Q39. How do you know that the results obtained from this test were not caused by a kitchen knife, or a knife fork and spoon?
A39. Firstly, most kitchen utensils are made from stainless steel or are nickel or chromium plated, none of which gives a positive result to this test. In addition, this whole test relies on the interpretation of the visualized marks on the hands. The examiner will, therefore, have to prove beyond reasonable doubt that the marks observed were those from a weapon and not something accidental such as a pry bar or a car jack.
Personally, I always carry a spray can of ferrozine with me when giving such evidence. A member of the court, jury or even the judge himself can then be asked to hold the object in question and then to have his or her hands sprayed. A highly effective technique. Q40. What other metals give a positive reaction to this test?
A40. The examiner should have knowledge of the interfering metals in this test and how to differentiate between copper and iron. He should also be aware, as any forensic chemist should, of the chemical processes involved, that is, bidentate ligand formation with ferrous ions.
Q41. How many times did you spray the suspect's hands? A41. A stock question to catch out the unwary. This is a qualitative test, not quantitative, and the number of times the hand is sprayed or the quantity of reagent applied to the hands has no bearing on the result.
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