repelled from the area where the fingerprint , or part thereof , is deposited . the conducting powder may be any size , for example 10 microns . the metallic material may be for example , copper , steel , aluminium , brass ( as described above ) or any other suitable metallic material . the circular plates 14 may also be movable toward and away from one another to accommodate different sized and shaped articles . the method need not be practiced on an article isolated from its environment . in particular , the method may be practiced on an article in situ . for example , a potential and the detection element may applied directly to the article in situ .