Visualization Of Latent Fingermarks On Challenging Substrates Using Metal Deposition

Metal deposition is a versatile fingermarks detection technique which can be divided into multi-metal deposition（MMD）and single metal deposition（SMD）according to the type of metal used.In order to explore the potential of metal deposition on challenging substrates and to explore the unique advantages of metal deposition,this paper used a variety of different metal deposition formulations,and selected several common fabrics and leathers for the following experiments:By comparing the effect of different combinations of formulations,different p H values and different Tween-20 concentration,this paper determined the most suitable formulations of developing fingermarks from different substrates.The results showed that for the fabric and cow leather MMD I demonstrated the best effect;for PU and PVC leatheratte the most suitable formula was MMD III;the optimal p H value varied widely from different substrates;while the Tween-20 concentration influenced slightly on the final quality of developed fingermarks.In the experiment of fingermarks visualization on fabric,the influence of different types of fingermarks,donor quality levels and substrates on the effect of MMD was investigated,and the performance of MMD and VMD on six different fabrics with different aging period was compared,as well as the effect brought by water immersion.The results showed that MMD performed well on all kinds of fingermarks and donors;on nylon,polyester and satin MMD developed most of the fingermarks with high quality.MMD was overwhelmingly superior to VMD on fabric surfaces,and for fingermarks left on nylon,polyester and satin surfaces aged over28 days the identifiable rate still reached above 30%.Water immersion did have some observable influence on the quality of detected marks as part of the MMD reactants within fingermarks lost during immersion,but the result from nylon taffeta and satin ribbon is still satisfying with the percentage of marks scored 3 and 4 reached 30%.In the experiment of fingermarks visualization on leather,same influencing factors as the previous chapter on the effect of MMD was investigate,and the results are as follows: for different fingermarks types,different donors and different leather substrates MMD generally showed good performance.The mean score of fingermarks on leather surfaces developed by MMD remained around 2 when aged 14 days,which was superior than the mean score of fresh fingermarks treated by VMD,even after 28 days of deposition,the identifiable rate of fingermarks revealed by MMD was still higher than 20%.Water immersion influenced the quality of fingermarks developed by MMD on all three leather surfaces.However,even after 84 hours of immersion,the mean score of fingermarks still remained around 1.6.