Technical Note

Aqueous Amido Black

Introduction

Aqueous Amido Black is a protein dye solution, sensitive to the proteins in blood and other substances. It will stain the protein residue in a blood-contaminated latent print and turn a blue-black color. It will not stain the normal constituents found in latent print residue so it should only be used in the case of blood-contaminated latent prints to be successful. Using this solution is not a presumptive or conclusive test for blood as it may react with other proteins not specific to blood.

Safety

As with all chemicals, always read the MSDS (material safety data sheet) to learn about the safe handling and health hazards of each chemical. Nitrile or chemical gloves and protective clothing, such as disposable, TyvekŪ lab coats or coveralls, should be worn when using Aqueous Amido Black. It should be used in a fume hood whenever possible or with an organic/acid respirator at the crime scene. Some of the solvents used to mix it are hazardous and/or corrosive. Use the proper safety precautions in handling and disposal. Because this solution is used on surfaces contaminated with blood, the proper safety precautions for disposal of biohazards must be considered.

Processing Instructions

Prior to applying Aqueous Amido Black, it is recommended to do a presumptive test for blood and to collect a sample of the suspected blood for DNA or other blood-type testing. Aqueous Amido Black can be applied to any nonporous surface, such as metal, plastics or glass. However, since Aqueous Amido Black is a corrosive solution, it will begin to damage metal surfaces, such as handguns, knives and rifles if not washed off. Aqueous Amido Black is best applied by either submersion or by washing the solution over the surface in question. It is NOT recommended to spray Aqueous Amido Black. Leave the solution on for 1 to 3 minutes and then rinse off with distilled water. It can be repeated, but observe it for overdevelopment.

Processing Instructions - Vertical Surfaces

Tape or affix a length of non-textured paper towel material over the wall or other vertical surface. (A textured paper towel will leave its pattern in the latent print. ) Wash the Aqueous Amido Black solution over the paper towel, allowing it to make contact with the vertical surface. After about 1 to 3 minutes, remove the paper towel and rinse the vertical surface with distilled water. Use caution with some plaster and stucco walls, the solution may stain the entire surface.

Processing Instructions - Horizontal Surfaces

Aqueous Amido Black solution can be washed directly on the floor or other horizontal surface. Use non-textured paper towel material to blot up the excess solution. After about 1 to 3 minutes, rinse with distilled water and blot with non-textured paper towel material. If working on a floor surface, be aware that some floor waxes may react with the solution and cause background staining.

Sequential Processing

The first process suggested is to use fluorescent powders (choose the color most appropriate for the background fluorescence). Then use Aqueous Amido Black and then, Physical Developer. It is suggested to photograph any latent prints developed with each process before treating the evidence with a new process. The Physical Developer may or may not enhance the bloody latent prints, but it may develop other latent prints.

Photography

Photography of latent prints developed with Amido Black should not pose any problems if the surface background is a light color. If the surface is a dark color but will fluoresce, it may be beneficial to use fluorescence examination to enhance the photographic contrast. One recommended method is to use a Forensic Light Source set between 550 and 600 nm, view with red goggles and photograph with a dark red filter, such as a Tiffin or Wratten 25 or 29.

Storage and Shelf-life

Aqueous Amido Black solution has a shelf-life of at least one year. It should not be subjected to extreme cold or hot temperatures. It is not necessary to store this solution in a refrigerator. Storing it at room temperature within an office situation is adequate.

Disposal and Cleanup

Aqueous Amido Black solution is classified as hazardous because it is corrosive. Since any crime scene or piece of evidence is suspected to have blood on it when used with this solution, the greater hazard of the blood dictates its disposal and cleanup. Clean any surfaces in accordance with the regulations for cleaning the biohazard of blood.

Additional Reading

Advances in Fingerprint Technology edited by Dr. Henry Lee and Dr. R. E. Gaensslen
Friction Ridge Skin: Comparison and Identification of Fingerprints by James F. Cowger
Manual of Fingerprint Development Techniques by the British Home Office, 2nd edition

Ordering Information

Catalog No. 1-2740 Aqueous Amido Black, one liter
Catalog No. 1-2741 Aqueous Amido Black, one gallon
Catalog No. 8-5008 COWGER/Friction Ridge Skin
Catalog No. 8-5015 HOME OFFICE/Manual of Fingerprint Development Techniques, 2nd edition
Catalog No. 8-5041 LEE/Advances in Fingerprint Technology
   

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