Chrome Plating Feature

By: Paul Tuzson, Photography by: Paul Tuzson

Date: 30.09.2011

Chrome plating

Maintaining mirror-like bumpers and grilles is not as easy as you think.

Chrome plating

Chrome Plating

Brightwork is the correct term for the plated parts on a car. Chrome is just one part of the whole subject but there's so much of it about that it's generally the first thing people think of when they consider plated parts.

However, prior to 1930 chrome plating wasn't used on cars (except by a few pioneering auto makers that adopted the process a couple of years earlier). Virtually everything before then was actually nickel plated. But the open structure of nickel allows oxygen to get in and cause corrosion. Preventing this called for endless polishing and waxing.

Chrome plating is much less vulnerable to the passage of oxygen so it was adopted as a means of protecting the nickel. It still does the same job but these days the chrome gets all the glory. Yet, as the specialists at Melbourne-based Pro Platers pointed out, nickel and chrome are interdependent as far as 'chroming' is concerned. Copper is also an integral part of the process.

A high-quality chrome finish involves surface preparation of the original metal, then copper plating, nickel plating and then chrome on top. To use a painting metaphor, chrome plating can be thought of as a clear coat for nickel. The brightness of the chrome is entirely dependent on the nickel under it.

Harley, one of the specialists at Pro Platers, explained that chrome applied directly over copper is like dull silver paint. It remains dull no matter how much you try to polish it. It's the nickel underneath the chrome that makes it bright and shiny. He also pointed out that the shiny chrome finish on a show car is just that - the finish. Aside from the actual plating, a great deal of preparatory work is required.

KEEPING UP APPEARANCES

The initial step in a good chrome job is the removal of all the old plating. The parts are first dipped in a tank of electrically active sulphuric acid. This removes the chrome and nickel quite easily but the original copper is more of a problem. On zinc die-cast parts there are often areas where the original copper plating didn't reach.

If the parts remained in the acid for long enough to remove all of the copper, the exposed zinc would be severely damaged. Variations in the thickness of any original copper plating can lead to the same problem. In these cases acid is used to strip the chrome and nickel and the copper is removed by abrasion. Steel parts are less affected by this than zinc but it's still an issue.

Well-meaning restorers can cause problems for themselves by trying to remove original chrome/nickel plating by abrasive means. If they make the original plating thin in places, or completely expose the base metal in localised areas, the acid will work unevenly and cause damage to the base metal that has to be repaired.

It's better to remove the chrome/nickel in the acid and take most of the copper off by hand. As we said, care is needed to avoid damaging the base metal. Digging the edge of a sanding disc into the work is an easy mistake to make and will have to be repaired, which obviously adds to the cost of the job.

Many parts are in need of repair right from the start. Often, particularly with bumper bars, some beating is required to remove dents and restore the original shape. This is done with heavier versions of panel-working tools and mechanical hammers and presses. Depending on the type of base metal and its thickness, repairs can be made by welding, bronzing or soldering.

While the processes described so far create a sound base for good plating, the following steps determine the type of finish that will be achieved.

POLISHED PERFORMANCE

After stripping and repairing is completed the parts are polished in preparation for copper plating using various types of abrasive belts and wheels. Copper plating helps bind the following nickel and chrome layers to the base metal, but it also acts to fill small imperfections in the surface of the part.

Preparation for nickel always involves finding a balance between polishing imperfections out or allowing copper to fill them. The exact combination of techniques depends on many things. However, it's no surprise that the highest quality work (which is what automotive restorers need) calls for a very fine surface finish on the base metal. A great deal of time and a series of increasingly fine abrasives and polishing wheels are employed to achieve this.

When copper is applied over the finest surface finish, the foundation is laid for a beautiful final result. However, the copper itself has to be polished. Again, the finest finish creates the smoothest, brightest chrome. This is one area where a skilled customer can have some hands-on input.

While mechanical polishing is often used in production, copper plating can also be blocked back to an extremely fine finish by hand. John, owner of Pro Plating, says some automotive customers like to get their parts copper plated and then take them away and rub them back themselves. "Some of them do an extremely good job - others don't," he said.

Copper plating can be applied and rubbed back more than once and this can be done to build up a virtually perfect finish on a less than perfect part. However, it can only be done perhaps three or four times because the heat created in polishing the top layer can have a detrimental effect on any layers underneath it and undermine the stability of the whole job.

Hand finishing creates much less heat but it's very labour-intensive and expensive. Doing it yourself is obviously cheaper but may cause problems that call for another coat of copper, which is expensive in itself.

After the copper has been polished to the required finish, the part goes into the nickel plating tank. A part requiring the highest quality finish might spend an hour in the solution to build up a good coat.

We don't have the space here to go into a proper explanation of how plating works, but the deeper technical details of the process are more the concern of the plater anyway. Suffice to say that it's somewhat like reforming the lead plates in a battery during recharging. For extremely bright, shiny chrome, the nickel is polished to a very fine finish. After that the part is washed and immersed in the chrome bath for maybe just 15-20secs. That's right! Applying the final chrome finish only takes that long.

SOMETHING DIFFERENT

As we've described, polishing creates shiny parts. However, shiny chrome isn't always what's required. Satin finishes are sometimes employed for their particular look, or to match the finish on existing parts.

When part matching isn't involved Harley explained that the satin finish is usually applied to the base metal. However, any of the layers can be polished in a way that will contribute to a satin finish. Each has a particular effect and can be combined with different amounts of plating to match the appearance of any part.

It's virtually impossible to describe everything that can be done. It's really just a matter of taking your part to a quality plater and discussing your needs.

So, how do you pick a quality plater? Harley explained that it can be difficult.

"The problem is that a bad job on which an operator has taken short cuts can be made to look good. It won't last, but it will still look good initially," he said.

For instance, a part can be directly nickel plated without the prior application of copper. And the tanks themselves are expensive to maintain. There's the cost of the metal, which is considerable, and also the chemicals that must be constantly added, tested and balanced. Samples are regularly sent off for detailed scientific analysis.

Unfortunately, none of this can be seen or checked by a customer. Physical defects in preparation are obvious and can be spotted, but other shortcuts won't become apparent until they've reached a point of deterioration necessitating fresh plating. Let us know how you go getting your money back after a couple of years…

About all a customer can do is make a judgement based on reputation. Hang on to your invoice and if deterioration sets in, go back and try arguing. But even if you win the argument, would you really want the same plater to redo the part?

We can say that in trying to find a plater to work with on this story, the name
Pro Plating (called Prahran Plating until recently - ph: 03 9510 7586) constantly came up among the most reputable sources. Before you start calling platers themselves in your region, we'd suggest calling everyone else you know in the auto game and asking them who they use for plating. You might get a more objective view of who is good by doing this before you start talking to platers themselves.

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