Gentian Violet, also known as Crystal Violet, is a triarylmethane dye that's been a staple in forensic science for well over a century. It's a deep purple, almost blue, solution. Why do we use it? Gentian Violet has a strong affinity for the fatty and oily components found within fingerprint residue. When it reacts with these components, it forms an intensely colored purple stain, making latent prints clearly visible, especially on non-porous, adhesive surfaces.
Equipment
Using Gentian Violet is straightforward. Here's your equipment checklist:
- Shallow Tray or Dish: A non-reactive glass or plastic tray large enough for submerging items.
- Gentian Violet Solution: Naturally! (Details below)
- Distilled Water: For rinsing.
- Tongs or Forceps: For handling items without contamination.
- Personal Protective Equipment: Lab coat, nitrile gloves, safety glasses.
Ingredients for a 1-Liter Gentian Violet Solution
- Gentian Violet Powder: 1 gram
- Distilled Water: 1 liter (1000 mL)
Mixing Procedure
- Measure: Precisely measure 1 gram of Gentian Violet powder on a calibrated scale.
- Dissolve: In a clean glass beaker, add approximately half of your total distilled water volume. Slowly add the Gentian Violet powder while stirring gently until fully dissolved.
- Dilute: Pour the concentrated solution into a 1-liter volumetric flask (or other appropriate container). Add distilled water gradually while rinsing the beaker to ensure all the dye is transferred. Continue adding water until you reach the 1-liter mark.
- Label: Clearly label your container with the solution's name, concentration, date of preparation, and any relevant safety information.
Latent Print Processing with Gentian Violet
- Prepare Evidence: Ensure your item, primarily adhesive tapes, is dry. Gentian Violet primarily works with water-insoluble adhesives.
- Submerge: Gently submerge the adhesive side of the tape (or the item containing the suspected latent prints) in your Gentian Violet solution. Let it soak for 1-2 minutes.
- Rinse: Remove the item and rinse it thoroughly with distilled water to remove excess dye and stop the development process.
- Evaluate: Look for the emergence of purple-stained latent prints on the surface. If needed, repeat the soaking and rinsing for better development.
- Document: Photograph the developed latent prints immediately for preservation.
Storage Requirements
- Light-Sensitive: Store your Gentian Violet solution in an opaque bottle or in a dark location. It is sensitive to light and can degrade over time with prolonged exposure.
- Room Temperature: Keep your solution at a normal room temperature.
Shelf Life
A properly prepared and stored Gentian Violet solution can have a shelf life of one year or more. However, I always recommend checking for any signs of precipitation or discoloration before use.
Important Considerations:
- Carcinogenic: Gentian Violet is a suspected carcinogen. Always handle with extreme care, wearing proper personal protective equipment.
- Disposal: Follow your lab's hazardous waste disposal procedures.