The purpose of silverware burnishing is to both physically and chemically clean and smooth the fine surface ‘grains’ of the metal. This is accomplished through the use of a barrel tumbler and the appropriate tumbling media and compound.
Stainless steel burnishing balls (media) are used to force the metal to ‘flow’ and fill the scratches on the surface. As the entire load is rotated in the barrel, the media lifts up the back side of the the barrel and cascades towards the front. As the parts are carried with the media in the sliding area, the weight of the burnishing balls impact with the surface of the silverware. This contact forces the metal to fill the low spots and even out the high spots.
In combination with the physical polishing, the water and burnishing compound help to remove the tarnish (silver sulfide) and keep the process lubricated. Using the proper compound (and changing the solution regularly) will limit damage to the silverware in process and keep re-deposition to a minimum.
The combination of chemical cleaning and microscopic, physical manipulation leads to a bright and polished surface finish.