Analytical Examination of Clothing for Range Determination

Although in many cases soot and powder grains are readily seen on the clothing, thus indicating a close-range shot, on occasion examination with the naked eye and the dissection microscope is insufficient. The powder may have fallen and/or bounced off, or one is at the extreme range at which powder exiting a barrel will have sufficient velocity to embed itself in the material. In such situations and in instances where an exact determination of the range may be necessary, rather than just saying it is close-range, an analytical examination of the clothing is desirable.11 To make such determinations, Crime Laboratories use the Modified Griess test for nitrites and the Sodium Rhodizonate test for lead residues.12-13

The Modified Greiss Test

The Modified Greiss test is the evolutionary end product of the Walker test. This latter test was developed to detect nitrite compounds produced by the burning of smokeless powder (cellulose nitrate). The Walker test documents the presence of nitrites as well as showing the size, configuration and density of the pattern on clothing or other objects. A firearms examiner can then attempt to duplicate this pattern by firing the same weapon and type of ammunition, at know distances, at the same type of material. This procedure will give the examiner an approximation of the range at which the individual was shot. The test involves desensitizing glossy, photographic paper in a hypobath, washing and drying it, immersing it in a 5% solution of sulfanilic acid; drying it, dipping the paper in a 0.5% solution of alpha-naphthylamine in methyl alcohol, drying the paper, placing the clothing to be examined on the paper, placing a layer of cloth moistened with 20% acetic acid over the clothing to be examined, and pressing down on this cloth with a warm iron for 5 to 10 min. The paper is removed and washed in hot water and methyl alcohol. When nitrites are present, they will appear as orange-red spots on the paper which when retained constitutes a permanent record of the presence and distribution of the nitrite compounds.

Because alpha-naphthylamine was identified as a carcinogen, Watson introduced a variation on this test using Marshall's Reagent.15 The test then became known as the Griess Test. Subsequently, Marshall's Reagent was also found to be carcinogenic and was replaced by alpha-naphthol or naphthore-sorcinol. The former chemical will cause the nitrites to appear orange; the latter will make them appear yellow. This new test is the Modified Griess Test.12 Alpha-naphthol is the chemical currently used as the orange color is brighter. The Modified Griess Test, as was true of the other nitrite tests, will not interfere with subsequent lead tests using Sodium Rhodizonate, though the opposite is not so.

The Modified Griess test is specific for nitrites and thus, in theory, will not react with unburnt powder grains. Since these grains are usually coated with nitrite compound from burning of other powder grains, this is more theoretical than actual.

The Sodium Rhodizonate Test

The Sodium Rhodizonate test, long used as a spot test for lead and barium, constituted one portion of the Harrison and Gilroy test for the detection of gunshot residue on the hands.2 It is now used by firearms examiners for the detection of lead residue around an entrance.13 This lead is principally from the primer though some of it originates from the bullet and lead residue deposited in the barrel from previous discharges of the gun. In a modification proposed by Bashinski et al., the material to be tested is pre-treated with 10% acetic acid.16 This step improves the sensitivity of the test. The material is then sprayed with sodium rhodizonate followed by pH 2.8 tartaric acid buffer. Lead becomes visible as a bright pink reaction; barium has an orange color. Unlike the Modified Griess test for nitrites, the pattern of lead produced cannot be used to make exact range determinations. All that one can say is that the weapon was close enough to deposit lead on the article examined. Test firings can then determine the maximum range out to which the lead is deposited. If one has a hole and is not sure if it was due to a bullet, a sodium rhodizonate test can be done in order to see if there is lead on the margins of the defect. A positive test can be obtained even with full metal-jacketed bullets as these bullets may be coated with lead from the primer, the lead core or from deposits in the barrel. The Sodium Rhodizononate test is always performed after the Griess test as it may interfere with the latter test. The reverse is not true.

Negative Griess or Sodium Rhodizononate tests do not necessarily mean that the gun was not fired at close range as the gunshot residue could have been lost prior to the test.

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