"G.Beat" wrote in message
news:naQrc.24177$zw.4857@attbi_s01...

[...snip...] This patina is conductive.

OOPS! Aluminum oxide, or Alumina, is very non- conductive. It is a
ceramic used for as a base high Q circuits at 150 Mhz and above (stripline
and microstrip). It is also what is grown on the surface of "anodized"
aluminum in the anodization process. It is also why aluminum is so hard to
solder. The oxide forms immediately on contact with air. Aluminum is the
most reactive metal.

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Steve N, K,9;d, c. i My email has no u's.