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The Definitive Guide to Architectural and Commercial Metal Finishes

Editor’s Note: Mr. Darragh Harten, the article’s author, is Diamond Brite Metals new Business Development Associate. He can be reached at

Everyone in the metals supply chain understands the difficulties, and complete difference of opinion, surrounding the nomenclature for architectural and commercial metal finishes. What is a #4? What grits comprise a #6? 240-320 grit? What is the difference between a #8 Mirror Finish and a Super Mirror #8 Finish? This quagmire becomes even more daunting when RA and RMS finishes as well as vernacular finishes such as “hairline” and “vibration” are included in the lexicon. The difficulty in creating a definitive guide is the finishes imparted by architectural and commercial polishing escape objective categories. Since metals polishing is a mixture of art and science, a uniform nomenclature may not be achievable. The American Society for Testing and Materials (ASTM) and the American Society of Mechanical Engineers (ASME) have attempted to provide guideline definitions but those cursory parameters only touch on the most basic of metals finishes.

At Diamond Brite Metals, we pride ourselves on being the foremost resource for information regarding architectural and commercial polishing. To this point, we have defined the following architectural and commercial finishes:

#3 Finish: A polished finish obtained with abrasives approximately 100-120 grit.

#4 Finish: A general purpose finish obtained with abrasives approximately 120-180 grit. The 180 grit #4 is generally the finish requested for FDA grade finishes.

#6 Finish: A dull satin finish that is finer and smoother than a #4. Generally achieved with a 320 grit abrasive.

#7 Finish: A finish that has a high degree of reflectivity. Achieved through a 320-400 grit and then buffing. The underlying grit lines are not removed.

#8 Mirror: The most reflective finish obtained by polishing with successively finer abrasives (generally 600 grit) and very fine buffing with black and white compounds. The surface is essentially free of grit lines from preliminary grinding operations.

#8 Super Mirror: A finish achieved by the application of a non-directional orbital polisher over a #8 mirror.

Non-Directional Finish: A non-linear, uniform finish free of grit lines created by linear polishing followed by non-directional orbital polishing.

Longitudinal Finish: A non-circumferential finish produced on a pipe or tube.

RA Finish: A finish measured by the number of grit lines per micro-inch on a product's surface. Heightened regulations and specifications in different industries demand RA finishes because these finishes can be measured specifically with a profilometer.

We have seen the trend towards RA finishes in Original Equipment Manufacturers (OEM(s)) and end-use industries that are heavily regulated. The RA finish can be measured and certified thereby providing OEMs and other end-users, in industries such as pharma, biochem, oil & gas etc., with standardized metrics for commercial finishes.

Diamond Brite Metals can provide all architectural and commercial finishes. Our management and sales teams will work with you and your customer in design, processing and installation to ensure that your specifications are met. For an RFQ, please contact myself at or our sales team at



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