Study On The Optimal Condition For Fingermark Development By Physical Developer

Physical developer is an important method for developing latent fingerprints on wet porous surfaces,and it is a well-established fingermark development method abroad.However,this method has not been applied in China because it has a plethora of issues associated with its use,principally based around the preparation and relative instability of the working solution.Therefore,the optimization of the formula and the construction of a complete operation procedure of physical developer can improve the developing effect of latent fingerprints on wet porous surfaces effectively,which could improve the developing effectiveness and is of great significance in casework.In view of the above problems,the following research is carried out in this paper:The optimal development formula and storage conditions are determined.Using the split depletion method,to assess developed fingermarks with the comparative and absolute scale.It is concluded that the optimal developing formula of the detergent surfactant solution is the 2.8 g/L tween 20 solution.The optimal storage temperature of surfactant solution is 5℃,and the ageing time has no effect on the developing effect.Use the redox solution right after it is ready.The optimum ageing time for working solution is 7 days.The effect of temperature on the developing of physical developer has been studied.The results show that the best developing temperature is 30℃.By studying the fingerprints and particle change within 30 seconds to 15 minutes,it is concluded that the silver particle is the maximum at 30℃,the medium at 20℃,the minimum at 40℃.The higher temperature is,the silver particle nucleation time come earlier,appeared to achieve the best effect of the earlier.When the temperature is 40℃,silver particles began to accumulate,leading to ridge "adhesion",which made the developing effect reduced.This paper constructs and tests the complete operation procedure of developing fingerprint of physical developer.The effects of physical developer on different paper are studied,and the result shows that the developing effect on white paper,copy paper and manuscript paper is of good value,while on newspaper and kraft paper is of little value.The developing effect of fingerprints of 150 volunteers on the copy paper is studied,and the result shows that the optimized physical developer had a better developing effect on dry(the identifying rate is 58.67%)and wet(the identifying rate is 43.33%)surfaces,and it could be applied to casework better.