A protective finishing coat is a substance or chemical composition applied to the surface of an object that provides a barrier of protection from external elements. Polishes use a highly refined abrasive (generally finer than 4,000 grit) that is suspended in a liquid carrier. The polish wears away the surface to create a smooth surface. The smoother the surface the higher the resulting gloss or perceived "shine". A protective finishing coat is applied after polishing to preserve the surface and help resist further oxidation or weathering. Effective finishing coatings penetrate the surface pores and use these pores to which the protective film anchors to.
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Protective finishing coat Wikipedia(Text) CC BY-SA