Stainless steel finishes are more than just a decorative touch for a finished project. In many cases, the finish is selected to serve a functional purpose, too. From adding to the lifespan of the steel to corrosion resistance and maintenance needs, here’s what you need to know about stainless steel finishes.
Form or Function
Choosing the right finish for a stainless steel project starts with what the purpose of the final product will be. In some cases, the appearance of the steel is a high priority. Additional fabrication processes will also dictate which finish is used. The structural needs of the final product can also help determine which finish is appropriate.
To ensure that designers and builders get the proper finish, the ATSM International Standards have defined and numbered the basic types of finishes. That way, a specific finish can be understood and selected across the industry. The three most common are matte, brushed, and mirror finishes. Let’s take a closer look at each of them.
The Number 2B Matte finish originates at the mill and is the most commonly used today. A matte finish is dull and is not considered an aesthetically pleasing finish. However, it’s the least expensive to use. It is also very acceptable when appearances are not important or when further metal fabrication or finishing will be completed.
To achieve a matte finish, surface oxidation is removed by a pickling process. Pickling is when stainless steel is treated with an acid solution to remove oxide scale and dissolve steel flecks embedded in the product. Then, a passivation layer is created before the steel sheet is cold rolled through specialized rolls to produce a smooth surface with very low reflectivity.
Typical applications for this type of mill finish include kitchenware such as bakeware and flatware, refrigeration and plumbing fixtures, and architectural flashing.
The Number 4 Brushed finish is most commonly found in architectural surfaces. It is often chosen for the lustrous finish and distinctive pattern of fine, parallel lines across the surface. The main advantages of a brushed finish are its resistance to corrosion and weathering, making it ideal for outdoor applications.
A brushed finish starts with a Number 2 matte finish that is then brushed and sanded in one direction. Much like working with wood, using progressively finer abrasives delivers the satin finish. Because the end result is not very reflective, this finish is also ideal when a great deal of reflectiveness is not desired.
Products with a brushed finish are often found on hospital surfaces, kitchen equipment and appliances, sinks, and architectural wall panels. The Gateway Arch in St. Louis is also faced with brushed stainless steel.
The highly reflective results of the Number 8 Mirror finish delivered an enhanced aesthetic appearance and consistency across the piece. The benefits of a mirror finish include ease of cleaning and the ability to mask the after-effects of welding and surface damage.
A mirror finish is achieved much the same way as a brushed finish, only with even finer abrasives and polishing compounds. Because it is highly reflective, a mirror finish should be avoided when glare or heat reflectivity will cause issues. For example, if a building’s exterior faces the sun, polished finishes can result in a dangerous glare created by the sun.
Consumer products are the most common to receive this highly reflective finish. It is also commonly used to create decorative trim, wall panels, signage, and reflectors. “The Bean” sculpture, located in Chicago’s Millenium Park, is also made from stainless steel plates with a Number 8 Mirror finish.
The Right Finish for the Job
Stainless steel is frequently chosen for its strength, resistance to corrosion, and, of course, its ability to be polished to a fine finish. From architectural projects to everyday household goods, stainless steel is an easy to clean, durable, and affordable choice for a wide variety of projects.