There are many different finishes in the polishing of metal. Finishing is useful because it usually improves the metal by reducing its chances of corrosion and it also enhances its aesthetic look and feel. In this article, we look into what a non-directional finish is in metal polishing and where it is used.
Before understanding the non-directional finish, let us understand where the importance of surface finishes arose. In the late 1970s, work at the British Steel’s Swinden Laboratories showed that dull, polished finishes on stainless steel exhibited a wide range of roughness on the surface. It was then revealed that the samples that had high surface roughness were damaged heavily by polishing operations. On the other hand, the samples with low surface roughness were relatively undamaged.
Dull polished finishes were used in many contexts during the mid-1980s. However, it became evident that the dull polished finishes were not good for resistance against corrosion, especially in coastal regions. Studies at the Swinden Laboratories showed clearly that surface roughness had a role to play in showing how corroded the steel would be. Whereas ‘coarse’ polished finishes had high levels of staining, ‘smooth’ polished finishes did not show as much staining. As a consequence, a new surface finish was introduced and now, continues to be used. Three common stainless steel finishes are: No. 2B - matte finish, No. 4 - brushed finish, and No. 8 - mirror finish.
A non-directional finish is also called a No. 8 finish or a mirror finish. It is a very smooth, highly reflective finish. As the name suggests, it is non-directional. It gives a very scratch free appearance to the stainless steel. By the standards set by the American Society for Testing and Materials, the No. 8 finish is the most reflective finish. In this finish, the grit lines are barely visible, even though they can be seen if scrutinized closely. Mirror finishes are created by polishing the stainless steel. Polishing improves the appearance and consistency of the steel. This makes it easier to clean the steel later. Furthermore, a mirror finish hides the after effects of welding and masks any damage to the surface.
To create the No. 8 mirror finish, the surface is mechanically treated with a series of progressively finer abrasives. Alternatively, another way to do it would be using a special rolling procedure which can simulate the feel of mechanical abrasion. For this particular stage, it is necessary to eliminate all deep scratches as any defects on the surface will be very visible on the final finished product. Finally, the last step will be buffing the surface for five to ten minutes in order to create a highly reflective, mirror-like finish.
Mirror finishes have a wide variety of uses. They are often used on those products that are required to be aesthetically pleasing. For example, architecture, artwork, and kitchen fittings would ideally use mirror finishes. However, aesthetic appeal is not the only benefit of a mirror finish. The mirror finish also increases the resistance of stainless steel to corrosion. Polishing gets rid of any scratches that could house corrosive particles. This makes mirror finishes invaluable in coastal regions, especially for architectural projects, because the stainless steel has to be exposed to salt air. Apart from this, the mirror finish has other applications such as: column covers, wall panels, and reflectors.
We at Diamond Brite are committed to excellence in all our services, including metal polishing. It is our mission to provide the highest quality finishing services for both architectural and commercial markets. We can provide our services for small and large commercial polishing projects. Our superior quality, excellent lead times, and unique capabilities make us the most reliable partner for service centers and fabricators for all kinds of polishing projects. Apart from the non-directional No. 8 mirror finish, we also specialize in the following: No. 4 finishes, Nos. 6 and 7 finishes, any custom finishes, and longitudinal finishes.