For examination under microscope metal surface should be free from scratches. It should have mirror finish. This is achieved by polishing the surface in stages. This consists of polishing by belt grinder followed by manual polishing using different grades (0, 00, 000)of emery papers from coarse to fine. For hard metals like steel dry polishing is good enough. For soft metals like aluminum you need wet emery paper. Take care to wash the sample after each stage. If the sample is too small to grip by hand it may be mounted (fixed) in Bakelite or sample holder. After emery paper finish move over to wet polishing on cloth mounted on rotating disc. The cloth is kept soaked in water having fine suspension of polishing powder. After this if you look under microscope you would see a shining flat surface. Inclusions (or graphite in cast iron) if present may be visible. You need to etch the sample to see other fine details like grain structure. Use nital (2% HNO3 in alcohol)to etch steel.
Prof. R.N. Ghosh Date: