Copper under chrome on '56 Bumpers?

[Patrick Fant]

I always thought that there was a layer of copper under the chrome on the bumpers of these cars.  I just talked to the guys at Dico Products who mentioned that back that far - 1956 - likely the bumper was steel and copper was not the under layer.  Does anyone know actually about the chrome process in 1956 for these big heavy bumpers?   pat fant clc#31723

[Cadillac Fleetwood]

In 1956 Cadillac used a triple plating process.  The steel bumper was plated first in copper, then in nickel, and finally in chromium.  This remains the manner in which these bumpers are properly restored/replated today.

During the Korean War (1950-53), Cadillac, like virtually everyone else, took "shortcuts" in the plating process owing to the shortage of strategic metals, hence the poor quality of chrome plating from that period.

-Charles Fares

[Patrick Fant]

Very very helpful.  Thanks Charles.  There is certainly a wealth of knowledge on this Cadillac forum.  And that's comforting to know... pf

[The Tassie Devil(le)]

To expand on what Charles said, originally the process was Copper, then Nickel.   The actual Chroming cover wasn't introduced till around 1927 as the industry finally found a process that protected the Nickel to stop it constantly tarnishing.

The Chrome plating is a clear hard cover that allows the lustre of the Nickel to shine through, brightly.

What people refer to as Triple Chrome Plating is the three layers of Copper, Nickel and Chrome.

The best finish is achieved by a good solid layer of Copper at the base, then the Nickel, and finally the protective Chromium.   The actual process is very hands-on, and requires some serious polishing of firstly, the steel base, then the Copper, then the Nickel, and the depth of each coating is up to the plater and how long the parts are kept in the "Baths" to allow a good depth of material.

A bad Polisher can ruin a good part.

Bruce.

[LaSalle5019]

The Chrome plating is a clear hard cover that allows the lustre of the Nickel to shine through, brightly.

Bruce, I must differ with you. Chrome Plating is definitely not clear. Elemental chromium is a steel-gray color with a slightly bluish hue. It can be plated over a number of surfaces, including plastic. Nickel plating has a slightly buttery yellow hue which is much more pleasing to look at (at least to me), however, it does start to tarnish after a few years which requires repolishing. Chrome plating has far superior anti-oxidation properties and usually fails due to the substrate failing.

The reason for multiple layers: Think of copper as the primer coat.  It bonds very well and is soft.  It is used to fill in pits/scratches and then is polished out to a mirror finish.  It provides some corrosion protection.  Then comes nickel which is much harder than copper and offers much better corrosion protection.  Nickel is softer than chromium but provides the ability to be polished to a very high, mirror-like, luster that the chromium plating needs as a substrate to to also have that high luster. The chrome coating is fairly thin but very hard and protects the nickel substrate (and sheen) from damage and from oxidizing.

Put a chrome-over-nickel part next to a polished nickel part and you will immediately tell which is which as the color of chromium is certainly different from nickel.  Oldsmobile was the first car manufacturer to use chrome plating on their vehicles starting late in 1925. Most other manufacturers started using chrome plating on their 1928 models.

All the work is in the polishing process. Plating is cheap.

[fishnjim]

There's many tricks of the trade to adjust the finishes during plating.  eg; Chrome can be made in "bright" to black.  Chrome used for wear plating on pistons, too.  So mostly correct but I made hundreds of chemicals for plating.  eg;We operated a chromic acid plant.  Chrome metal and chemicals are fairly expensive.   A diverse topic in itself.   
There's different ways to plate nickel and copper too.   The "std" baths from that period are not even used any more, even if they adhere to "triple plate".   Cost structure has changed.
The EPA rules and technology changed vastly since '56.   I think you'll see changes more in the post EPA plating era >'70s.
Usually, you can see some of the copper (verdigris) on the back side, where the chrome didn't plate in the corners, etc where it didn't "throw" well.   Oxidation usually lifts the chrome/nickel off the copper as a sheet also and the copper is exposed.   

[Patrick Fant]

Thanks for all the well informed analysis everyone.  We've decided to leave the front bumper on the 1956 car where it belongs and instead of re-plating we are going to try to polish out the very light surface "haze" on parts of it and also the very fine scratches on the lower middle section left behind some .0000 steel wool.  The best polish compounds I believe are made by Dico Products with about 5 different grades all needing a rotating buffer to do their work.  I'll report back. pat fant 

[The Tassie Devil(le)]

Be aware that if you go through the actual chrome plating surface, and expose the nickel, you could end up with getting cut on the exposed edges of the chrome surface, and trust me, it is sharp, and unforgiving.

Bruce.

[Patrick Fant]

Aaahhh good point.  We are to go very lightly on it and see if it polishes the hair line scratches only