The solution shall be neutralized using an excess of chemically pure copper oxide (1 g per litre of solution) and then the solution shall be left to rest for at least 24 h before decanting for use.5.3.3 Preparation of test pieceThe test piece shall consist of a piece of wire approximately 250 mm long, straightened by hand to a greater or lesser degree. This test piece shall be completely de-greased using benzene or any other suitable degreasing solvent. It is then rinsed in distilled water and wiped with a clean piece of cotton wool. After degreasing, the wire shall only be held at the end which is not to be dipped.In the case of a corroded wire or if other chemical substances remain present on the surface of the wire after degreasing (for example chromate or phosphates), the wire shall first be dipped in a 0.2 %sulphuric acid solution for 15 seconds and then rinsed.