For the lifting of footwear impressions (made with dust or dirt) no material is better suited than black gelatin lifters, due to its low tack. Whereas synthetic materials with a high tack tend to lock in air bubbles upon application, a black gelatin lifter easily lifts a complete print without disturbing the surface on which the print is found.
Furthermore, the high-gloss black gelatin layer absorbs light so strongly that it can be over-exposed many times. When a black object, next to the lifter, shows up white on a photograph, the lifter is still dark gray. Its light absorption enables photographing of even very faint impressions.
Apart from being available in several sizes, the (black and white) lifters are also available with different backing materials: rubber (on which notes are easily made) and polyester (a little less flexible). The shoeprint sizes are either 5.2" (13 cm) or 7.2" (18 cm) wide and 14.4" (36 cm) long. Also available are sheets of 14.2 x 17.7 inch (36 x 45 cm).
In some countries, transparent lifters are used for lifting footwear impressions. These are then photographed with a dark-field method.
White gelatin lifters are not intended for the lifting of footwear impressions in dust (black lifters give a much better contrast) but are well suited for the lifting of prints in blood (finger- or shoeprints) that have been stained with protein dyes, such as Amido Black or Hungarian Red. For an example see this (pop-up window).
Also, shoeprints made with muddy shoes on non-absorbing surfaces, which have been stained with an aqueous solution of Safranine O (1 g/liter), can be lifted with white gelatin lifters. The fluorescence of Safranine O (using green light and red camera filter) is then photographed (poster of M.J.M. Velders at the IAI conference in Danvers/MA/USA; 1997).
All gelatin lifters are packaged in sealed envelopes made of a laminate material. This material protects the gelatin layer against moisture. Thus the tack is retained, even after prolonged storage.