Chrome Plated Pot Metal Trim Pitting and Preserving Question

[wdills]

As we all know, the original pot metal trim on our cars gets a lot of pitting with age and needs to be re-plated to look good. My question is why. Was there something about the original plating process that contributed to this? Is the modern triple plate process better and will it hold up better over time? Or will my fresh, re-plated trim parts show pitting once again in 40 or 50 years? Is there anything I can do to prevent the pitting from happening again?


Thanks
Wayne

[RadioRoy]

The most important thing you can do to prevent pitting is to keep the piece clean and dry. Paste wax will help. The dirt holds the moisture in the air and the constant moisture helps make the pits.

[wdills]

I was thinking about a direct to metal clear like this POR-15 product applied to the back side and the shiny side.

http://www.por15.com/GLISTEN-PC/productinfo/GPCGG/

I was thinking this might protect the part and seal out moisture. Thoughts?

[rockne10]

Pot metal is porous. Porous metal, by definition, allows air transfer. Air includes humidity. Trap humidity in your casting and you are inviting oxidation from its interior. Poor quality plating invites the deterioration quicker. Quality plating, and periodic waxing can make your trim last indefinitely.

[jlmccuan]

Not sure what you mean by "modern triple plating." The process has pretty much always been normally nickle, copper, chrome. If anything, replated pot metal will show pitting sooner than the original. Different metals use differing ground coats, but the processes are pretty much the same with the exception being wartime plating. Grinding off the top layers of pits does nothing about the pockets lurking below the surface, just like they were originally, but now with age. In addition, any pits not completely removed will blister very quickly. Thicker plating just makes the eventual pop off bigger as the corrosion creeps under the plating.

[62champ]

Is there something about the plating process that causes pot-metal to pit? Cannot remember seeing a painted piece of pot metal that had pits in it.

Had a '59 Ford Galaxie with the chrome across the back of the trunk from backup light to backup light. It was a 40K car in excellent shape all the way around, but the back end had been near a garage door all its life with small windows. It was so pitted you could have used it in a saw mill to grind the bark off trees...

[Corvanti]

Wayne, i'd think the body side of the pot metal would be where i would use the Por-15 product - since once it's on the vehicle, it would be hard to "service". i've used their products for rust on the underneath portions of several vehicles and the gas tank product for the Avanti and liked the results. all surfaces were properly "prepared" prior to use.

if you decide to use the product on the visible side, i'd like to know if it worked well for you. in the meantime, i'll use paste wax on the '51...

[oldsalt]

You can plate chrome directly to mild steel, pot metal and a lot of other parent metals but chrome plate is 'porous'. Sad but true. Nickle is capable of completely plating [and protecting] other metals such as pot metal without the tiny holes that are a fact of life with chrome. If the pot metal has surface pits it is because the nickle under the factory chrome plate has finally broke down and allowed the copper and then the parent metal to corrode.

Chrome is just the 'shine', nickle is the protection.

[TX Rebel]

Chrome plating

You can plate chrome directly to mild steel, pot metal and a lot of other parent metals but chrome plate is 'porous'. Sad but true. Nickle is capable of completely plating [and protecting] other metals such as pot metal without the tiny holes that are a fact of life with chrome. If the pot metal has surface pits it is because the nickle under the factory chrome plate has finally broke down and allowed the copper and then the parent metal to corrode.

Chrome is just the 'shine', nickle is the protection.

The aluminum/zinc alloy used in making die cast parts corrodes sacrificially when in contact with nickel. This is why unplated die cast parts, like '62 GT side grills, seldom have any corrosion while plated parts can be badly pitted on the same car. Having a good barrier of copper between the base metal & the nickel helps, but any time that oxygen & moisture are present, the corrosion process can take place. Cars in arid climates will have nice chrome after 50 years, and cars from humid climes will show deterioration of chrome plating after only 5 years. I store plated parts in a dry place, usually my attic. I have an acquaintance who coats all chrome parts with grease when the cars he owns are not going to be used for a while. It is messy, but really helps. All corrosion must be removed prior to plating because you can not plate rust or corrosion. Even tiny pores in the base metal can cause ugly blisters in the plated finish. Do not be shy about asking your plater how long he places your parts in the nickel tank. A plater who hurrys the process by only giving a piece 20 or 30 minutes of nickel will give the type of job often seen on cheap reproduction parts, and the finish will not last long. A good job means at least an hour in the nickel tank, followed by a quick dip in the chrome tank. Also make sure he has a cyanide copper tank for your die cast parts, and that he puts a sufficient amount of copper on the piece. Plating costs have jumped up this year, so be prepared to pay more than you are accustomed to for quality plating. I have received several calls recently from customers who have had sticker shock from their platers.

