Amido Black
Introduction
Amido Black, also known
as Naphthalene Blue-Black or Naphthalene Black 12B, is a protein
dye, sensitive to the protein in blood. 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.
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. Gloves
and protective clothing should be worn when using Amido Black.
It should be mixed and used in a fume hood or with an appropriate
respirator. Amido Black is not a carcinogen. Some of the solvents
used to mix it are hazardous and/or flammable. Use the proper
safety precautions in handling and disposal.
Mixing Instructions
Working Solution
- 1 gram Amido Black
- 50 ml Glacial Acetic Acid
- 450 ml Methanol
Weigh out 1 gram of Amido
Black and place it in a one liter glass beaker. Place it on
a magnetic stirrer. Add 50 ml of Glacial Acetic Acid and stir.
When completely mixed, add 450 ml of Methanol and stir for at
least 30 minutes. When completely mixed, store the solution
in a glass bottle. Properly label the bottle.
Glacial Acetic Acid-Methanol
Solution
- 100 ml Glacial Acetic Acid
- 900 ml Methanol
Pour 100 ml of Glacial
Acetic Acid into a glass storage bottle. Add 900 ml of Methanol.
Stir the solution until mixed. Properly label the bottle.
Glacial Acetic Acid-Distilled
Water Solution
- 50 ml Glacial Acetic Acid
- 950 ml Distilled Water
Pour 50 ml of Glacial Acetic
Acid into a glass storage bottle. Add 950 ml of Distilled Water.
Stir the solution until mixed. Properly label the bottle.
Processing Instructions
Step One: Fix the blood
on the surface of the evidence.
- Pour enough methanol to cover the item
of evidence into a clean, glass tray.
- Immerse the evidence in the methanol
for about one hour.
- Cover the tray to prevent evaporation.
Replenish the methanol in the tray, if necessary.
- Discard the methanol after use.
- If the evidence cannot be immersed
in methanol, heat the surface with a lamp, heater or oven
for at least one hour. Be careful of the risk of fire.
Step Two: Using the working
solution.
- Pour enough working solution to cover
the item of evidence into a clean, glass tray.
- Soak the evidence in the working solution
for about two to three minutes or until the latent prints
become a blue-black color.
- If the solution in the tray becomes
heavily contaminated, it should be replaced with fresh solution.
- If the solution is not badly contaminated,
it can be poured back into the bottle and used again.
Step Three: First rinse
- Pour enough Glacial Acetic Acid-Methanol
solution to cover the item of evidence into a clean, glass
tray.
- Immerse the evidence into the solution
and rock the tray gently.
- When excess dye has been removed from
the background, take the evidence out of the rinse.
- If the solution in the tray becomes
heavily contaminated, it should be replaced with fresh solution.
- Discard after use.
Step Four: Second rinse
- Pour enough Glacial Acetic Acid-Distilled
Water solution to cover the item of evidence into a clean,
glass tray.
- Immerse the evidence into the solution
and rock the tray gently for about 30 seconds.
- If the solution in the tray becomes
heavily contaminated, it should be replaced with fresh solution.
- Discard after use.
Step Five: Drying and Photographing
- Allow the evidence to dry at room temperature.
- Photograph any useful latent prints.
Sequential Processing
Treatment with Physical
Developer may be done after Amido Black to try to improve the
developed latent prints. It is suggested to photograph any latent
prints developed with Amido Black before treating the evidence
with Physical Developer.
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.
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