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NIJ, Firearm's Examiner Course, Module 12, retrieved April 25 2020 …

- - - - Visual and Microscopic Examination
        These examinations should be given priority because chemical testing can dislodge residues or alter appearance.
        Residue should first be observed by the unaided eye with a low power stereomicroscope. Infrared imaging can be used to visualize heavy soot on dark/bloody clothing. These exams should all be included in the lab notes.
        
        Physical Characteristics that may be visible during the preliminary exam:
        
        Hole in the material
        
        Visible ring around the perimeter of a hole (bullet wipe)
        
        Ripped or torn material in a stellate pattern
        -If visible, a distance determination could be made.
        
        Burned/Singed material
        
        Melted tips of artificial fibers
        
        Heavy vaporous lead residue (smoke) visible around bullet hole
        
        Burned or melted gunpowder adhered to surface.
        
        Types of gunpowder particles present
        
        Apparent particulate other than gunpowder
      - Chemical Testing:
        A sequence of chromophoric tests should be performed.
        Up to 3 tests may be performed sequence matters if more than one is performed.
        
        Griess Test for nitrite compounds
        
        Dithiooxamide Test for cuprous materials
        
        Sodium Rhodizonate Test for all forms of lead residues (Bashinski Transfer Technique)
        
        Sodium Rhodizonate Test can interfere with nitrite testing in the Griess test
        
        Modified Griess Test (Does NOT Use Marshalls Reagent)
        
        Focuses on the analysis of the size/density of patterns of nitrite residues on a victims clothing/objects and reproduction at known distances using suspects firearm in combination with the same type of ammunition.
        
        Does not yield positive result for NitrAte compounds (unburned powder)
        
        Chemistry:
        
        Nitrite residues exposed to acetic acid solution and heat to form nitrous acid.
        
        The nitrous acid combines with sulfanilic acid to form a diazonium compound of sulfanilic acid.
        
        The diazonium compound couples with the alpha-naphthol to form a bright orange azo dye.
        
        Nitrite Sensitive Emulsion-coated test paper: desensitized photographic paper that can be utilized as a medium for capturing azo dye. Preparation is the following: prepare solution of 7.7 grains of sulfanilic acid in 100 mL of distilled/DI water, prepare a solution of 4.3 grains of alpha-naphthol in 100 mL of methanol, combine equal volumes of the above solutions, pour the combined solutions into nonreactive photo processing tray that is briefly submerged and removed precut sheets of test paper into the tray, then set the sheets aside to dry on a clean surface or hung to dry, then store any unused solution in a sealed container labeled according to lab protocol, then store dried test paper in a dry place.
        
        Nitrite Test Swabs: prepared by preparing a solution of 9.3 grains of sodium nitrite in 100 mL of distilled/DI water, then soaking cotton tipped swabs in the nitrite solution, then setting the swabs aside to dry, and finally storing the swabs in a sealed container labeled according to lab protocol.
        
        Glacial Acetic Acid: prepared by combining 150 mL of glacial acetic acid with 850 mL of distilled/DI water then storing the solution in a sealed container labeled according to lab protocol.
        
        Cheesecloth: cut nitrite-free cheesecloth the size of the processed test paper
        
        Test Procedure:
        
        Confirm nitrite sensitivity of test paper
        
        Mark reference points of evidence on test paper
        
        Create layers of reaction items
        
        Heat reaction layers
        
        Examine and interpret the results
        
        Label and retain test paper
        Reverse Modified Griess Test
        
        Confirm nitrite sensitivity of test paper
        
        Mark reference points of evidence on test paper
        
        Apply acetic acid solution to test paper
        
        Create layers of reaction items
        
        Examine and interpret results
        
        Label and retain test paper.
        
        Dithiooxamide Test (Rubeanic Acid Test)
        Chromophoric test for the presence of copper-bearing material that comes from copper jacketed bullets. Copper is used in the following:
        
        Military and sporting jacketed bullets from gilding metal
        
        Rimfire bullets coated or plated with copper/brass
        
        Revolver bullets
        
        Nickle-plated bullets
        
        Chemistry:
        
        Material from perimeter of bullet hole exposed to ammonia solution
        
        Material then exposed to solution of dithiooxamide dissolved in ethanol.
        -A dark gray-green color: presence of copper-bearing material
        -A blue-pink color: presence of nickel.
        
        Dithiooxamide Solution
        Prepare a 0.2 % weight/volume solution of dithiooxamide in 100 % ethanol then store in a sealed container labeled accordingly.
        Ammonium Hydroxide Solution
        Prepare a 1:2 dilution on concentrated ammonium hydroxide using DI water under a chemical hood then store in a sealed contained labeled accordingly.
        
        Test Procedure
        
        Confirm performance of all prelim exams. (Modified Griess)
        
        Place test mark on item to be tested.
        
        Position the area to be tested (face up)
        
        Perform color test
        
        Examine and interpret results
        
        Dry test item
        
        Sodium Rhodizonate Test
        Chromophoric test for presence of lead in any form. This is performed after the Griess Test and the Dithooxamide Test. This test confirms the Modified Griess Test.
        Chemistry
        
        Questioned area is sprayed with saturated solution of sodium rhodizonate in DI water
        
        Buffer solution (pH 8.2) of sodium bitartrate and tartaric acid in DI water is sprayed. Pink reaction may indicate lead or another heavy metal.
        
        A dilute solution of hydrochloric acid is sprayed on the area. If pink area changes to blue/violet color then the presence of lead is confirmed.
        
        Saturated Rhodizonate Solution: add a sufficient amount of DI water to a small amount of sodium rhodizonate.
        2.8 pH Buffer Solution: Dissolve 29.3 grains of sodium bitartrate and 23.1 grains of tartaric acid per 100 mL of DI water. Heat and agitate. Store in sealed container.
        Hydrochloric Acid Solution: combine 5 mL on hydrochloric acid with 95 mL of DI water by carefully pouring acid into water. Store in sealed container.
        
        Test Procedure
        
        Confirm performance of all prelim exams (Modified Griess and Dithiooxamide test)
        
        Place a test mark on item
        
        Position area to be tested.
        
        Perform color test
        
        Bashinski Transfer Test
        
        Position area to be tested
        
        Place test mark on item
        
        Prepare filter paper
        
        Lift residues from item
        
        Perform color test.
        
        Label and keep filter paper
        
        Significance of Results
        Only residues that are present are a basis for reproduction and comparison. Residue can be absent due to careless handling, life-saving efforts of EMS, intervening object, masking of gunshot by blood/debris, short fired from distance beyond maximum distance for deposit.