On Wed, 28 Mar 2007 07:44:50 +0700, Bruce
wrote:


I've tried things ranging from purpose made passivating stuff to
vinegar. At the moment I am using a tile cleaner sold, here in
Thailand in every supermarket, that is 20% hydrochloric acid.

One comment I probably should make is that all the passivation
chemicals work by dissolving (eating) some material from the surface
of the piece being worked on. Of course this is how it works, removing
all the oxides and other rubbish from the just welded surfaces. BUT,
it also etches the nice shiny surface of the expensive piece of
stainless you just welded.

My experience is that if you don't polish the etched surface back to a
mirror finish you still get staining.

In another message I mentioned some dinghy lifting brackets I made
that stained. They had been left in acid overnight and were perfectly
clean but with a matt finish when I installed them -- thought the matt
finish would hold the paint better -- wrong.

Bruce in Bangkok
(brucepaigeatgmaildotcom)

Thanks again Bruce,
There is just so much to learn
Peter