Polishing is the process of creating a smooth and shiny surface by rubbing it or by applying a chemical treatment, leaving a clean surface with a significant
specular reflection (still limited by the
index of refraction
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
of the material according to the
Fresnel equations). In some materials (such as metals, glasses, black or transparent stones), polishing is also able to reduce
diffuse reflection to minimal values.
When an unpolished surface is magnified thousands of times, it usually looks like a succession of mountains and valleys. By repeated abrasion, those "mountains" are worn down until they are flat or just small "hills." The process of polishing with
abrasives starts with a coarse
grain size
Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which refer ...
and gradually proceeds to the finer ones to efficiently flatten the surface imperfections and to obtain optimal results.
Mechanical properties
The strength of polished products can be higher than their unpolished counterparts owing to the removal of
stress concentration
In solid mechanics, a stress concentration (also called a stress raiser or a stress riser) is a location in an object where the stress is significantly greater than the surrounding region. Stress concentrations occur when there are irregularitie ...
s present in the rough surface during the polishing process. These concentrations take the form of corners and other defects, which magnify the local stress beyond the inherent strength of the material.
Types
Metalworking
Other polishing processes include:
*
Burnishing
*
Mass finishing
**
Tumble finishing
**
Vibratory finishing
*
Sodablasting
Woodworking
*
French polishing
French polishing is a wood finishing technique that results in a very high gloss surface, with a deep colour and chatoyancy. French polishing consists of applying many thin coats of shellac dissolved in denatured alcohol using a rubbing pad lubri ...
*
Wood finishing
Other
*
Chemical-mechanical polishing, which is used in semiconductor fabrication
*
Fabrication and testing of optical components
*
Flame polishing, a type of polishing used on glass and thermoplastics
* Ultra-fine, abrasive paste polishing, polishing for soft or fragile work surfaces
*
Vapor polishing, a method of polishing plastics to optical clarity
References
External links
{{wiktionary
Decorative arts
Grinding and lapping
Industrial processes
Wood finishing techniques
Surface finishing