Some firearms, particularly revolvers, can actually deposit residues onto people at close proximity, which can sometimes obscure exactly who fired the weapon. Residues can also adhere to fired bullets and gradually lose themselves through the path of the bullet, and in certain cases can be found in targets up to 200 meters from the muzzle. A visual inspection of this close-range gunshot entrance hole shows visible soot and gunpowder. The first examination that the firearms examiner conducts is a visual and microscopic inspection of the wound or clothing submitted, to document any gunshot residues found around the bullet hole, as well as the shape and appearance of the hole. There are also two chemical processes that serve to enhance the visibility of residues not visible to the eye or microscope.
Orange color is a positive reaction to a presence of nitrite residues.
The first chemical test detects the presence of nitrite residues, which are a by-product of burned gunpowder. It is performed by first treating a piece of photographic paper with a chemical that makes it change color when it comes in contact with nitrite residue. The bullet hole in the garment or body is placed against the piece of photographic paper, and the paper is then subjected to the steam of a diluted acetic acid solution. The acetic acid vapors penetrate the object and react with any nitrite particles present to cause an orange stain to form on the photographic paper. A close-up of the work shirt seen in the first image, processed for lead residue.