| Whenever a firearm is discharged, the primer and the | | | | patterns are easily identifiable as smudges or smears, |
| powder detonate inside the cartridge, violently | | | | but on dark, multicolored, or blood-soaked clothing, |
| pushing the bullet down the barrel. Most if not all of | | | | the patterns are not too evident. |
| the explosive gases and particles created by the | | | | GSR residues can be identified by infrared |
| explosion follow in the bullet's wake. Some of these | | | | photography under substandard circumstances. The |
| particles pass through an opening in the firearm. This | | | | Griess test may also identify the pattern. This test |
| is very true for revolvers, which has a tendency to | | | | involves the use of filter paper soaked in vinegar that |
| leak more gases than semiautomatic firearms. | | | | when pressed over the area in question and then |
| The combination of chemicals and particles of these | | | | immersed in a reagent that interacts with the |
| gases are collectively known as gunshot residue | | | | nitrogen containing compounds found in GSR yields a |
| (GSR). Gunshot residue sticks to the firearm user's | | | | GSR pattern. Photographic paper can also be used in |
| hand, arm, clothing, hair, and face. They also stick to | | | | place of filter paper to reveal evidence of a GSR |
| nearby walls, curtains, or future and on the victim's | | | | pattern. |
| clothing and skin in close-up shootings. | | | | The next time you watch your favorite CSI TV |
| Weather such as wind and rain can alter the pattern | | | | show, you will have a better understanding of what |
| of or reduce the spread of the cloud of GSR. In | | | | the procedures are when criminal scientists run tests |
| effect, the forensic firearms expert may find GSR in | | | | to disclose the presence of a GSR pattern made of |
| places he would least expect. On white clothing, GSR | | | | gases and particles. |