Technical Note

Rhodamine 6G

Introduction

Rhodamine 6G is an excellent laser or Forensic Light Source dye. It can be dissolved in water or solvents to be used as a liquid dye in solution staining, or it can be introduced into magnetic powder to form a fluorescent magnetic powder. It is the dye of choice of many latent print examiners.

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. With Rhodamine 6G, it is recommended that rubber gloves and safety glasses be worn. When combined with any of the solvents listed below, the solution should be mixed and used in a fume hood. When examining the evidence with a light source, wear protective goggles. Be familiar with the light source and know which goggles to wear under all circumstances.

Mixing Instructions

While there is more than one formulation for mixing Rhodamine 6G, the simplest formula uses about 0.1 gram per 2-3 liters of carrier. The carrier can be either distilled water or a solvent such as methanol. With larger, powerful lasers, a more dilute solution may be more effective or with a small, portable unit, a less dilute solution could be better. There is room for experimentation for each type of laser or Forensic Light Source used. Because each piece of evidence is different, a test should be done using the aqueous (water) solution and the methanol solution. On some types of materials, the methanol solution will absorb into the item and the whole surface will then fluoresce. On other items, the aqueous solution will absorb, causing unacceptable results.

Glue Fuming

Before using Rhodamine 6G, it is necessary to glue-fume the piece of evidence. It is recommended to underfume rather than overfume. If heavy white residue is present on the background surface or heavy white latent prints are developed, the Rhodamine 6G solution may stain the entire surface and the latent prints will appear as bright glowing globs with no ridge detail when illuminated with a light source. The use of fast-acting, chemical catalysts or accelerator pads is not recommended, as the process can develop heavy, white residue.

Place a few drops of liquid glue or a Hard Evidence™ Pouch in a closed container, such as a fish tank, with the evidence and a cup of warm water. Allow the evidence to remain about ten minutes before checking. To check the progress of the fuming without opening the lid of the fish tank, place a black latent print backing card in the tank with test prints on it. When these test prints are just becoming visible, remove the evidence from the tank to stop the process.

Fuming under vacuum with a Coleman Vacu-Print™ will help to eliminate the problems associated with overfuming. Vacuum technology for glue fuming is relatively new. This method will develop latent prints without excessive residue coating the surface of the evidence, and it will be easier to handle the evidence.

Because there is no residue buildup on the evidence, dye-staining for fluorescent examination is more effective. When there is excessive buildup of the glue residue, the dye stains all of it, causing the entire surface to fluoresce, perhaps obscuring ridge detail.

With a vacuum process, items of evidence, such as garbage bags do not have to be opened up. The fumes will coat all of the surfaces. Also, items such as soda cans, screwdrivers and handguns can be placed inside the chamber with the items touching each other. It is not necessary to leave space between each item. For additional information on the Coleman Vacu-Print™ vacuum fuming chamber and glue fuming processes, see their respective technical notes in this section.

Examination

Dim the room lights and shine the light from the Forensic Light Source or laser over the surface of the object. Photograph the visualized latent prints. For those using a variable wavelength Forensic Light Source, examine the evidence using 450 to 480 nm wavelength of light and view with orange goggles.

Photography

To photograph the fluorescent-developed latent prints, duplicate the arrangement by which the best contrast was viewed with the eye. Include a fluorescent scale in the photograph next to the evidence. Use the wavelength, the color of viewing goggles and the angle of the light source to obtain the best photograph. Using a fine-grain black and white film with a medium ƒ-stop (ƒ/8 or ƒ/11) will give a photograph showing highly defined ridge details. The ridges of the latent print will be white and the background will be dark in the resulting photograph.

To reverse the color of fluorescent-developed latent prints, take the photographs using slide film, such as Polaroid PolaPan, to see the results in just a few minutes. Print the slide film on regular black and white photo paper to see the ridges dark and the background light. For additional information on photography of fluorescent latent prints, see our fluorescent photography technical note.

Additional Reading

Advances in Fingerprint Technology edited by Dr. Henry Lee and Dr. R. E. Gaensslen
Manual of Fingerprint Development Techniques by the British Home Office, second edition
Fingerprint Detection by Fluorescence Examination by the British Home Office
An Introduction to Lasers, Forensic Lights and Fluorescent Fingerprint Detection Techniques by Dr. E. Roland Menzel

Ordering Information

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