Coloring of stainless steel is not a new concept. Any color can be obtained but only the surface color is changed – the base metal is inherently silver. Coatings and surface chemical treatments are the most common coloring methods. These methods can achieve grey and black colors but there are also other options, which will be addressed separately. The underlying finish affects both electrochemical and Physically Vapor Deposited (PVD) color, so both finishing steps must be carefully specified.
Alloy specification should be conservative. Superficial corrosion staining, which can often be removed from uncolored mechanical finishes without causing permanent damage, destroys PVD and electrochemical color and requires panel replacement. If the location has salt (coastal or deicing) or higher pollution exposure, the minimum specification should be Type 316/316L or alloys with equivalent or higher corrosion resistance. One illustration of this is a colored residential roof application described in the article Stainless Steel for Severe Coastal Environments.
Abrasion also removes surface color, so it is important to determine if wind-blown abrasives will be present (e.g. sand storms) and whether accidental or deliberate scratching is likely, before selecting a colored finish. An appropriate cleaning regime should be obtained from the finish supplier.
Some types of fabrication must be done before coloring. For example, welding melts the stainless steel and destroys color. Fabrication plans should be discussed with the finish supplier during design.
Any color is achievable. The color is translucent, so the substrate finish affects color, and appearance will vary with the lighting and angle at which the installation is observed. There are spectacular early projects where the original appearance of colored stainless steel has remained unchanged for decades – like Tokyo’s Reiyukai Shakaden Temple (completed 1975).