Chrome Plated Parts:  Construction, Cleaning and Preservation

by Paul Higley

I have been dismayed by the degradation of some chromed pieces on cars in near regular use and cars sitting awaiting their turn for restoration, even though they sit in a garage and are exposed to neither sun nor rain. Having asked around some on how best to clean and preserve these pieces, I thought I would pass along my observations and see what others can add to the subject. I knew that the wrong solvent on glass can cause cracks to propagate and was worried that the wrong treatment of chrome could accelerate its demise.

Our metal parts are usually either painted or plated to prevent rust or corrosion. Steel parts are mostly iron and if left bare will rust with water contact. Bare aluminum parts with oxidize and form a dull then white powdery exterior when left exposed to the elements. Both materials can be electrochemically plated with other metals less susceptible to corrosion from the elements. When steel parts are chromed they are not just plated with chrome as the chrome will not “stick” well to the steel directly. Usually parts are first plated with copper which sticks to steel, then nickel is plated to the copper as chrome will not survive long when plated on copper. The nickel coating can actually be fairly thick compared to the chrome or copper. Finally chrome is plated over the nickel. Some of the early pre-war cars left off the chrome outer coating and were just nickel plated over copper. Both plating processes involve submerging the part in baths with free ions of either copper, nickel or chrome. An electric current is used to force the metal ions into plating out on the part. The electric current is applied between your part and an electrode in the bath. This means your part needs to have an electrical connection somewhere and at this connection a spot will be visible after plating. It can be attached on the back of a part or in a non-important area. If you have unusual parts plated you might specify where to make the connection or risk a flaw in the plating in the wrong spot. The plating is generally very uniform in thickness and thus any surface irregularities in the part are seen in the final product. Chrome and to a lesser extent nickel are very hard metals and scratches generally cannot be buffed out once they are plated. Copper is softer and some buffing is possible after plating and before application of the nickel and chrome plating. Deeper scratches must be polished out or filled in prior to nickel plating. Preparation of the part for plating is sometimes 90% of the work in plating parts. This is where you can save some money if you can get much of the surface preparation done before handing the part to the plater. The expense of electricity and the metal ions in the bath is small compared to the labor of preparation of you part for a good finish. 

The steps in plating parts are:

Stripping: Plating needs a bare surface so any old chrome, nickel or copper plating, as well as any paint or other coating will need to be stripped. Removal of the old plating may need to be done by the plating house. Polishing : The part needs to be polished to ensure a good finish. Any flaws will be visible in the final product. This is done by sanding the part with various grades of sandpaper, working from a very rough to a very fine sandpaper. For severe pits lead or brass can be used to fill the pits or scratches and then polished.

Electroplating: The standard for chrome plating is triple-plated chrome, which typically means that the part is first plated with copper, then nickel, and then chrome. More steps can be added by applying additional protective layers such as copper, nickel, a second copper coating, a second nickel coating, then chrome. This allows another polishing step on copper to remove blemishes. The copper can be buffed to a brilliant shine and any flaws fixed before nickel plating. There are two types of chrome plating used, hexavalent chrome and trivalent chrome. Hexavalent chrome produces a brighter, show-quality finish; trivalent is slightly darker chrome plating. Hexavalent plating is more dangerous to the people doing the work so most are now using Trivalent plating. The difference is only visible to me if you put one from each type next to each other. The lesson here is to do all the chrome in the same process if you are really picky on the match.

Final Inspection and Buffing: If close inspection shows any blisters, waves or other imperfections the part may need rechroming . This is essential for long-term durability, even the tiniest blister can grow and spread after a few years, ruining the piece. 

Plating Plastics

It always amazed me that chrome could be plated to plastics. If there is interest, I'll look into this more. It is interesting to note that plastic parts can be re-plated and apparently the cost is not outrageous. It's still going to be better to buy NOS if available.

Maintenance and preservation of Chrome parts on your car

The spotting and deterioration of the chrome finish is apparently a result of electrolyte getting into micro cracks or flaws in the chrome plating and causing electrolysis between the dissimilar metals in the plating process or rust of the base metal. The electrolyte in most cases is water or salty water. Battery acid would be a disaster. The goal for preservation of the plating is to minimize any flaws in the plating and to keep anything that could considered and electrolyte out of the flaws. This means water, particularly salty water is the enemy and anything that prevents water from getting to the chrome is the cure. I found a note from The Henry Ford Museum which recommends,

“Clean brightwork once, then protect it with a coating. Every time a metal surface is polished, material is removed, so it is important that the metal surfaces are thoroughly protected to maximize the time between each polishing. All elements to be polished should be removed and disassembled to prevent polish residues from collecting in recesses and to simplify the coating procedure. The cleaning and coating of one brass headlamp can take as long as three days. Use a mild polish such as Autosol, then clean off polish residues with acetone and mineral spirits before coating. Watch out for intentionally painted areas, particularly in stamped lettering. Never use a buffing wheel or any powered abrasive methods to clean brightwork. Nickel-plated surfaces can be very thin and are probably worn thin from previous polishing. Coat all brass and nickel surfaces with an acrylic such as Incralac for the best aging properties. Since this work requires the use of solvents, as well as experience in identifying materials and how to best treat them, consult a conservator. All chromed surfaces should be polished (if needed), cleaned with acetone and mineral spirits, and then coated with a microcrystalline wax such as Renaissance Wax. Apply a heavy coat of wax then allow it to dry without buffing. Use a hot air gun to slowly and evenly heat the part. When the wax begins to melt, spread it around the surface and let the part cool down. The heating process drives off moisture that may be trapped in corrosion pits and allows the wax to flow into these pits to form a sealing plug. After the part cools, buff off the excess wax with a cotton cloth. Only do this to pieces that are away from paint and plastic and can handle the heat from a hot air gun. If there are significant areas of iron corrosion under the chrome, a corrosion inhibiting wax/oil solution, such as CRC-350, should be applied before waxing to saturate and stop the corrosion.”

The consensus of most advice I could find for preservation was to keep the chrome parts clean and dry. Some recommend wax but only if the wax has very low or no water in the mix or it is heated during application. Some groups still say not to wax. I suspect this is due to trapping water under the wax, This is cured by the hot air gun step. I think I will try this. All agreed that the plated surface is not as rugged as it would appear, do not buff the chrome, clean by hand with mild soap and water or Autosol, avoiding harsh cleaners, abrasives and commercial car washes, small scratches should be touched up with clear paint to keep corrosion from getting started. I'm not sure how this clear paint will look but it was recommended so I am passing it on.

There were several groups that reviewed all available cleaners, polishers and clothes for cleaning and polishing and they all seem to agree that the paste form of Autosol is the best cleaner, Silvo metal polish is the best polish and chamois or possibly pure cotton is the best cloth to use on your chrome. I need to get very busy on the '49 Roadster, its chrome is dirty and showing my lack of care. I hope this helps.

 
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