New Zuiko 17mm f1.8 posted on DCwatch site

Started Sep 17, 2012 | Discussions thread
Antony John
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Re: Silver paints will CHIP + SCRATCH, look very ugly after 1-2 years
In reply to Anders W, Sep 19, 2012

Basically all 'reactive elements have an oxide coating - they're the ones not found in nature as a raw element - you can contrast this with say Gold for instance which is found in it's elemental state, not an oxide.

Basically you can't stop reatcive elements 'reacting' in the Earth's atmosphere with water or oxygen.

In anodising one removes the oxide coating and impregnate the pores with a colourant. that's why you can get black, pink, basically any colour you have a colourant of. As mentioned, once the pores are saturated one seals the surface by forming an oxide layer.
Thus the colourant is impregrnated within the metal and not a 'coating' as such.
The thickness of the anozising is controlled by the process used.

Aluminium (because of the oxide layer), along with any other non-reactive metal, is difficult to succesfully coat. The inertness of the layer (Aluminium oxide in the case of aluminium) alows only physical rather than chemical adhession of the coating system. To succesfully (debatable point) coat aluminium one needs to use a special coating system incorporating special fillers/adhession promoters. The colour of which will depend on the system used. Thus the initial coating is actually a primer and must then be coated with a finishing coat of the desired colour. One way or another these systems will still scratch and chip.
Anozising is the better route, although not perfect.
HTH
--
AJ
Carpe diem quam minimum credula postero

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