Lifting cyanoacrylate developed fingerprints
The black Gellifters can be used to lift fingerprints which are developed with cyanoacrylate (an example in a pop-up window). These lifters are a last resort where:
- a developed fingerprint is stained with a staining solution and the object seems to fluoresce in the same range as the dye;
- an object is contaminated and the contamination also absorbs the staining solution, thereby causing a loss of contrast between the print and background;
- a fingerprint is overdeveloped, or
- an object is partly porous and partly non-porous, e.g. a plastic bottle with a paper label.
Due to the extreme sensitivity of the black gelatin layer
of the lifters, a fingerprint is easily copied onto the lifter by applying the
lifter over the developed fingerprint. After removing the lifter, the fingerprint
on the lifter can easily be viewed and photographed using coaxial lighting (as
described in the section, "Indented writing").
Often the photographs produced after lifting a print with a black Gellifter are better and sharper than the same print photographed in fluorescence.
Hint: the second lift of the same fingerprint is often even better, because the first lift removes most of the background.
Lifting untreated fingerprints
Even fingerprints that have not been treated with powders or cyanoacrylate can be lifted with black Gellifters (example in a pop-up window). An object on which prints are suspected, but which is difficult to treat (for example a plastic surface) can be searched for prints by applying a black Gellifter. Due to the extreme sensitivity of the black gelatin layer of the lifters, a fingerprint is easily copied onto the lifter by applying the lifter over the untreated fingerprint. Another example is a strong print that is already visible with the naked eye. To retain the perfect detail that these prints can have, they could be lifted before powdering is done.
Viewing and photographing these kinds of lifted prints is done in the way described under the heading "Indented writing": almost coaxial lighting.
Special Techniques for Lifting Fingerprints
Often, a print developed with fingerprint powder can be lifted twice. The second lift will in many cases be much clearer, although it will have less contrast. Another possibility is lifting for a second time after additional dusting.
Of course no rules can be given for these techniques, as much depends on experience. However, this is recommended for fingerprints on aluminium.
Improving older fingerprints
on objects which have been standing in sunlight or outside for longer periods
are difficult to render visible. Because all the moisture has evaporated from
the print, it hardly absorbs any powder. By attaching a piece of Gellifter to
it for some minutes, the print can be rehumidified. Subsequently, the print can
be dusted in the usual way and lifted with a fresh piece of Gellifter. Before
using this method, ensure that the object in question has cooled down.
These are usually prints where the sole of the shoe acts as a stamp on the surface, thereby leaving an invisible print or one which is barely visible. The surfaces from which shoeprints can be lifted using BVDA Gellifters, are all smooth, hard surfaces such as floors, painted wood, paper, table-tops etc. For lifting shoeprints (dust marks), the large black Gellifters B-12000 (13x36 cm / 5.2x14.4") and B-12500 (18x36 cm / 7.2x14.4") are commonly used.
Footwear impressions that are not visible to the naked
eye can be found in a number of ways. The best known method is to use a torch
or floodlight at a low angle (using a mirror works best.) Because shoeprints that are not even visible using
low angle lighting, can be seen once they have been lifted with black Gellifters,
another method is to cover the whole area where shoeprints are suspected, with
Gellifters. We even supply extra large Gellifters 36x50 cm / 14.4x20") for
this purpose. When the entire area is covered with Gellifters, reconstruction
of the pattern is facilitated by drawing stripes over the seams of the Gellifters.
Before picking up the Gellifters, it may be advantageous to let them lie on the
surface for some minutes, so as to humidify the print.
Another method of searching for shoeprints that should
be mentioned, is the use of electrostatic lifting.
Since electrostatic lifting leaves more than enough residue for subsequent lifting
with a Gellifter, it can be used before gel lifting. Because electrostatic lifting
also removes a lot of background dust, usually even better lifts are obtained
with the Gellifter afterwards rather than using the latter on its own.
The procedure for applying the Gellifters is the same as that used to lift fingerprints
Even if shoeprints do not show up when lighting the surface and are not visible after lifting, they may become apparent when obliquely lighting the surface of the Gellifter in a dark room (after removing the cover sheet). Gellifters with no apparent prints in normal light, now show a highly detailed image. After photography, the cover sheet can be replaced following careful cleaning. A large roller is very convenient when replacing the cover sheet on these large Gellifters, so as to avoid trapping air bubbles.
Shoeprints which have been rendered visible with fingerprint powders, such as Magnetic Jet Black or Silver Special, can also be lifted with BVDA Gellifters. The color of the Gellifter used depends on the color of the fingerprint powder, e.g. a white lifter for dark color powder and a black lifter for light color powder.
WARNING: Avoid contamination of the Gellifters once the cover sheet has been removed. We recommend wearing dust-free clothing when handling and photographing the Gellifters.
Longevity of lifted shoeprints
Lifted shoeprints (dust marks) may slowly fade in time. For very weak prints this may be noticeable after storing them for a few days. This will depend on the temperature. The lower the temperature, the slower they will fade. This, however, should not be a concern, since lifted shoeprints can easily be photographed after removing the cover sheet. Oblique lighting will show details which are not visible before photography. So far, we know of no materials that fade on the Gellifter surface before adequate photographs have been taken.
For best results you should not replace the cover sheet. Transportation of the lifted print is of course more difficult then. We suggest using double-sided adhesive tape and a clean, shallow cardboard box, like the ones that photographic paper comes in.
