Stainless steel with a finished surface provides a modern, decorative look to all types of built structures. Current technology allows for an extensive amount of finish types and techniques. The sections below will describe the different types of stainless steel finishes. Be aware that finishes are different from grades, which are described in our article about Stainless Steel Grades.
Stainless Steel Finish Designations
Prepared stainless steel surfaces are assigned number designations ranging from 03 to 10 based on the coarseness of the surface, with 03 representing the coarsest finish and 10 representing the smoothest.
03: This finish is known as a rough-ground finish. Grinding is accomplished using a rough abrasive, and metal with this type of finish is typically in the state of being prepared for additional work. A 03 finish is not normally used in any type of final product.
04: This is commonly called an architectural or brushed finish. The grit on the finishing belt is used to create polishing lines of uniform thickness. Typically the lines are created in a parallel pattern, but can be modified to provide alternative designs as described in Special Finishes below. Brushed finishes are typically less resistant to corrosion than smooth finishes due to a higher likelihood of water or other fluids becoming entrapped within the grooves and creating an environment more susceptible to oxidation.
05: A 05 is known as a sanitary finish. 05 stainless steel is commonly used for kitchen appliances and medical equipment. This finish is designed to remove any type of pitting on the surface of the steel that would create a reservoir for bacterial growth.
06: This is called a fine satin finish. The overall concept is similar to an architectural finish, but since the polishing grit is finer the lines remaining after polishing are less defined and shallower, which creates less reflective faces on the steel.
07: A 07 finish is polished and buffed to a point that provides a shine but not necessarily a flawless finish. Steels that will be receiving a chrome plating are often polished to a number seven.
08: The mirror finish of a 08 is accomplished using a very fine grit and is polished to a point where all noticeable surface defects are removed. This finish is not always achievable if excessive pitting is present.
09: A 09 or bead-blast finish is created by applying a high-velocity air stream to the steel that contains abrasive material such as sand or glass beads. Very small pits are created in the metal surface that provides a consistent matte finish. Glass beads typically create a finely textured surface with a silver look, while very small sand particles will create a coarse surface with a medium to dark gray color.
10: Electropolished surfaces are classified as a 10 finish. In electropolishing, an electrically stimulated chemical reaction is used to remove particles from the metal surface (basically the opposite of electroplating).
The image below shows a 04 brushed finish with a horizontal grain pattern. Architects should make sure to specify the grain direction for any brushed surfaces in the contract documents.
Special Stainless Steel Finishes
In addition to the various types of coarse to smooth finishes that can be applied to stainless steel, there are several different types of finishes that can be created to give the steel a particular look and feel.
Swirls and Circles
Swirls and circles can be applied to steel using an abrasive pad to scratch the pattern into the surface. Concentric, ordered layouts can be created, or random swirls (often referred to as Random Orbital) may be created over the entirety of the steel surface. The creation of ordered layouts of inscribed circles into metal is sometimes known as engine turning.
Patterns can be stamped into thin sheets of stainless steel to provide a virtually infinite variety of geometric finishes, many of which mimic patterns found in other types of materials. Some examples of patterns are natural looking sandstone and brick, geometric-based patterns such as raised circles and squares, and also patterns which are custom-made for particular applications such as those that include a company logo.
A distressed finish consists of random scratches applied to the steel surface through the use of a wire wheel. This pattern is often used in locations with high pedestrian traffic, as minor scratches resulting from contact with the metal would be hidden inside the pattern. A distressed finish pattern that is composed of very small thin lines is commonly known as Angel hair.
Steel can be etched using an acid to strip away the surface layer and create a rough, matte, silver-gray finish. This technique allows the creation of an extremely varied amount of designs, particularly through use of temporary protective coatings that allow for modification of select portions of the steel. Etching is commonly used to inscribe text, company logos or linework into the surface of the metal.
Pickling is a type of treatment used to remove a thin layer from the surface of stainless steel. Oxide or scaling can develop on stainless steel from exposure to high temperatures, such as those experienced during heat treatment or welding. The pickling process involves submersion of the steel in acid or application of a stiff acid paste (known as pickling paste) to break down and remove the hardened scale and a layer of the steel surface. Once the pickling process is complete, steel is normally passivated, which regenerates the oxide film on the steel surface and restores its ability to resist corrosion.
Electroplating is a technique used to apply a very thin coat of metal to the surface of an electrically-conductive material. Since metal is an excellent conductor of electricity, this method provides a relatively easy means of applying surface finishes. The process involves immersion of the object to be coated and a solid piece of the coating material in a solution. The solution will also contain molecules of the coating material. Using a direct-current power source, the object to be coated is connected to the negative terminal, which results in the coating metal adhering to the surface of the object.