[studegary]

I paint the back of rechromed parts with something like Rustoleum aluminum and keep a coat of paste wax on the front surface. This has worked for me (parts look good after 40 years). Of course, if you have a poor quality replate "all bets are off".

[gmax336]

During the Korean Conflict there was a shortage or copper and plating was not as good as it could have been during that time. At least that's what my dad's been telling me for the last 50 years.

[jnormanh]

So many posts, so much old wives tales and misinformation. Zinc die cast parts (please don't call them "pot metal") are made by injecting molten zinc into steel dies.The alloy is mostly zinc with a bit of magnesium (no aluminum). Zinc is a reactive (with oxygen in the presence of water) metal, so needs to be protected with a more corrosion resistant surface, namely nickel. Usually the zinc is first plated with a thin layer of copper which temporarily protects the zinc from attack by the acidic nickel plating solution.The quality of the nickel plating (thickness and freedom from porosity) determines the corrosion resistance. The chrome player is very thin, and serves only to prevent tarnishing of the nickel.

Zinc die cast parts can resist corrosion for a long tme ( early Mustang tail light bezels) if done well. Done poorly corrosion may take hold in months.Poor quality porous castings, sloppy molding techniques, poor surface prep, thin or porous nickel = corrosion.

By the tme you notice it, the underlying is seriously corroded.

[Lark Parker]

I paint the back of rechromed parts with something like Rustoleum aluminum and keep a coat of paste wax on the front surface. This has worked for me (parts look good after 40 years). Of course, if you have a poor quality replate "all bets are off".

I agree. (You saved me some typing.)

[oldsalt]

The aluminum/zinc alloy used in making die cast parts corrodes sacrificially when in contact with nickel. This is why unplated die cast parts, like '62 GT side grills, seldom have any corrosion while plated parts can be badly pitted on the same car. Having a good barrier of copper between the base metal & the nickel helps, but any time that oxygen & moisture are present, the corrosion process can take place. Cars in arid climates will have nice chrome after 50 years, and cars from humid climes will show deterioration of chrome plating after only 5 years. I store plated parts in a dry place, usually my attic. I have an acquaintance who coats all chrome parts with grease when the cars he owns are not going to be used for a while. It is messy, but really helps. All corrosion must be removed prior to plating because you can not plate rust or corrosion. Even tiny pores in the base metal can cause ugly blisters in the plated finish. Do not be shy about asking your plater how long he places your parts in the nickel tank. A plater who hurrys the process by only giving a piece 20 or 30 minutes of nickel will give the type of job often seen on cheap reproduction parts, and the finish will not last long. A good job means at least an hour in the nickel tank, followed by a quick dip in the chrome tank. Also make sure he has a cyanide copper tank for your die cast parts, and that he puts a sufficient amount of copper on the piece. Plating costs have jumped up this year, so be prepared to pay more than you are accustomed to for quality plating. I have received several calls recently from customers who have had sticker shock from their platers.

The price of good plating is going to increase... and sometimes you don't get what you pay for. I do my own small parts because: 1. Bad experiences. 2. Cost. 3. Time [I can do it today and put it on the vehicle tomorrow]. 4. It is a 100 mile turn-a-round to get to a plate shop from here. 5. LOST PARTS! [????]. 6. I'm a crazy old man. The pic is my hobby plating set-up in my basement. I'm definitely not a professional but I get good results after a severe learning curve that took several years. I know you are 100% right about the thin coat of nickle that will work OK..."for a while" that is tempting to "get by with". I use .05-.06 amps per sq. inch and nothing less than 60 minutes...I don't recall the build-up but if any light polishing is required that time is a minimum.