An etchant was used to electively etch the grain boundaries. Mention whether these grain boundaries would appear brighter or darker after etching when observed through optical microscope and explain the reason for such appearance.

Explanation:

a. Polishing or fining of a metal sample is done to get a mirror finish of the metal in order to get a clearer or good view of the materials composing of the metal under the microscope view. Polishing will not give the whole structural view. Etching is done to give the microstructure of metal by applying selective chemical attack. Polishing are also removed through the process of etching, thin grinding layer which are brought by polishing.

2. Grain boundaries are been harmed by chemicals more than the entire grain are been affected. In an optical microscope view, scattering of light is base on how the surface is etched. As the grain boundaries becomes more etched, more light is been reflected therefore given a dark appearance of the grain boundaries in the microscope view.