[VAC] Re: Acid washing

[Toby Folwick <toby_folwick@xxxxxxxxx>]

okay - I'm going to get into some speculation here,
but this is not a scientific post - you've been
warned.

i think the cladded (pure aluminum) layer is put on
the sheet to protect the lower layers from
deteriorating.  since the lower layers are impure, and
are primarily an alloy designed to add strength, the
pure aluminum on top will take the oxidation "hit" as
it were.  that oxidation is the reaction of the pure
aluminum defending itself against the elements - and I
also understand that the AlClad layer will "throw"
itself (assumably through oxidation) over and into
mated pieces of aluminum.  I don't think the use of
Alclad was for shine, but rather "shine" is a nice
by-product.  if you're using abrasion polishes (i.e.
Rolite, Nuvite) and you were to continually polish the
trailer to perfect brilliance 3 times a year, I
suspect that you'd eventually wear through the AlClad
and be polishing the alloy in short order.  These are
the claims of the people who sell "friction" type
polishes (i.e. green ox, tripoli and jeweler's type
burnishing bars) that these polishes, instead of
grinding off the oxidated material making a smooth and
shiny surface, will actually make the aluminum "flow"
(by heat? or, no - friction) smoothing the surface by
re-mating it with itself - removing less material, and
extending the polished life of the aluminum sheet. 
And to be honest, I buy that.  primarily because I've
seen it in action, and it seems to be a good reason
for jewelers to use friction polish.  It's just that
joe or jane schmo generally can't afford the equipment
to do a job that big once every 2 years.

so, there's my 2 cents for free.

Toby