Alow me to quote from the National Metal Finishing Company:
NICKEL:
Bright Nickel Plating:
Bright nickel plating baths use combinations of organic chemical additives to achieve bright nickel deposits. Bright nickel is used under decorative chrome and other final finishes to cover small defects such as polishing lines and to provide luster. Nickel can also be used as a final finish for certain applications, such as in the plumbing, lighting, and furniture industries.
Matte (Pearl) Nickel Plating:
Matte nickel plating is a uniform finish that is semi-lustrous with low reflectivity. It is also referred to as pearl or velour nickel; it does not have the lines or grainy appearance found in traditional satin nickel finishes. Matte nickel is usually coated with chrome, black nickel or another final finish. It is used in the plumbing, optical, lighting, and automotive industries. Satin (Brushed) Nickel Plating:
Satin nickel plating is a nickel finish that is semi-lustrous with some reflectivity. It is also referred to as brushed nickel; it does have lines or a grainy appearance that is applied by mechanically polishing the surface before or after the nickel plating. It is used in the plumbing, lighting, and furniture industries.
Bright Black Nickel Plating:
Black nickel is plated over bright nickel to give a lustrous black appearance. It is brighter than black chrome and covers recessed areas better. Since the black nickel coating is quite thin, corrosion resistance is somewhat limited. To improve corrosion protection, the black nickel or bright nickel may be applied over electroless nickel, but the black color may not hold up in severe environments. It is used for optical components, gun sights and components, lighting and plumbing fixtures and some automotive parts.
Matte Black Nickel Plating:
Black nickel is plated over matte nickel to give a grayish, non-reflective appearance. It is slightly brighter than black chrome and covers recessed areas better. Since the black nickel coating is quite thin, corrosion resistance is somewhat limited. To improve corrosion protection, the matte nickel may be applied over electroless nickel, but the black color may not hold up in severe environments. It is used for optical components, gun sights and components, lighting and plumbing fixtures and some automotive parts.
From reading other manufacturer's sites, it appears that brushed nickel is always an applied finish, which gets its appearance from a mechanical technique used on the plated product. The nickel can apparently be applied over virtually any metal, as there were examples of brushed nickel over copper shown.
I am the owner of several Kohler faucets (this is NOT an advertisement for Kohler, although I have been very happy with the faucets). Two of them are brushed nickel finish, one is chrome. We have had two of them for at least fifteen years, one of them is brushed nickel, one is chrome. Neither has tarnished, chipped, flaked or in any way deteriorated, despite virtually no care. Neither has leaked. I cannot say whether competing manufacturers offer similar quality levels.