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What is Hard Chrome Plating?

Hard chromium plating is just chrome plating, but it is applied as a fairly heavy coating (usually measured in thousandths of an inch) for wear resistance, lubricity, oil retention, and other 'wear' purposes. Some examples would be hydraulic cylinder rods, rollers, piston rings, mold surfaces, thread guides, etc. There are variations even within hard chrome plating, with some of the coatings optimized to be especially porous for oil retention, etc.  It is called hard chromium because it is thick enough that when a hardness measurement is performed the chrome hardness can actually be measured. It is not really shiny or decorative.

The plating we do is “decorative” chrome plating and always involves plating nickel before plating the chrome. The chrome plating in decorative chrome plating is exceptionally thin, measured in millionths of an inch rather than in thousandths. It is still a very hard surface, but simple 'anvil' type hardness measurements don't detect the hardness because the anvil just punches through such a thin coating.

When you look at a decorative chromium plated surface, most of what you are seeing is actually the nickel. The chrome adds a bluish cast (filtering the somewhat yellowish cast of the nickel), and it protects against tarnish, and minimizes scratching. But the point is, without the brilliant leveled nickel undercoating, you would not have a reflective, decorative surface.
Chrome plating is hardly a matter of dipping an article into a tank, it is a long involved process that often starts with tedious polishing and buffing, then cleaning and acid dipping, zincating, and copper plating. This may be followed by buffing of the copper, cleaning and acid dipping again, and plating in two or three different types of nickel plating solution, all before the chrome plating is done.

When an items needs "re-chroming", understand what is really involved: stripping the chrome, stripping the nickel (and copper if applicable), then polishing out all of the pits and blemishes, then starting the whole process described above.