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Polishing is essentially an extension of the grinding stage on a much finer level. Its’ purpose is to remove all imperfections down to a microscopic level. During the preparation two stages of polishing were carried out. One using 1000 grit paper and one using 2000 grit paper, both of which attached to the rotating grinder via a magnetic coating on the underside of the paper. The respective RPMs of both disks were kept constant at 150PRM, however the time of a cycle was increased to 300s and the force applied to each sample was decreased to 15N per sample.

 

The major difference between grinding and polishing is the lubricant used. Whereas grinding requires a continuous flow of cold water to the grit paper, polishing uses a diamond paste which after an initial wetting is applied periodically, controlled by the interface of the polishing machine. This diamond paste is made up of particles of sizes on the macro meter scale.

 

Using the 1000 grit paper, a diamond paste with a particle size of 3μm was used. After a thorough cleaning and drying process, again using ethanol and a compressed air gun, the process was repeated using 2000 grit paper and a 1 μm particle sized diamond paste.

 

During the polishing process one of the specimens 350 proved particularly troublesome. Therefore an even finer grit paper of value 4000 grit had to be used in order to full remove the surface of all defects.