Chrome looking a little tited, or in need of full restoration? Here's what you need to know
It’s a black art, chrome-plating, though the basic principle is well-known: a metal component is dipped into chromic acid, and an electrical current used to attract the metal in the solution to the part being plated. The longer current is held, the thicker the plating.
Automotive plating is generally ‘decorative’; softer and thinner than the ‘hard’ plating used for engineering purposes. The best quality automotive plating is triple-plating, which involves three separate stages – copper, nickel and then chrome plating – with plenty of work between each stage. That’s why it’s expensive to have parts rechromed. Cheap jobs won’t use triple-plating, and therefore won’t have a deep shine and won’t be as corrosion-resistant.
Here’s what goes on for your typical chrome-plated part. First, it’s chemically dipped to get it back to the bare, unplated metal, and it’s then machine- and hand-sanded to get it down to a smooth surface – or as smooth as it can be, according to the degree of corrosion, scrapes and dents that the part has suffered.
From that point, the part may have to be repaired, and then it’s simply a matter of how much you’re willing to pay, because serious pitting and unwanted holes can be weld-filled, dents and scrapes knocked out and sections can sometimes even be replaced.
The next step is to prep the repaired surface for plating, using a fine abrasive mop, before the first session of electroplating. For a relatively undamaged part, this is likely to be copper flash-plating, a light application of copper to increase the conductivity of the part, to help with the next plating process. But if the part was badly corroded or damaged, the platers may suggest copper heavy-plating – a thicker application that acts as a filler, smoothing out the surface of the part. If heavy-plating is chosen, the part will certainly be re-polished before the next stage.
Next, the nickel plating, which up to the 1920s was the final finish. This is then polished before the chrome plating is applied, which adds a deeper lustre to the shine. Finally, the part is inspected and polished.
So if you were wondering why you’ve had to pay so much for your chrome, now you know.
Words: David Lillywhite