[1] A copper wire is cleaned and heated in a Bunsen burner flame to form a coating of copper(II) oxide.
It is then dipped in the sample to be tested and once again heated in a flame.
A positive test is indicated by a green flame caused by the formation of a copper halide.
One reason why it is not widely used is that it is possible to generate the highly toxic chloro-dioxins if the test material is a polychloroarene.
Addition of silver nitrate solution causes any halides to precipitate as the respective silver halide.