The same 304 or 316 sheet comes in very different finishes. Where are 2B, BA, No.4 satin and mirror finishes used, and on which do stains and marks show most?
The performance of a stainless sheet is not defined by the grade code (304, 316) alone; the surface finish is at least as important. The finish affects appearance, the visibility of fingerprints and stains, cleanability, and indirectly the tendency of dirt/chlorides to accumulate on the surface.
Surface finish codes are defined in the EN 10088-2 and ASTM A480 standards; the following are the four most commonly encountered types.
2B is a matte, smooth, low-reflectivity surface obtained after cold rolling, annealing, pickling and a light final pass (skin pass). It is the most common starting surface.
It is the default choice for parts that will be painted later, welded and ground, or put through another process.
The BA finish is produced by bright annealing in a controlled atmosphere; it gives a very smooth, reflective appearance, though not as deep as a mirror. Thanks to its low surface roughness it is easier to clean.
It is preferred in process equipment where hygiene is a priority and in decorative interior applications. Fingerprints are clearly visible.
No.4 is a fine, directionally lined surface brushed in one direction with an abrasive belt. It is the most common architectural finish, used for elevator cabins, countertops, handrails and facade cladding.
Because the directional texture camouflages everyday use marks and small scratches, it is practical in places that are touched heavily.
The mirror finish is obtained with progressive abrasives and felt polishing and has a mirror-like image. It is used in decorative panels, column cladding and signage.
Every speck of dust, fingerprint and scratch is clearly visible; it is the most laborious finish to protect and clean.
Quick decision guide: 2B for parts that will be processed or painted later; BA for processes needing easy cleaning and hygiene; No.4 satin on visible architectural surfaces to hide marks; mirror if a showcase effect is wanted and frequent cleaning is acceptable.
Both are cold rolled. BA is much smoother and more reflective thanks to bright annealing, while 2B is matte. BA is easier to clean.
The brushed No.4 (satin) finish is the type that hides marks best thanks to its directional texture. On mirror and BA finishes the marks show most clearly.
It does not change the corrosion class of the alloy. However, on smoother surfaces (BA, mirror) the passive layer stays more stable because less dirt and chloride accumulates; rough or heavily scratched surfaces are more open to local accumulation.
To a limited extent. Small scratches can be blended into the texture by hand or machine brushing in the same direction with a suitable grit. Field repair is much harder on mirror and BA finishes.
