Finish terminology for standard mechanically abraded and buffed surfaces varies around the world as can the typical appearance, gloss (reflectivity) and surface roughness of a particular finish. For large projects where finish matching is critical, it is important to agree on a visual standard as well as acceptable surface roughness and gloss (reflectivity) tolerance ranges and other quantifiable characteristics before placing the order.

Surface roughness can have a tremendous influence on corrosion performance and dirt retention. Table 2 provides the results of a survey of North American and European surface finish providers and the roughness ranges associated with some of these finishes. IMOA has a Finish Specification webpage, which provides brochure and website links to more information on finishes, quantifying key characteristics, and corrosion performance.

Standard Polished or Linished Finishes

These “standard” finishes are the mechanically abraded and buffed finishes, which are defined by international standard specifications. The terms “polished” and “linished” are both used to describe these finishes in different parts of the world. Standards describe the production processes used to obtain them and the general appearance but not quantifiable characteristics. Images of these finishes can be found on SSINA’s website.  ASTM does not distinguish between the fine wet and rougher dry versions of the No. 4 polish. JIS and Euronorm standards use No. 240 and 2K, respectively, to identify this finer polish.

Table 1: International standard cross reference

Non-Standard Mechanical Finishes

These finishes are not described in international standard specifications. The generic terms for them have been used below. Variations on these finishes are also sold under trade names and are often aesthetically unique.

Highly Buffed Mirror Polishes

The ASTM A 480 No. 8 or EN 2P polishes have been abrasively polished and then buffed but remnants of the polishing lines are still visible under close examination.  True mirror polishes are sold as Super No. 8, 9 and 10 (or some higher numbers) and are mechanically polished and then buffed. They are a higher quality finish than a buffed Bright Annealed (BA) mill finish. Determine what polishing media was used. Some low cost suppliers use iron oxide, which can contaminate the surface and cause corrosion. Applications range from decorative panels to bathroom mirrors.

Table 2: Typical sheet and strip finish roughness ranges from North American and European stainless steel suppliers.

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5. Deicing Salt: Stainless Steel Selection to Avoid Corrosion
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7. Advanced Stainless Steel Specification and Problem Avoidance
8. Specification of Stainless Steel Finishes and Grades For Corrosive Applications

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IMOA (International Molybdenum Association) is a non-profit industry association, which provides technical information to assist with successful specification of molybdenum-containing materials. Molybdenum is an element. When it is added to stainless steel, molybdenum increases its resistance to corrosion caused by deicing salts, coastal atmosphere and pollution.

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