All About Chrome Plating
How many of us have sob stories about chromium-plated parts? The newly chromed items that went rusty in the first winter; the parts that came back from the platers half the original size and with all the detail ground away; the parts that came back still pitted and grotty; the parts that looked wonderful for a few months until the chrome peeled off…
How do we avoid becoming victims?
First, cheap chrome plating will not last. It’s a highly labor-intensive process involving costly materials, so cutting costs will reduce quality. It’s vital to have other layers under the chrome – nickel at the very least and often copper below that – to protect the steel below from corrosion. The shiny layer of chromium on top is porous and, without a waterproof layer in between it and the steel, its life can be counted in months not years.
When selecting where to get your chromium plating done, don’t choose on cost alone. Only a small minority of commercial platers can re-chrome classic car parts. The majority are platers to manufacturing industry, churning out large batches of bathroom components. Some might offer to do plating for you if business is slack, especially if your items are clean and do not need old plating removed, but beware: they are unlikely to apply the very high level of protection needed under the chrome.
It’s unrealistic to expect platers to achieve a perfect finish when re-chroming items that are excessively corroded – especially pitted castings as used for decorative items on many cars. This material is often eroded away far worse underneath the plating, putting the platers in a difficult position when they strip it. They can polish out very light pitting, but polishing too deeply will lose detail. A layer of copper, which can be built up more deeply than other plates, will help, though only if a great deal of expensive operator time is put into polishing most of it off again.
Re-chroming damaged items requires understanding: the damage may be hard to see on a grotty, dull and dirty bumper but, once it’s been chemically stripped and then polished, dents and twists become obvious. Check components very carefully before taking them in and make sure the platers can make any repairs that are necessary before plating. Even rusted-through components can be repaired by cutting out all the rust and welding in new metal before plating, but it has to be done to a very high standard, so is costly.
Where items have threads that need to be used after chroming, talk to the platers beforehand to get the threads masked or plugged, otherwise they will come back with a layer of metal that will make it impossible for you to use them again.
Where you want to chrome items that were not chromed before, remember that the end result will only be attractive if the item can be polished all over to a mirror finish before plating: the slightest blemish will be magnified when plated.
Chromium plating for the last 65 years has involved the use of highly toxic hexavalent chromium and the only reason it hasn’t been banned is that for some purposes there is no alternative. However, many platers are changing over to trivalent chromium: it’s currently more expensive but is much less harmful to the environment. The only disadvantage for us is that it’s a different color!
Thanks to much development effort, the difference is more subtle now and, if you have all your chrome work replated, the difference may not bother you – but if you’ve had some parts plated with hexavalent, then have others done with trivalent and bolt them on the car side-by-side, the difference will be noticeable.
Until the 1930s, most car brightwork was nickel plated, not chromium plated. Fortunately this process is not only still available, it is actually cheaper and easier than chromium plating as it is applied underneath all good chromium plate anyway. Of course, it needs to stay in the nickel vat longer than if it were to be chromed on top, because you need enough nickel on there to withstand your enthusiastic polishing for many years to come.
Another area promoting debate is that of triple-plating. This is where copper is applied first, often quite heavily, before the nickel and chrome. Most platers argue that this is the ultimate, providing much better protection against corrosion, and even suggest that failing to apply copper first is the reason for plating later peeling off in sheets. However, there are dissenters...
‘Absolute nonsense!’ says Bill Olner of Marque Restore. ‘Copper causes steel to corrode at an accelerated rate.’ This, he says, is the reason that Rolls-Royce and Mercedes bumpers, which were coppered from new, have often corroded into holes. Heavy nickel plating is better, if the surface is good enough. Where copper plating is essential, however, is on items which otherwise would be eaten away when put in the corrosive nickel and chromium solutions.
Once you’ve got it plated and it’s looking stunning, look after your chrome. Avoid chrome polish, which is too aggressive: use wax polish as you would for paintwork. Severely corroded chrome work can sometimes be brought back surprisingly well, however, by rubbing with extra-fine steel wool, as the corrosion is from the steel underneath which spills out through microscopic holes in the chrome; then apply a liquid rust convertor such as Jenolite, leave for a few minutes and wipe off before polishing, and afterwards keep it very well waxed for protection.
Published Dec 7th, 2015