Regrettable, but if you paint over previously chromed finishes, you should scuff the surfaces with sandpaper to ensure best adhesion. This is why the fork blades on a couple of my French bikes with fully chromed forks beneath their original paint have been progressively shedding large flakes of paint and primer from the upper portions of the blades. There is inevitable going to be some degree of over-plating on any bikes where one or more layer has applied beyond the areas which were intended to be exposed chrome - as on chromed half-stays and forks.
Perhaps some more modern paint under coats and primers are now better for holding against the slick virtually non-porous chrome finish. It would be worth looking into before damaging any existing chrome with manual abrasion. I recall a recent thread about a current translucent paint which someone had applied directly over chrome with very good results. I hope one of the Professional painters can offer some good advice here.
Good Luck
Bob Hanson, Albuquerque, NM, USA
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In a message dated 1/21/2007 2:07:30 P.M. Mountain Standard Time, bikes@msu.edu writes:
Bob,
Since you certainly know the ins and outs of plating, could you pls. offer your advice on the best way to go about repainting a frameset that has paint over full chrome? Your information seems to only apply to metal that hasn't been previously chromed. I have a couple frames like this that I'm considering getting repainted and just want to make sure that I understand what I'm getting into.
Many thanks, Tim Potter Okemos, MI
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Date: Sun, 21 Jan 2007 14:26:36 EST From: Stronglight49@aol.com To: lowiemanuel@yahoo.ca Cc: classicrendezvous@bikelist.org Subject: [CR] Re: fully chromed frames
Chrome is a very durable finish and definitely useful for potentially high-abrasion areas like lower stays and fork blades. The added weight of a chrome finish was probably why we did not often see this on the highest level pro-quality racing bikes since the 1960s.
There are several other reasons why we seldom see chromed framesets today, but they are not entirely extinct. You will still see relatively inexpensive BMX/Freestyle bikes and Low-rider bike frames in full chrome. However, because OSHA has deemed the process to be very hazardous to health and the EPA has very realistic concerns about the final containment of all the highly hazardous chemicals used, these bikes are generally made in third world countries where both workers and the environment may be shown little regard. Regardless of the risks, the companies which do commit to plating OEM frames generally do a good job because they are familiar with working with bike frames and their livelihoods depend on producing consistently good quality output.
Most of the reputable large commercial after-market platers in the US have now removed chrome plating from their offerings. Nevertheless, there are some fine smaller companies which will still chrome plate anything from auto bumpers to bike frames, but you should be sure that they are very familiar with the particular needs of hand brazed bicycle frames - which are not the same as plating simple flat sections of steel.
One of the issues (and I may have read this in the CR archives) is the potential for weakening the bottom bracket if certain precautions are not taken when cooling the finished frameset (a lot of heat is generated during the plating process).
Also, the entire frameset must be completely cleaned by several processes. Organic solvent degreasing, alkaline cleaning, and then finally acid dipping or "pickling" - where the metal is dipped in an acid bath to remove any surface oxides or "smuts" remaining on the steel before plating. And any acid salts which have entered the frame tubes, including through any of the small-heat release holes originally drilled into the stays and fork blades during brazing, will later have to be neutralized.
It is also very expensive to complete a proper triple strate plating process which will commonly consist of first a layer of copper, then nickel, and then finally chrome, and perhaps more than one layer of chrome for a good show quality "wet look" finish. Enamel can hide a lot, but because any imperfections will be very evident and may even be more pronounced when seen through the plating, it is best to wet sand or even polish the base layer of copper, sometimes more than once, before moving on toward the final finish layers. So, it really is a lot of work, especially if you want a visually flawless chromed frameset. And I would not begrudge what may seem like an excessive cost - so long as your plater does a good job.
Bob Hanson, Albuquerque, NM USA
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Tim Potter
Coordinator
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