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Technical Note
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
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. |
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. |
A. Directions for Operation - Indented Writing |  |
1. Place the special vacuum plate on top of the vacuum box. Plug the vacuum pipe and the ground wire into the vacuum plate and vacuum box, matching the colors to the colored sockets.
(NOTE: In these illustrations, the pipe and ground wire are shown coming out of the side of the vacuum plate. In the older versions of the instrument, they come out of the front of the vacuum plate.)
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2. Place the document face up on top of the vacuum plate. Use tweezers to handle the document. Your fresh latent prints may develop. |
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3. Using the Type IW (thinner of the two films) plastic film, cover the document and vacuum plate. Turn on the fan to create a partial vacuum. |
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4. Using a cotton ball or a small piece of cloth, smooth the film over the document to eliminate any wrinkles or air gaps. When the film is smooth, switch on the vacuum pump and cut off the film from the roll. |
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5. 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 document, pass it back and forth over the film for 10 to 15 seconds. Pass the center of the Corona unit over all parts of the document. |
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6. Using the developing brush, gently apply the developing powder to the plastic film. Brush back and forth (top to bottom and left to right), applying powder as necessary to develop each word.
HINT: Use the least amount of powder necessary to develop the image. Practice and experience will guide you. When you see partial text, concentrate on that area and use more powder on that area, if necessary. |
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| 7. To save the visible indented writing, cover the plastic film with an adhesive sheet. Start the adhesive film at one end of the film to cover it. Or allow the adhesive film to sag and stick to the middle of the film to cover it from the middle to the edges. For good adhesion, rub the surface with a roller. Turn off the fan and vacuum pump. |
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8. This procedure does not alter your original document. If you overdevelop an image, or have an image and accidentally wipe it away, or have a wrinkle in the film -no problem- just start over again with a new length of film. |
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B. Directions for Operation - Shoeprints on Paper |
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. |
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. |
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. |
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.) |
Photography of Shoeprints with Darkfield-Lighting | |
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.
Replacement Supplies
Catalog No. 4-5526 Type SP Film, 100 m roll
Catalog No. 4-5527 Type IW Film, 100 m roll
Catalog No. 4-5528 Developing Powder, 75 grams
Catalog No. 4-5529 Adhesive Sheets, 25 sheets
Catalog No. 3-3015 Cast/Lift Film Box (17 1/4" x 11" x 2 1/4"), 25 boxes
Introduction
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The goal of latent print examiners and technicians is to discover and
collect latent prints by various means. The ultimate goal is
to identify those latent prints to the person responsible
for the criminal act and prosecute them to the fullest
extent of the law. Some of these means to develop latent
prints include processing evidence and other surfaces using
powders, chemicals and lighting techniques. The purpose of
this booklet is to provide a resource of information about
latent print processing techniques. This booklet does not
contain every process available and does not claim to be all
inclusive of all variations of processes. The information
has been collected from various sources.
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Caution
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This booklet
contains descriptions of processes utilizing chemicals or
combinations of chemicals which may be hazardous to the
user's health. It is strongly recommended that proper
precautions be taken when using hazardous chemicals or
combinations thereof. Safety equipment needed may include
fume hoods, gloves, protective clothing, safety goggles,
splash shields or respirators. It may be necessary to store
these chemicals in specific containers or cabinets. It is
the user's responsibility to know and use the proper and
adequate safety equipment required the various chemicals
listed.
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Disclaimer
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Lightning Powder
Company, Inc. assumes no responsibility for the use or
misuse of any of the chemicals, procedures, methods of ideas
described herein resulting in injury and/or damage to
persons or property.
Copyright © 2005 Lightning Powder Company,
Inc.
The material contained in and displayed by this Web site may be reproduced
with acknowledgment of its source.
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