chrome pitting

[roger crabtree <rcrabshish@xxxxxxxxxxxx>]

OK, now I know why.  Now how do I get them off the
chrome parts?  I have used Mothers and other products
without good results.  Does anyone on the list have a
good idea?  
RC Billings Montanaaaaa
 --- James <nyb@xxxxxxx> wrote: > The why's associated
with pitting are not exactly
> straightforward, but 
> here are the basics:
> 
> A pit results with the development of a local anode
> where the metal is 
> oxidised (loses electrons).  Electrons from the now
> oxidised metal atoms 
> travel through the metal to a cathodic area where
> water is reduced 
> (gains electrons).  The metal ions formed in the
> process can either be 
> simply washed away, or they may be carried by water
> to the cathodic site 
> where they can join up with the products of water
> reduction to form an 
> oxide.  In the case of iron this is why you find
> orange deposits off to 
> the side of the pit. 
> 
> What causes a site in the metal surface to become
> anodic has a lot to do 
> with the metallurgy of the metal in question.  Pits
> often form at stress 
> points, areas containing impurities (in stainless
> steels sulfur is a 
> frequent culprit), and because alloys are never
> truly homogeneous some 
> parts will simply oxidise more easily than others. 
> Pits in chromed bits 
> and pieces may also start in areas where there are
> flaws in the chrome 
> plating, including microscopic cracks, that can
> expose more easily 
> oxidised metals underneath.  Chromium itself is
> pretty corrosion 
> resistant due to the formation of a thin oxide layer
> that acts as a 
> barrier, the same principle goes for aluminium. 
> However, scratches and 
> other damages (including rocks that hit headlights)
> that result with 
> time can both expose what lies beneath, and perhaps
> more significantly, 
> create areas where water can collect.  Even if your
> car doesn't get wet 
> too often, or the pitted part is inside the car,
> don't discount the 
> presence of water vapour in the air. 
> 
> As for prevention, as stated earlier, a lot depends
> on the manufacture 
> of the metal.  However, keeping the car dry, clean
> (acids in "dirt" can 
> acclerate the process), and trying not to damage the
> metal will help.  
> Polish as necessary, but keep in mind that every
> time you do that you 
> add more little scratches.  You also remove the
> aforementioned oxide 
> layer, making the metal form a new one, reducing the
> amount of metal in 
> the metallic state, although this is a minor point.
> 
> James
> 
> Captden30@xxxxxxx wrote:
> 
> > i was polishing the headlite rings from my 53
> imperial, which has some 
> > pitting. i became curious as to why these pieces
> "pit" and what 
> > exactly is pitting. we all know what it looks
> like, but what is really 
> > the root cause. i would assume that age is a
> factor, but i also think 
> > it is more than that. the piece is made out of pot
> metal, and what is 
> > that made of and is that a contributing factor to
> pitting? i suppose 
> > the why's dont matter that much, but perhaps we
> can better prevernt 
> > our cars from getting future pitting if we know
> the answers. i know 
> > that there are many people on this site who can
> shed light on this 
> > subject.  thanks,  dennis  53 imperial[for sale]
> 
>  

=====
RC Billings, Montanaaaaaa 

http://www.imperialclub.com/temp/1955/RogerCrabtree/ 


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