It consists of metal brackets, plastic covers, catalytic cotton, catalytic cotton boxes and humidified water cups. With the metal bracket and the 502 cover on it, a 40 x 30 x 35cm confined space can be formed. Place the physical evidence on the bracket inside the cover and place the cup with hot water in the cover to humidify the environment inside the cover. After a period of humidification, put the box containing catalytic cotton into the cover and pour the appropriate amount of 502 glue into the box, which will be filled with 502 glue gas. After a while, the handprints on the physical evidence are visible.