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Powder suspensions

Available ready-for-use or as components

Ready-for-use black and white powder suspensions are available to develop finger marks on non-porous, semi-porous and the adhesive sides of tapes for example.
 
Also the required components to prepare your own suspensions are available as well as convenient kits which contain the required materials.
 

Suspension Powder Silver/Grey

Suspension Powder Silver/Grey was originally marketed as Sticky-Side powder. As the name already indicates this powder is meant to be mixed to a suspension used to develop finger marks on the sticky side of tapes.
 
Suspension powder Silver/Grey is an aluminium based powder. The powder should be mixed with a solution containing a detergent like Dactyflo and water. The paint like suspension is applied to the surface using a soft brush.
 
The silver/grey suspension is most effective on the adhesive side of dark and light coloured tapes, labels and other adhesive surfaces.
 

Fingerprint developed with suspension powder silver/grey on blue electrical insulation tape
Fingerprint developed with suspension powder silver/grey on yellow electrical insulation tape
Fingerprint developed with suspension powder silver/grey on red electrical insulation tape
 

Suspension Powder Black

Suspension Powder Black is a fine black powder and is available as an iron oxide based as well as a carbon based version. The powder should be mixed with a solution containing a detergent like Dactyflo and water. The paint like suspension is applied to the surface using a soft brush.
 
The iron oxide based suspension is most effective on light coloured non-porous and semi-porous surface.
 
The carbon based suspension is most effective on non-porous adhesive sufaces.
Product
 

Suspension Powder White

Suspension Powder White is a titanium dioxide based powder. The powder should be mixed with a solution containing a detergent like Dactyflo and water. The paint like suspension is applied to the surface using a soft brush.
 
The white suspension is most effective on dark coloured non-porous and semi-porous surface as well as on the adhesive side of dark coloured tapes, labels and other adhesive surfaces.
Product
 

Wet Powder black

Wet Powder Black is a similar product to Suspension Powder Black however this is pre-mixed with detergent so ready-to-use.
 
It is applied to the adhesive side of a tape with a fingerprint brush by "painting" the surface and then rinsing the excess off with tap water after leaving it on the tape for 10 to 15 seconds. Wet Powder Black is a carbon based powder suspension.
 

Wet Powder white

Wet Powder White is a similar product to Suspension Powder White however this is pre-mixed with detergent so ready-to-use.
 
It is applied to the adhesive side of a tape with a fingerprint brush by "painting" the surface and then rinsing the excess off with tap water after leaving it on the tape for 10 to 15 seconds. Wet Powder White is based on titanium dioxide.
 

Tape Release Agents

Before the adhesive side of tapes can be treated for fingerprints or sampled for DNA traces it will first need to be removed from the surface to which it is stuck. A number of methodes are used for this. One physical method relies on the fact that the adhesives used on tapes lose their rubber-like properties when the temperature is lowered enough. Putting the evidence in a freezer is one method that sometimes works. Locally cooling the tape with freezer spray (used in electronics) is another. For tapes on paper a tray with liquid nitrogen can be used.
 
On smooth surfaces removing a tape can be aided by heating the tape with a heat gun.
 
In the past when the adhesive-side of tape was based on cellulose ("Sellotape"), acetone and hexane were used for removing tape from paper. With modern pressure sensitive adhesive tapes more identifiable fingerprints are recovered with "Turkish solvent" or the older release agent based on a xylene substitute used in microscopy to which 5% chloroform or (less toxic) dichloromethane is added (Journal of Forensic Sciences, 1990, Vol. 35, No. 6, pp. 1373-1383; [doi:10.1520/JFS12973J]; in which a method to unravel tape stuck adhesive side to adhesive side is described).
Heptane (the ingredient of Un-Du label remover) is also used.
 
"Turkish solvent" was popularized in the beginning of this century by Uwe Amerkamp from the BKA who visited collegues in Ankara, Turkey and noticed the good results they got using a mixture of cyclohexane and isopropanol (1:2) as tape release agent.
The xylene subsitute is a mixture of aliphatic hydrocarbons ("hydrotreated heavy naphtha") so chemically similar to hexane and heptane although this mixture has a higher boiling point.