|
|
|
Procedure to Develop (The following article is reprinted from the Oct./Dec. `97 newsletter published by the Pacific Northwest Division of the I.A.I., where it had been reprinted from the Jul/Aug/Sept. 1996 issue of Identification Canada.)
By CORPORAL PIERRE MCMAHON Thermal paper used in several fax machines presents some difficulties when looking for latent prints. One side of this paper is coated with a reactive substance which turns blue or black between 90oC and 110oC. Once dipped into ninhydrin or DFO, solvents used in these solutions dissolve the reactive substance and blacken the paper, thus considerably reducing the possibility of developing useful prints and altering the original document appearance. A procedure called “nin--dry” developed by Marty Ludas of the Raleigh North Carolina Police Department overcomes these difficulties and provides very satisfactory results. Procedure: 1. Dissolve 30 to 50 grams of ninhydrin in 1,500ml of acetone. 2. Cut pieces of blotter to the size of the documents to be examined and soak them into the solution. 3. Let them dry for a few minutes under a ventilation hood. 4. Place each document between two blotters and seal them in a plastic bag for a period of three (3) to seven (7) days. Ludas used an iron to heat the blotters after placing them in a damp towel in order to speed up development. This last step is not recommended for thermal paper. This procedure seems to require a lot of time and patience. To experiment with this procedure, prints were placed on both faces of thermal paper samples by individuals chosen at random. After a week, samples were placed between two pieces of blotter pre--soaked in a ninhydrin solution. After a period of three (3) to seven (7) days, useful prints appeared on both faces of samples without paper appearance being changed. This procedure may also be used with DFO samples (see Journal of Forensic Identification 45(2) 1995). However, it is not recommended for thermal paper as blotters must be heated at 110oC in a mounting press and thermal paper begins to blacken at 60oC when placed in an incubator. The main advantage of the “nin--dry” procedure when dealing with thermal paper is the preservation of the document appearance and the creation of a good contrast allowing for the photography of prints.
This procedure is also applicable to other types of documents, particularly
when paper brittleness and ink smearing are a concern. Bibliography: 1. Ludas, Marty, Raleigh Police Department, Raleigh, North Carolina. 2. Bratton, M.R., Michigan State Police, Journal of Forensic Identification, 45(2) 1995. 3. Le Petit Larousse 1992, page 1006.
This article was reprinted in “THE PRINT” |