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Chrome

Posted Oct 29 2009 11:00pm

In 1982 when I began building custom frames in San Marcos, Southern California, I was fortunate that there was an excellent chrome plating business in nearby Escondido.

It was the chrome lug work and other parts of the frame that helped me gain my reputation for beautifully finished work.

This was the same plating shop used by Masi, later used by myself, Dave Tesch, Brian Baylis and other local builders.

What makes a high quality chrome finish is the same as what makes a good paint finish; it is what’s underneath, the preparation.

On a frame like the one pictured above, the whole frame is chrome plated, however, only the parts that will show are polished; the main tubes that are painted are left rough.

First it would be an unnecessary expense to polish these parts, and secondly the rough surface made a better key for the paint.

The parts of the frame that would be left exposed chrome plating were first highly polished. The slightest scratch left by a piece of emery cloth, would show after the plating process.

To achieve the best chrome finish, (Which this is.) the polished steel is first copper plated, polished again, then nickel plated over the copper, and finally chrome plated.

The copper affords the best adhesion to the steel; nickel gives the finish more corrosion resistance, but is yellowish in color. Finally the chrome gives the bright, bluish, almost mirror like finish. The coats of plating are extremely thin, measured in millionths of an inch, rather than thousandths.

Chrome is an abbreviation of the word Chromium, one of 91 natural occurring elements. Chromium is a metal which is not useful by itself; things are not made from chromium. However, it can be alloyed with steel to increase strength and hardness, or used for chrome plating.

Chrome is always applied by electroplating; it is not simply dipped in a tank. Say for example a frame was to have a chrome rear dropout faces, right chainstay, (To prevent chain slap damage.) and a chrome front derailleur braze-on. 

The Fuso Lux frame (Above.) and the John Howard fames were chromed in this fashion.

The frame is suspended in a vat of chromic acid. H2CrO4 with the parts to be plated below the surface, the surface of the liquid acid is agitated to make small waves. Without this there would be a solid line where the plating ends that would show beneath the paint.

Electric terminals are connected to a plating material, either copper, nickel, or chromium and to the frame to be plated. A current passes through the acid solution (Electrolyte.) and molecules of the metal travel through the solution to deposit on the frame.

A frame plated in the manner just described would be plated 2 or 3 inches up the seatstays, to include the whole rear dropouts on both sides, left and right chainstays, and the bottom bracket shell. In addition, the seat tube would be plated up to 2 to 3 inches above the front derailleur braze-on.

Also of course part of the down tube would be plated; it being impossible to immerse the derailleur braze-on without immersing much of the lower portion of the frame.

As I mentioned before, only the dropout faces, right chainstay, and front derailleur braze-on would be polished; the remainder would be plated, but with a rough, less shiny surface.

A frame with chrome head lugs (Picture left.) would have the head tube and several inches of the top and down tube plated.

After chroming in this manner the parts to be left unpainted would be masked with masking tape.

The edge around lug work required some delicate cutting of the tape with an Exacto knife.

If a fork crown was chromed the steering column was masked with duct tape before the fork was placed in the tank so it was not chromed.

Similarly, the bottom bracket threads were protected with a rubber plug.

I would use an etch primer over the chrome; this contains phosphoric acid that etches into the metal and provides a firm key for the coats of paint that followed.

Good chrome plating is expensive; one of the reasons being the high cost of disposing of the large amounts of toxic waste this process generates. Even the water used for rinsing the chrome parts after the plating cannot be disposed of without first treating it to render it harmless.

I remember the shop in Escondido had a low wall, about 18 inches high, built around the plating tanks so any spillage was contained, and could not escape out of the building and seep into the ground.

The chrome plating industry was the first to be regulated for toxic waste by the government, and is still highly regulated. Workers in the industry have to undergo regular medical checkups.

It is not the business I would choose to be in, but I was glad to have access to a good plating shop when I needed it.

 

A more detailed description of theChrome Plating Process can be viewed here

 

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