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Zinc/aluminum-plated sheet treatment to darken finish

I'm a metallurgist by training, and was asked for some help by an architect friend - so I thought I'd check with some real specialists first for a bit of guidance! He designed a house situated in a rural part of northern Minnesota and specified a brand of zinc/aluminum-plated sheeting for the roof. The house was built, but neighbors in the area complained about the solar reflection off of the roof.

So he asked: "Instead of replacing the sheeting with one that has a matte finish, could you recommend a chemical treatment that would darken the sheeting and yet maintain its environmental resistance?"

A tricky question, as the outer zinc/aluminum layer is rather thin (< 100 microns, I think), and it would be very easy to preferentially etch the grain boundaries and thereby ruin the sheeting. ANY SUGGESTIONS?

Thanks,

John Clark McNulty
- San Francisco, California, USA
2003

t-wash or mordant solution is an etch solution used for when people want to paint on a galvanised finish.

daren lamberton
- rossendale, lancashire, england
January 28, 2009