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Homemade Solution for (The following article is reprinted from the Jan. `98 issue of Gopher Identification, published by the Minnesota Division of the I.A.I.) by JANET NELSON Members of the U.S. Secret Service Forensic Services Division Identification and Research Branch at the 1997 IAI Conference at Danvers presented a new method of developing fingerprints on the adhesive side of tape. Participants in the workshop then tested the new “homemade recipe” against “Sticky--side Powder® and SPR on various tape surfaces. Fingerprint Specialist Carey Chapman explained that since Sticky--side Powder and Liquid Powder® are trademark names, they had to find another name for their technique. Hence, they christened it “Powder Suspension Solution.” Yawn. But...their lack of imagination in naming this nifty little process is overshadowed by how well it works and by how ridiculously cheap and easy it is to made and use. Members of the class actually chuckled with amusement and asked; “That's it?”, when told of the ingredients...equal parts of black fingerprint powder, clear liquid dish soap, and distilled water. No fooling, that's the entire recipe! The dish soap performs the same purpose in this solution as Photoflo® does in SPR. Other accessories required for the process are a supply of camel hair brushes (either thick art brushes or the smaller flat fingerprint brushes) and some plastic disposable bowls (the ones made by Solo® work well). If there were still any doubters of this process after Carey finished the classroom portion of the workshop, they were converted to believers when we tested and compared the technique against commercial products. Latent prints on gray duct tape, strapping tape, tan packaging tape, and black (electrical) plastic tape were processed side by side with the “Powder Suspension Solution,” Sticky--side Powder, and Small Particle Reagent (SPR). The black powder solution produced latent prints that were noticeably darker than the latents processed with Sticky--side Powder and SPR. It appears that the latter two are more bichromatic and thus produce lighter results. A similar homemade solution using white powder in place of the black powder was tested on the black tape and was found to work equally as well as its counterpart. We were also provided with some samples of tapes that had been processed with Cyanoacrylate (CNA) a.k.a. Superglue to develop latents on the smooth side of the tape. Gentian Violet was available to stain the latent images after they were developed. I did not have the opportunity to test these methods. A. Preparation of the powder suspension solution: Use equal parts of distilled water, liquid detergent (i.e., Photoflo, clear Ivory®/Palmolive® dish soap, or lab glassware soap) and black/white latent print powder to make the solution. The following measurements provide a starting point for your mixture. 1. Measure 1 teaspoon of distilled water into a dish. 2. Measure 1 teaspoon of liquid dish soap into the dish with the water. 3. Measure 1 level teaspoon of fingerprint powder into the dish with the water and soap and stir the solution with a camel hair brush until it is well mixed. B. Application of the powder suspension solution: 1. Put distilled water into a second dish or pan. 2. With the camel hair brush, `paint' the powder suspension solution onto the adhesive surface of the tape. 3. Rinse the `painted' tape in the dish of distilled water. 4. Examine the developed detail. If desired, an additional application of the powder suspension solution can be reapplied to the tape, following steps #2 and #3. 5. If using a two step method for processing black or dark color surfaces, prepare two solutions by following steps #1 through #3 in section A. Use black latent print powder for preparing one solution and white latent print powder for preparing the other solution. Use separate camel hair brushes for mixing and applying the solutions. Apply the black powder solution (following steps #1 through #3 in section B.), then apply the white powder solution (following steps #1 through #4 in section B.). C. Validation Testing of the Powder Suspension Solution: 1. Obtain a sample piece of tape. 2. Place a control print on the adhesive side of the sample. 3. Apply the newly prepared powder solution onto the adhesive side of the tape. 4. Rinse the painted the tape sample in a dish or pan of water. 5. If the solution was properly prepared, the control print on the sample should develop and appear black (if black powder was used in the solution) or white in color (if white powder was used in the solution). 6. If the validation test result is negative, repeat steps #1 through #4 with a second control sample. (Use a different print donor). 7. If the result of the second test is negative, the solution should not be used for processing. Properly dispose of the solution. 8. If any additional problems are encountered, seek the assistance of an examiner or specialist familiar with the solution and technique. Miscellaneous notes and observations: <The solution works better if it is mixed in the order given. <It will look bubbly. <If the solution is too thick, add more water but not more soap. <Use cloth gloves (like photofinishers wear) to pull stuck tape apart. <Experiment with moistening the tape prior to applying the solution to increase the contrast of the print and the background. <Use superglue first to process the prints on the smooth side and the suspension solution next. <Use Gentian Violet before powder suspension. <Paper tapes such as masking tape and paper packing tape and labels yield better results with Ninhydrin than with the powder suspension solution. <The colder the water, the better the solution works. <Use only clear liquid soap. The colored soaps or those containing lotions don't work. <Use clear nail polish to fix the prints on the tape. <The solution can be applied by dipping or by painting--—it depends entirely on personal preference. <Rinse off the excess solution by submersing and agitating the tape in a shallow pan of cool water. <Gray powder does not work well. <Some fluorescent (basic yellow) powders will also work in place of black. <Good use for old lumpy powders (just make sure the lumps get dissolved in the liquid).
Questions/comments regarding this technique may be referred to:
This article was printed in “THE PRINT” |