It seems you folk once again need an education on the chrome process
When the plated part is originally fabricated, it is usually a die cast piece made from a Zinc-based alloy (ZA3 grade works the best, ZA10 is virtually unplatable). Even with a high pressure die cast machine (more pusing of the metal through the die than with typical die casting process) the metal flow carries tiny bits of debris, air or "gas" through the die creating sub surface pockets or caverning that can normally only be detected with X-ray or other equipment. Over the course of time, the metal breathes (so to speak) due to the impact of summer heat and winter cold. These pockets try to "escape" so they generally work their way towards the surface. When they break through the metal surface there is little resistance to the microscopic layers of plating process and you get "pitting" each time a pocket breaks through.
Before you attempt to replate a part the piece should be stripped (either chemically or by careful griding by an experienced, trained operator) of the old plating material and down as far as possible to get a smooth surface with no dips or bumps. The good plater will then start the copper buff/copper strike method of plating using HEXVALENT chrome rather than TRIVALENT (the latter works well for things like faucets but does not stand up to the weather and is not the real shiny stuff).
After the copper strike as a base, the part is carefully buffed by an experienced, trained operator. He (or she) gets the copper warmed by the friction of the buffinbg wheel and it can be spread to further smooth out all surface issued and even fill in some of the new pits. After that the hexvalent chrome is attached by electroplating process wither the material is literally bound tightly to the copper base. The thickness of the chrome level is less than an eggshell. The chrome is then buffed out by an experiuenced, trained operator to get it to an agreed to standard for lusture and overall quality. That often is good for at least several years before the chemical reaction I described earlier creates a new crop of pits and you have to start all over.
The EPA requirements on chrome platers (especially those using "hex" chrome) are stringent and ridgidly enforced. Hexvalent chrome is especialy toxic and needs to be accounted for to insure stuff does not get spilled, dumped or otherwise disappears. The cost of maintaining the plating system and the cost of the materials used (especially copper as you have to fill the vat the part is dipped in) continues to rise. The little guys were driven out of the business over the last 20 or so years & the survivors are for the most part platers who do large scale work (like wheels for cars and trucks) because of the cost of making the special brackets and hangars that hold the parts in place during the various stages of the plating process. Like so many things, the unit cost of materials and labor are not all that much but the set-up charges can be a killer.
Jack Mueller
Quality Improvement Manager
Kentucky Decorative Metals (KEN-DEC) October 2000 - December 2006
Customers included General Motors P&A, Honda of America, and Whirlpool Corporation divisions
