The 502 glue-smoking method is the preferred method for the appearance of potential fingerprints of sweat on non-permeable objects. After the volatile monomer of cyanate acrylates in 502 glue, the gas molecules converge on the handprint line to form a white substance. If the contrast of fingerprint lines after 502 glue treatment is weak, the contrast can be increased by dye dyeing, ultraviolet photography or directional reflection photography.