Iodine vapor can be absorbed by the oil and fat material in the fingerprint left over, so that the fingerprint is dyed dark brown. Iodine is easy to sublimate at room temperature, the handprints shown by iodine-smoked method will gradually fade until they disappear, so the handprints smoked with iodine should be taken immediately. The handprints shown by iodine-smoked method disappear due to sublimation, so that iodine smoking has the advantage of not affecting other follow-up methods, the disadvantage is limited sensitivity.