Electrostatic
Vacuum Box
Safety Information
- Read all of the instructions before
using
- Keep the unit dry and clean
- Electric shock can occur
if this unit is used improperly
Description of
Equipment
- Electrostatic Vacuum Box
- Dimensions: 42.5 x 42.5 x 17.0
cm (approximately 16 3/4" x 16 3/4" x 6 3/4")
- Weight: 10 kg (22
lbs.)
- Vacuum Plate
- Corona Unit
- Developing Powder, 75 grams
- Developing Brush
- Roll of Type SP film, 40 cm x 100 meters
(approximately 15 3/4" x 328')
- Roll of Type IW film, 40 cm x 100 meters
(approximately 15 3/4" x 328')
- Adhesive Film, 25 sheets,
25 x 35 cm (approximately 9 3/4" x 13 3/4")
Background
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A. Indented
Writing
In criminal
cases where documents are present, e. g., drug transactions,
kidnap notes, bank holdup notes, forged checks, etc.,
handwriting may be present which is not visible under
normal conditions. There may have been writing which was
done on a piece of paper which left indentations in the
document in custody. The procedure in the past was to
use oblique lighting to photograph any indented writing
which may appear. This process was not always successful.
A solution
to this problem is to use electrostatic energy and black
powder. The document is placed on a vacuum plate, covered
with a sheet of plastic film, and charged with electricity.
A special black powder is brushed over the surface. The
high-voltage electric charge will cause the black powder
to collect in the indentations, making the writing easy
to see and easy to photograph. Because the original document
is covered with plastic, it is not damaged or altered.
The image of indented writing can be saved by placing
an adhesive cover sheet on the plastic film.
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B. Shoe
Print Impressions
In some burglary
cases, suspects enter the business or residence by coming
in through a wall or the roof. As they proceed to ransack
the building, they may toss papers on the floor and then
step on them. Unfortunately, the shoe print impressions
left on these papers are in a very light dust on manila
file folders, on newspapers or on other documents with
writing on them. Photographing these faint images on light-colored
or printed papers will not reveal a clear image of the
shoe print impression.
Using the
same electrostatic energy as used for the indented writing
application, the shoe print impressions in dust can be
transferred from the paper documents to a plastic sheet.
A dark background can be utilized to photograph the smallest
details of these recovered shoe print impressions.
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B. Directions
for Operation - Shoeprints on Paper
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1. Place the
paper on top of the vacuum box (without the special vacuum
plate) and cover it with the Type SP (thicker of the two
films) plastic film. Switch on the fan to eliminate any
air gaps. For newspaper and other relatively smooth papers,
use the fan setting on "low." For wrinkled or heavy paper,
try the fan setting on "high." Cut the film from the roll.
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2. Plug the
wire from the Corona unit into the matching colored socket
on the vacuum box. Turn on the Corona switch. Holding
the Corona unit about one-half inch above the paper, pass
it back and forth over the film for 10 to 15 seconds.
Pass the center of the Corona unit over all areas of the
paper.
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3. Turn off
the fan and remove the paper with the film still on it.
Holding the paper and the film "sandwich," flip it over
and place it on the glass plate of the camera setup. Remove
the paper. The shoeprint will be on the clear plastic
film.
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4. Hold a
light at a low angle to see the shoeprint impressions.
Photograph recovered prints with darkfield-lighting. (See
the description of darkfield-lighting below.)
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Photography of
Shoeprints with Darkfield-Lighting
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1. Using a
copy stand camera, place the film face down on a glass
plate and remove the paper document. Suspend the glass
plate about 2-3 feet above a black background.
2. Direct
the lights up to shine on the glass plate from below.
Experiment with the number and position of the lamps.
Use a medium-contrast to high-contrast film. Note: the
resulting image will be reversed left to right.
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Helpful Hints
- If the paper evidence in the case of
either indented writing or shoeprint impression recovery is
also going to be examined for latent prints, perform the indented
writing or shoeprint impression recovery first. Processes
like Ninhydrin or Physical Developer are wet processes which
will destroy indented writing or shoeprint impressions in
dust.
- When applying the developer powder
to the film in indented writing recovery, apply it in long
strokes, first side to side, then top to bottom. Apply small
amounts of powder. More can be added. Too much cannot be taken
away easily.
- When recovering shoeprints from regular
paper or thin paper, use the fan setting on "low." However,
if the paper is heavier or is wrinkled, it may be necessary
to turn the fan on the "high" setting to smooth out the paper
and obtain complete contact between the paper and the film.
- Only the center of the
Corona unit is active. Use the center of the Corona unit to
charge the film and paper. When passing the Corona unit over
the film, it is easy to miss the edges and corners of paper,
so be certain that the active area of the Corona unit passes
over the entire surface of the paper. Do not set the Corona
unit down on top of the film and paper while processing, as
it will produce a dark area of powder if using it for indented
writing.
Handling and Storage
of Film After Lifting a Shoeprint Impression
- The dust adhering to the plastic film
is not permanent. The footwear impression should be photographed
as soon as possible. Keep the film from coming into contact
with other surfaces and rubbing the dust off while moving
it to the camera or transporting it to the photo studio. Tape
it to a large piece of cardboard or place it in a shallow
box. It is recommended to carry the sheets flat at all times.
- Do not roll up the used film and put
it in a mailing tube. Do not wrap it in plastic or place it
in a plastic bag. If this is done, a partial transfer of the
footwear impression to the plastic wrapping material may occur.
- In some legal jurisdictions, the film
may be destroyed after the image is photographed. Check with
your district attorney for a legal opinion. Otherwise, long-term
storage can be accomplished by the taping the edges of the
film into a shallow box, like an empty photographic paper
box or pizza box (which can look rather unprofessional if
the item is taken to court) or in a specially-designed footwear
cast/lift film box. The lifted footwear impression on the
film should be photographed as soon as possible, however,
as even long-term storage of the impression in this manner
is not permanent.
- Stacking more than one
piece of lift film with impressions on them inside of an empty
photographic paper box is not recommended. The impressions
may transfer or may be rubbed off. Our special cast/lift film
boxes come with an insert which gives an additional layer
of cardboard to which the tape the lift film can be attached.
It is supported above the first lift film so that both layers
of film are protected from rubbing the insides of the box
and each other.
Photography Tips
- When photographing any shoe impression,
it is imperative to have a scale in the picture. By placing
a transparent ruler face down in the photograph, the numbers
will read backwards. By turning the negative over when placing
it in the enlarger to make a print, the numbers on the scale
will read correctly and the shoe impression will be in the
proper orientation for comparison.
- When taking the photograph with darkfield-lighting
or backlighting, the case number and other information can
be written on a piece of thin, white paper. Place this paper
upside down and the light will shine through it. When printing
the negative, turn or rotate the negative in the enlarger
so the case number information shows correctly.
- For photography of either shoeprint
impressions or indented writing, a medium-contrast to high-contrast
film should be used. Do not use color films, as they do not
show contrast as well as black-and-white films.
- While small-format film
in 35mm cameras can be used, medium- to large-format cameras
are recommended. The Polaroid MP-4 or MP-4 Plus or other style
of copy stand large-format film cameras use 4 x 5 sheet film
and have methods for controlling the amount and direction
of the light.
Care and Maintenance
of the Equipment
- Keep the powder from being drawn into
the vacuum.
- Do not touch the wire
inside the Corona Unit. It is very fragile and can break.
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