When shoeprints contain very coarse material, e.g. sand, you may expect difficulties when replacing the cover sheet. Small air bubbles are likely to collect around coarse particles. If too many are present, the cover sheet will not adhere properly to the Gellifter. Several measures can be taken to avoid these problems. First of all, it may be advisable to photograph the shoeprint before lifting it. Secondly, the lifted print can be photographed on the crime scene before the cover sheet is replaced. Thirdly, instead of replacing the cover sheet, the Gellifter can be put in a clean box (e.g. a photographic paper box) and taped to the bottom. Fourthly, the cover sheet can be secured to the Gellifter with staples or adhesive tape, to prevent movement which would allow the coarse particles to destroy characteristic details.
Prints can easily be photographed with reproduction lighting in a dark room. The oblique lighting (from e.g. a film spot at a 45° angle) should come from one side. The film of the camera has to be parallel to the Gellifter. All reflections should be avoided, therefore photographing 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 Gellifter, a ruler should be present, together with a case number or the like. Before photographing the print, the cover sheet must be removed. To avoid contamination, care should be taken to work in a dust-free environment (e.g. no smoking while photographing).
Shoeprints (dust marks) on black Gellifters are the most difficult to photograph. To establish the correct level of lighting, you should take a set of photographs at different shutter speeds (usually diaphragm 11 is taken as a standard) of a test print (dust print) to establish a standard for the mounting you use. Due to the extreme black of the foil, substantial overexposure is possible, thereby enabling the reproduction of even very weak traces. Once the standard is set, the camera can be adjusted to the film sensitivity you have established as being effective (a 125 ASA film can for example be found to have an effective film sensitivity of 32 ASA). Where traces are poor (poorer than the standard), longer shutter times are necessary.
In the case of powdered shoeprints, much more light is reflected towards the camera. Therefore, shorter exposure times need to be used. The same holds for lifted (powdered) fingerprints. For reproduction of all the details in dust prints, the weakest ones (or the part farthest away from the spot) should provide the criterion for the exposure time. Relative overexposure of other parts is corrected in printing. 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 a Gellifter closest to the lamp receives more light than the other side. Therefore, it is advisable to put the side of the Gellifter with the weakest details closest to the light source.
Following the abovementioned procedures, the normal grades of photographic paper ordinarily suffice in printing. Overexposure of, e.g. the side of the Gellifter closest to the light source, is corrected when printing the negative.
When paint left on a car by a hit-and-run driver has to be removed for examination,
the white Gellifters can be used. After removing the cover sheet, adhere one edge
of the Gellifter to the surface of the car directly under the spot containing
the paint which is to be removed. Now scrape off this paint carefully with a scalpel.
The material you remove, will fall into the gap between the Gellifter and the
surface of the car, or onto the Gellifter itself. When enough material has been
removed, adhere the entire Gellifter to the surface of the car and rub it firmly
all over. This way, all loose particles will adhere to the Gellifter. The Gellifter
can then be removed and the cover sheet replaced. If necessary, the cover can
be secured with staples or adhesive tape.
Taking Samples of Micro Traces
Due to the non-aggressive nature of the Gellifter, samples
of micro traces and hair can be taken without fear of damaging the material. If
it is necessary to remove micro traces from the Gellifter, the low tack facilitates
their removal with the use of a scalpel or suitable pair of tweezers. Hair samples
are taken with white Gellifters.
If an area is to be searched for micro traces, we recommend dividing it into squares (e.g. 20x20 cm, approximately 8x8 inches) and using a fresh piece of Gellifter for each square. The size of the Gellifter is actually dictated by the amount of contamination in the area to be investigated, since taking samples of dirt or large amounts of micro traces will result in a rapid loss of tack. A size of 8x8 cm (approximately 3x3 inches) usually suffices.
Bullet Holes in Window-panes
containing bullet holes have a very specific pattern of cracks around the hole.
After collecting residue around the hole, it is standard procedure to photograph
it. However, this can be difficult due to reflections, a disturbing background
or light sources. If this occurs, the hole and its surroundings can be powdered
with Silver Special Powder (after the residue around the hole has been secured!).
The image can then be transferred to one or several pieces of Gellifter.
Blood stains can be lifted by using white Gellifters, for example. These are left for one or more minutes on the stain (to humidify) before they are picked up.
WARNING: Since gelatin is a protein, it will no longer be possible to analyse a stain once it has been lifted. Gelatin will interfere with the analysis of protein present in blood!
Photographing blood stains is the preferred method. On a non-absorbent surface, most prints will improve with chemical enhancement. In many situations, the treated print can still be lifted after chemical enhancement and photography. Lifting the stained print with a white Gellifter eliminates any background interference (example in a pop-up window). The print must be photographed soon after it has been lifted (preferably less than one hour), as the dye from the enhanced print will diffuse across and into the gelatin layer of the Gellifter. This will not be noticeable until a couple of hours after the lift. The diffusion is irreversible and continues even in freezing temperatures. The Gellifter can therefore not be stored.
Lifting procedure: apply the white Gellifter carefully in order to avoid trapping air bubbles which could result in an incomplete transfer. Leave the Gellifter on the print for at least a couple of minutes to half an hour.
Suitable treatments which can be followed by lifting, include:
Note: Diaminobenzidine (DAB) will not transfer.
- Amido Black (methanol and water based)
- Leuco Crystalviolet (LCV)
- Crowle's stain
- Coomassie Blue
- Hungarian Red
Fluorescence: The use of Hungarian Red has one further
advantage. The lifted print strongly fluoresces on a white Gellifter under green
in a pop-up window). A red barrier filter is used for viewing and photographing