There seems to be a lot of confusion and misinformation and resulting unhappiness over less than desirable results when it comes to having items re-finished with nickel or chrome (or brass) by plating shops. I’ve gathered a fair amount of experience over years, which I hope will be helpful, always with the caveat that I am not a plating professional, so if I’m presenting any glaring factual errors, I’d appreciate the correction.
Plating is like painting. Surface preparation is most important, as is subsequent detailing, and adding layers of plated metal does not magically impart a perfect finish on parts. Because bringing items to an acceptable polish before being plated is invariably a skilled and labor-intensive step, this is where things start to go south. The customer wants low-dollar, the plater needs high skill at minimum wage to please the customer, and that ain’t gonna happen. The speed with which most shops need to run over parts in order to meet price expectations means there’s a high degree of probability your parts won’t turn out as “brand new” like you would expect. The best answer to this is to find a shop that will work with you to allow you to do the preparatory cleaning and polishing yourself between plated layers.
The ideal plating sequence for steel parts is 1. fair polish 2. copper plating and polishing 3. nickel plating and polishing, 4. chrome plating if desired. Brass parts intended to be nickeled or chrome plated do not need the copper plating.
A word about copper plating - there are two processes for electroplating steel with copper. One method is a flash-plating process that uses an electrolyte bath which does not attack bare steel; however, the method is capable only of putting on the thinnest layer of copper. The second method employs an acidic electrolyte which would attack bare steel, but allows the deposition of heavy amounts of copper. The “acid copper” plate can be very useful for the restorer presented with a steel part that has become badly pitted, because optimal applications can be sanded down to level rust pits or other imperfections in steel parts, rather as one would use a primer-surfacer when painting. I have used repeated applications of acid copper to bring the surface of a badly rust-pitted radiator shell (not Ford) back to “new” prior to finish nickel.
Next in the “triple plated” process comes nickel. Whether an item is chrome plated or not, nickel plate is a necessary step, because it is an impermeable layer that will hold the item safe from future corrosion. Chromium presents a permeable layer, but in itself is much harder than nickel, and less prone to “dull” with weathering, thus requiring very modest attention to remain “pretty”. Many shops eliminate the initial copper layer, and plate nickel directly to steel. Proof of the necessity of underlaying chromium with a nickel plate was amply demonstrated on many cars made in 1953 and '54. Most notable was the “bullet” elements of the grilles of '54 Chevvies. The Korean War made for a shortage of nickel, so to stretch allotments, car manufacturers opted to eliminate the nickel layer on bright work in strategic locations - Chevrolet copper plated their grille “bullets”, then chrome plated them. This worked well, copper providing enough corrosion resistance to keep the parts from rusting, but ultimately the copper tarnished underneath the permeable chrome layer, and they turned black. Kids my age will recall this, no doubt.
An interesting nickel / chrome difference is the nature of the two metals. Nickel will not discolor much if used on parts that will become very hot, such as header pipes or exhaust components. Chromium, however, turns blue to purple to shades of brown and orange when so heated.
So far as authenticity is concerned, for the Model T, after the brass era, brightwork was always nickel. Those who can tell the difference generally prefer nickel, which to my eye is prettier, and in restoration I feel authenticity is always a plus. Others believe chrome is “maintenance free” as opposed to nickel, but I’ve never found nickel needed any more attention than to be cleaned - for folks who can’t tell one shiny finish from another, I guess it makes little difference.