Gel Lifting of Footwear Impression Evidence

Topics - Gel Lifting of Footwear Impression Evidence

Overview - Gel Lifting

Photography of Gel Lifters

Helpful Suggestions

Articles - Gel Lifting

The C.A.S.T. Website wishes to thank BVDA International bv for their permission to use gelatin lifting information included in their 'Manual of Use for BVDA Lifters' in the creation of this Webpage.

Overview - Gel Lifting of Footwear Impression Evidence

Gel lifters contain a thick, non-aggressive, low-adhesive gelatin layer that permits the lifting of traces from almost every surface, including porous material such as paper or cardboard. Lifted impressions can be taken along for photography or closer examination.

Each kind of lifter can be cut to size using scissors, and, can be marked with the appropriate case information. All lifters are protected by a cover of transparent polyester film.

Categories of Gel Lifters:

• Black lifters.
• White lifters.
• Transparent lifters.

Photography of Gelatin Lifters

Prints can be photographed with reproduction lighting in a dark room. The oblique lighting (from a film spot at at 45 degree angle) should come from one side. The film of the camera has to be parallel to the lifter. All reflections should be avoided, therefore photography should be done in a totally dark room. To avoid reflections, the camera should be shielded from the light source ( e.g. with black cardboard). Next to the lifter, a ruler should be present, together with case information. Before photogrpahy is done, the cover sheet has to be removed. To avoid contamination, care should be taken to work in a dust-free room.

Footprints (dust marks) on black lifters are the most difficult to photograph. To find the correct lighting, a set of photographs with different shutter speeds ( usually diaphragm 11 is taken as a standard ), of a dust print should be made to establish a standard. Due to the extreme black of the foil, heavy over-exposure is possible, thereby enabling the reproduction of even very weak traces. Once the standard is set, the camera can be adjusted to the effective film sensitivity ( a 125 ASA film can for example be found to have an effective fim sensitivity of 32 ASA ).

With weak traces ( weaker than the standard ), longer shutter times are necessary. With powdered footprints, much more light is reflected towards the camera. Therefore, shorter exposure times have to be used.

For reproduction of all the details in dust prints, the weakest details (or the part farthest away from the spot), should be the criterium for the exposure time. Relative over-exposure of other parts is corrected in the paper printing process. To be certain that a good reproduction is made, a cascade of three exposures is normally taken. Due to the oblique lighting, the side of the lifter closest to the lamp receives more light than the opposite side. Therefore, it is advisable to put the side of the lifter with the weakest details closest to the light source.

Helpful Suggestions for the Gel Lifting of Footwear Impressions

*   Let the Gelatin Lifter Absorb the Impression  
Research has recommended to allow the lifter to remain on the footwear impression for about ten (10) minutes, prior to lifting/recovering. This allows sufficient time for the impression to completely transfer to the lifter.

*   Effective temperature range 
The lifters should certainly not be left in sunlit areas, but kept in shaded areas. The gelatin layer will begin to melt above 40 ° centigrade ( 104 ° fahrenheit). In very hot climates it may be necessary to use a cool box. The lifters can be used at freezing temperatures, although removal of the cover sheet may present a problem. Problems can be circumvented by keeping the lifters in a warmer area prior to use. Lifting, without problems, at temperatures as low as -15 ° Centigrade ( 5 ° Fahrenheit) has been reported.

*   Storage 
Lifters are normally stored at room temperature. The black and the white lifters have no known shelf life. The transparent lifters slowly develop a brown tint, due to a chemical reaction between the gelatin and added ingredients. Therefore, it is preferable to store transparent lifters in a refrigerator. Avoid prolonged storage in humid environments.

*   Double lifting 
Often, a print can be lifted twice. The second lift will, in many cases be much clearer, but with less contrast. Another possibility is lifting for a second time after additional dusting with fingerprint powder.

*   Air Bubbles 
Avoid trapping air bubbles on the lifter by using a clean roller. Trapping of air bubbles will result in the creation of shallow craters, which will not destroy the print, but may cause problems in photography.

*   Impressions in Course Material 
When footprints contain very course material (sand), problems can be expected in replacing the cover sheet. Around the course particles, small air bubbles will be present. When too many are present, the cover sheet cannot sufficiently be replaced unto the lifter. It is recommended to photograph the footprint before lifting is done. Also, the lifted print can be photographed at the crime scene before the cover sheet is replaced. Finally, the lifter can be secured to the bottom of a cardboard box, without replacing the cover sheet on the lifter.

Footwear Textbooks Containing Gel Lifting

Articles - Gel Lifting of Footwear Impression Evidence:

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