Electroplating can be defined as the deposit of a very thin layer of metal onto a base metal in order to enhance or change its appearance. Unlike painting, where the new deposit is sprayed on, the chrome (and associated materials) are applied through the use of an electrical current, hence the term ‘electroplating.’
A plating bath is the name for what is essentially a giant tank, many of which are used throughout the chroming process. The baths are filled with a liquid that contains the desired metal dissolved within it — which could be silver, gold, nickel or another metal.
The plating–bath solution serves as a conductive medium, utilizing a low DC voltage. The metal item that is to be plated is submerged in the plating bath, and a low-voltage DC current is applied to the bath.
The electrolytic process then causes the dissolved metal ions to attach to the surface of the metal to be plated. The thickness of the electroplated layer is determined by the time the item spends in the plating bath while the current is being applied, and the amount of current used.
Sometimes the shape and contour of the item can affect the thickness of the plated layer. Metal objects with sharp corners and edges will tend to have thicker plating on the outside corners and thinner plating in the recessed areas. This is due to the corners being more exposed, therefore attracting more particles.
The Price of Plating
The price of electroplating services is determined by numerous factors such as the type of metal used for plating (i.e. gold, silver, chrome, etc), the desired thickness of the plating, the base metal (i.e. steel, copper alloys, aluminum), the rough dimensions of the object to be plated, and the number of items to be plated. As an example, nickel costs around $16,000 per tonne — as a rough guideline, on the average ’50s US classic car, around 12kg of nickel is used.
What many forget, however, is that since the plating process does not hide or mask surface imperfections, plenty of preparation time is required to ensure a flawless finish before the plating process itself has even begun.
Most vehicles of the chrome era have more than their fair share of dents and scrapes in the trimwork, and removing them is not a straightforward task. Indeed, it’s one that involves plenty of skill, and an even greater amount of time — which all adds to the cost involved, in the same way that panel beating and preparation add to a paint job.
Ask anyone who’s had a bumper from a ’50s US cruiser chromed how much work was involved in getting the bumper straight and tidy prior to plating, and you’ll soon see where a large proportion of the final cost goes — yet it’s amazing how many seem to forget all about the preparation time when it comes to settling the eventual bill.
It also pays to remember that as each tank used in the electroplating process has a current sent through it to activate the solution within, the monthly power bill for the plating business can be as high as $30,000 — another cost that most of us would never even have dreamed about.
Next the old chrome is removed in a cold caustic bath, this time electrified to 12 volts with a reverse charge. That sees the old chrome come off the item with surprising ease in just 10 minutes. The old chrome and stripped metals are not recyclable. Getting rid of them is a major expense for any electroplating company, and it’s controlled by local council by-law requirements (under trade waste consents legislation).
9That next bath is a two-minute dip in a cold cyanide solution, in which the parts are electro-cleaned by having a reverse charge passed through them. Again, a fresh water rinse is performed prior to the next stage. The items must not dry out before being transferred to that next stage; if they do, blotching will occur, often the sign of a lack of care during the process. Thankfully, George and his team check the items at every stage, ensuring only the best-possible finish is supplied to the customer.
A cold bath of 10 per cent sulphuric acid is then used for two minutes to give the surface a key for the next step to etch to. This is essential to ensure that the cyanide-based alkali copper used next will adhere to the item as much as possible. Attached to the sides of the bath are baskets with blocks of pure copper (anodes). When dissolved in the solution, the particles are attracted to the positively charged item, and soon a thin coat of copper covers the whole thing. The copper is less than one micron thick, and acts as a primer-sealer to key-in the next layer of plating.
Again the item is rinsed, then dropped into a 10-per-cent acid etch for 10 seconds, followed by a further rinse.
So far, the compounds used in the process are relatively low cost. But the nickel sulphate the items spend the next 60 minutes sitting in is notably more expensive, in fact, it’s the dearest consumable of the whole procedure. After 60 minutes with a six-volt current, a 45-micron coating will be applied to the item. This is the most important part of the whole process, as it’s the nickel that gives the finished product its shine. Often the difference between cheap chrome and good chrome is the amount of time the items sit in this bath for. The difference is noticeable to the naked eye by the depth of colour in the finished item.
A rinse then removes any excess residue and prepares the item for the chrome itself, which is a comparatively cheap and quick part of the whole procedure. Despite being orange, the chromic acid is what gives the bluish look, and after just four minutes in the bath with a 12-volt current, a three-micron coating will be fixed to the item. Again, the balls in the tank are there solely for insulation purposes. The tank itself is tested twice daily for correct chemical levels, brightness and condition, and is stirred throughout the day. After all, the chrome is a heavy metal, so it tends to sink to the bottom when left for long periods.
A full refill of all the tanks would set George back around $365,000, but thankfully they don’t require complete replacement all that often.