In any gunshot wound, powder residues may be left around the point of entrance of the bullet. Such residue may deposited either on the skin or clothing, or both. Usually these residues are invisible to the eye but can be located by infrared photography or microscopic examination in the laboratory. If the distance from which the shot was fired is an important factor, each piece of clothing with bullet holes should be preserved by insulating it between clean sheets of paper, in addition to wrapping it in such a way as to collect falling traces of powder residue. Bloodstain clothing must be air dried before packaging.