I just saw this site on Wikipedia. about anodyzing metal:
http://en.wikipedia.org/wiki/Anodizing
It included a paragraph on "Hard-coat" anodizing cylinder bores in alu blocks. The instance they used was in BMW engines. I assume that this same process is used by Mercedes, and maybe all the way back to Chevy's very peculiar foray into the future with the Vega engine. Anyway, it's a clearly-written brief description, if anyone has been wondering. Like anything in Wikipedia, there's no guarantee that it's correct.