| Technology of fingerprint detection is progressing with the development of science,but it is still difficult to develop fingerprints on objects such as clothing and banknotes.Vacuum Metal Deposition?hereinafter referred to as VMD?has attracted attention due to its wide range of applications and high sensitivity.In this paper,the ability of latent fingerprints on the surface of the objects such as clothing,RMB?paper money?and substrates exposed to was investigated through experiments,which provided technical reference for fingerprint examination.The optimized condition was explored on aspects of the locations of fingerprint-carrying substrates,the amount of gold used to coat,the degree of vacuum and others,those factors affecting the developing effects.The study advised to place the substrates at about 15cm from the bottom of the cavity and meanwhile 4cm away from the door inside the IDenticoat500,and the initially-deposited gold wire not heavier than 3mg?about 2mm long?,and the vacuum degree held at 2×10-4mbar or even much lower,the fingerprints will be better developed.In the experiment about clothing,the influence of the type of fingerprint,legacy time and the type of object using VMD was investigated,finding that the effect of VMD on oil fingerprint is better than that of sweat fingerprint,and the object with smooth surface and weak permeability is better than the object with rough surface and strong permeability.With the extension of the remaining time,the quality of fingermarks may decline first,then recover and then decline.In the comparison experiment,unworn down jacket,the charge jacket,the cotton linen shirt,the cotton shirt were chosen as the substrates,and the effects of VMD,‘502'fuming and ninhydrin were compared.It was found that VMD was the best effect in loacting the fingerprints except cotton shirt.But as for the clothing that has been worn,for clothing more porous,the effect of ninhydrin is better than that of VMD.For clothing with low permeability,it is best to use‘502'glue to predispose before using VMD.In the experiments about RMB,1 yuan bank notes which were not in circulation,in circulation and wetted by water were used as object.The effects of VMD,indandione/ninhydrin were compared,finding that whether the renminbi were circulated,VMD behaved worse than indandione/ninhydrin.But for the wetted bank notes,VMD worked better.In the experiment about objects exposed to water,the influence of the type of fingerprint and immersion time using VMD was investigated,finding that the results were consistent with the investigation results of the influencing factors in the clothing experiment.In addition,it was still possible to develop the detail of the fingermarks that have been soaked for up to 50 days.Yellow tape?smooth surface?,tinfoil paper,plastic bag and glossy paper were chose as the non-porous substrates.VMD was compared with that of molybdenum disulphide?SPR?,and the results showed that the effect of VMD was better than that of SPR,except for the tinfoil.Copy paper,kraft paper,newspaper and thermal paper were chose as porous substrates,and VMD was compared with Oil Red O,finding that effect of VMD was not good,and VMD was not suitable for the development of latent fingerprints on the object soaked in water.The experiment showed that VMD could be used to develop latent fingerprints on the surface of the clothing with weak permeability and smooth surface,as well as the latent fingerprints on the surface of non-porous objects submerged in water.In the application of VMD technology,it should be plated with‘a few times',and it would be displayed again after the first plating,until the best effect was achieved. |
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