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A New Method of Detecting Fingerprints on Paper
A New Method of Detecting Fingerprints on Paper R. L. GRANT, F. LYTH HUDSON, J. A. HOCKEY College of Science and Technology, Manchester, England As already announced briefly (Grant et al. 1963) a possible new method of detecting fingerprints on paper was discovered during the continuation of an investigation into the factors affecting the resistance of paper to attack by atmospheric pollution. At the time we were examining some autoradiographs of paper treated with sulphur dioxide, which is usually taken up preferentially near metal spots in paper (Hudson et al. 1961). Other spots in regular patterns were obtained and finger prints were found to be the cause of these. This note describes the experimental procedure in greater detail and gives some suggestions for future development of the method.
Experimental About 0.0015 ml. of radioactive sulpliur (sulphur-35) dioxide gas a t atmospheric temperature and pressure was measured from a simple vacuum system into an evacuated 150 ml. flask. The pressure inside the flask was raised to atmospheric by addition of air a t a controlled humidity of 66%. The paper was exposed to gas for 12 hours after which time the excess sulphur dioxide was removed by evacuation on the vacuum system. The paper samples were placed against X-ray film for one week (autoradiography) and on development showed preferential darkening in the regions where handling had occurred. Some examples of the prints obtained are shown in the diagrams ; the prints shown here are negatives, with reference to the X-ray film-the bright parts correspond to absorbed sulphur dioxide. The specific activity of the radioactive sulphur dioxide was about 1 millicurie per millimole. The quantity of gas to be added is not critical, but an excess is better than too little, although more than double the quantity stated above should not be used, since the excess combines with the paper and reduces the contrast between the images of the print and paper on the film. Radioactive formaldehyde vapour was also tried as a means of revealing the prints. The paper samples were exposed for 30 min. to the vapour from paraformaldehyde (carbon-14), of specific activity 86.3 microcuries per milligram a t room temperature and then left in contact with X-ray film for 15 hours. When developed the film showed a strong outline of the paper, but a weak and sketchy image of the print. Paraformaldehyde has been suggested as a useful reagent for this purpose (Sakaguchi, 1958). Results Of the four prints shown, Figure 1 represents one of the best obtained in the experiments. Figure 2 shows how, on a paper with heavy finger prints, the sweat deposits may diffuse from one ridge to the next, obscuring the outline of the ridge. The opposite extreme, and the more common case, occurs when handling is only light. An example is shown in Figure 3. The continuity of the ridges is poor and only the individual sweat ducts have been revealed. The outer parts of this print also show some metal spots. Figure 4 shows a print on a magazine paper of low quality. Sulphur dioxide has been picked up by the paper so that the contrast between the two regions is poor; this might be partially rectified by the use of contrast developer and printing paper. 85
Discussion
Disadvantages 1. Paper picks up sulphur dioxide to an extent which depends on its purity. Thus a good quality paper will pick up only sufficient gas during the time of the test to provide a clear contrast between the background and the print. For a paper made from a pulp with a high lignin content (such as a brown wrapping paper, or newsprint, and many packaging materials), the affinity for sulphur dioxide would be very similar for the two regions and clear prints would be very difficult to obtain. 2. A sample of paper with finger prints on it was left for 10 days in the laboratory before submitting it to the sulphur dioxide test described above. On development no prints were obtained. 3. Alkaline fillers, such as calcium carbonate, are added to certain papers and many coated art papers with a high gloss have alkaline fillers. On these papers the sulphur dioxide pick-up would be expected to be heavy and uniform and the detection of finger prints might be difficult. 4. Metallic impurities (iron and bronze) are present in all papers to different degrees ; they also pick up sulphur dioxide. An excessive number may therefore confuse the finger print. As metal spots contain iron or copper they can be detected after the remainder of the experiment is complete by treating the paper with weakly acid ferrocyanide solution. Advantages 1. The established methods used for the detection of finger prints on paper (Godsell, 1963) rely on a chemical means of producing a colour in the print which is then photographed. If the colour of the paper and print is similar the contrast is poor. The method described here is independent of the colour of the paper, and may also be more sensitive than colour reactions. 2. In cases where the print is too scanty for the ridges to be continuous, the individual sweat ducts (pores) remain visible, and can easily be used for classification purposes by established methods provided it is remembered that metal specks in the paper may produce identical spots. These may be differentiated by separate tests for metal on the original paper (Hudson, et al. 1961). Conclusion The few experiments we have done arose from a chance observation in an entirely different piece of research work. I t is quite possible that the use of sulphur dioxide could be developed to detect finger prints on paper but various matters, particularly the effect of time on the finger print, require investigation. I t is also equally possible that a more suitable volatile organic compound may be found. If this were done it would have the advantage of stability as the rate of decay of carbon-14 (half life 5,500 years) is negligible. I t is hoped that some further research will be carried out along these lines to develop a method for examining finger prints on paper and possibly on other porous materials too. Acknowledgment We would like to thank the Directors of Wiggins Teape and Company Limited for the grant of a research scholarship which made this work possible. References GODSELL, J., 1963, J Forensic Science Society, 3 (2) 79. F. LYTHand HOCKEY, J.A., 1963. Nature 200,1348. GRANT,R. L., HUDSON, HUDSON, F. LYTHand MILNER,W. D., 1961, Paper Technology, 2 (2), 155 SAKAGUCHI, M., et al. 1958, Second U.N. Conference on Peaceful Uses o f Atomic Energy, AIConf. 15/P., 1342. 86
Experimental About 0.0015 ml. of radioactive sulpliur (sulphur-35) dioxide gas a t atmospheric temperature and pressure was measured from a simple vacuum system into an evacuated 150 ml. flask. The pressure inside the flask was raised to atmospheric by addition of air a t a controlled humidity of 66%. The paper was exposed to gas for 12 hours after which time the excess sulphur dioxide was removed by evacuation on the vacuum system. The paper samples were placed against X-ray film for one week (autoradiography) and on development showed preferential darkening in the regions where handling had occurred. Some examples of the prints obtained are shown in the diagrams ; the prints shown here are negatives, with reference to the X-ray film-the bright parts correspond to absorbed sulphur dioxide. The specific activity of the radioactive sulphur dioxide was about 1 millicurie per millimole. The quantity of gas to be added is not critical, but an excess is better than too little, although more than double the quantity stated above should not be used, since the excess combines with the paper and reduces the contrast between the images of the print and paper on the film. Radioactive formaldehyde vapour was also tried as a means of revealing the prints. The paper samples were exposed for 30 min. to the vapour from paraformaldehyde (carbon-14), of specific activity 86.3 microcuries per milligram a t room temperature and then left in contact with X-ray film for 15 hours. When developed the film showed a strong outline of the paper, but a weak and sketchy image of the print. Paraformaldehyde has been suggested as a useful reagent for this purpose (Sakaguchi, 1958). Results Of the four prints shown, Figure 1 represents one of the best obtained in the experiments. Figure 2 shows how, on a paper with heavy finger prints, the sweat deposits may diffuse from one ridge to the next, obscuring the outline of the ridge. The opposite extreme, and the more common case, occurs when handling is only light. An example is shown in Figure 3. The continuity of the ridges is poor and only the individual sweat ducts have been revealed. The outer parts of this print also show some metal spots. Figure 4 shows a print on a magazine paper of low quality. Sulphur dioxide has been picked up by the paper so that the contrast between the two regions is poor; this might be partially rectified by the use of contrast developer and printing paper. 85
Discussion
Disadvantages 1. Paper picks up sulphur dioxide to an extent which depends on its purity. Thus a good quality paper will pick up only sufficient gas during the time of the test to provide a clear contrast between the background and the print. For a paper made from a pulp with a high lignin content (such as a brown wrapping paper, or newsprint, and many packaging materials), the affinity for sulphur dioxide would be very similar for the two regions and clear prints would be very difficult to obtain. 2. A sample of paper with finger prints on it was left for 10 days in the laboratory before submitting it to the sulphur dioxide test described above. On development no prints were obtained. 3. Alkaline fillers, such as calcium carbonate, are added to certain papers and many coated art papers with a high gloss have alkaline fillers. On these papers the sulphur dioxide pick-up would be expected to be heavy and uniform and the detection of finger prints might be difficult. 4. Metallic impurities (iron and bronze) are present in all papers to different degrees ; they also pick up sulphur dioxide. An excessive number may therefore confuse the finger print. As metal spots contain iron or copper they can be detected after the remainder of the experiment is complete by treating the paper with weakly acid ferrocyanide solution. Advantages 1. The established methods used for the detection of finger prints on paper (Godsell, 1963) rely on a chemical means of producing a colour in the print which is then photographed. If the colour of the paper and print is similar the contrast is poor. The method described here is independent of the colour of the paper, and may also be more sensitive than colour reactions. 2. In cases where the print is too scanty for the ridges to be continuous, the individual sweat ducts (pores) remain visible, and can easily be used for classification purposes by established methods provided it is remembered that metal specks in the paper may produce identical spots. These may be differentiated by separate tests for metal on the original paper (Hudson, et al. 1961). Conclusion The few experiments we have done arose from a chance observation in an entirely different piece of research work. I t is quite possible that the use of sulphur dioxide could be developed to detect finger prints on paper but various matters, particularly the effect of time on the finger print, require investigation. I t is also equally possible that a more suitable volatile organic compound may be found. If this were done it would have the advantage of stability as the rate of decay of carbon-14 (half life 5,500 years) is negligible. I t is hoped that some further research will be carried out along these lines to develop a method for examining finger prints on paper and possibly on other porous materials too. Acknowledgment We would like to thank the Directors of Wiggins Teape and Company Limited for the grant of a research scholarship which made this work possible. References GODSELL, J., 1963, J Forensic Science Society, 3 (2) 79. F. LYTHand HOCKEY, J.A., 1963. Nature 200,1348. GRANT,R. L., HUDSON, HUDSON, F. LYTHand MILNER,W. D., 1961, Paper Technology, 2 (2), 155 SAKAGUCHI, M., et al. 1958, Second U.N. Conference on Peaceful Uses o f Atomic Energy, AIConf. 15/P., 1342. 86