Re: Guilding on copper

Martin Brown wrote:

Help !

I am trying to find the best way to gild an antique weather vane on
top of an old listed building. At present the finish is 1980's black
Hammerite, but after part of the thing fell off we found that
underneath the black paint was a gilded surface on top of copper
metal. We had planned to just polish it up to bare metal and use
hitech yatch varnish instead. It is a long way up so we will only get
one chance at this. Scaffold is up and clock is ticking.

However, after finding the gold finish someone asked how hard would it
be to restore it to the original appearence (this thing sits on a
Grade II listed building). I offered to find out. The cost of
materials doesn't look too bad and I have access to clean room and
laboratory cleaning kit for surface preparation. The shape is
relatively simple and mostly flat with a few cutouts in it (the
initials of the guy who comissioned the building). There is no way we
could afford to have it professionally gilded - it is all the charity
can do to raise enough money to keep the roof on.

The professional gilders I have talked to have suggested that the best
process for an exterior gold finish on copper goes along the lines of:

Clean surface with fine abrasive.
Degrease.
Zinc phosphate primer
Oil based gold size
Gold leaf heavy transfer
Gilders mop

Bearing in mind that this thing has to survive about 60' up in the air
outdoors and is on a very windy site. How long is such a finish likely
to last? And is there any risk that the zinc phosphate primer (which I
suspect is their recommendation for *all* metals might in time react
with the copper to compromise the surface integrity).

Is there any merit in applying a sacrifical overcoat of yatch varnish
afterwards ot is the gold once attached to the size sufficiently
inert?

I also found an old classical recipe using mercury as the binder for
gold leaf known to the ancient Egyptians which sounds like it would
fall foul of COSH regulations. I doubt that it would be acceptable to
use this method now.

There are also various gold paints, but they look to have limited life
expectancy in such a harsh environment. One thing in our favour is
that noone will be able to look closely at the surface finish!

So can anyone give me any hints about how difficult this would be to
do in practice?
It will fall to me to clean the thing and apply the gold so if it
fails after a couple of years it will be my fault.

Thanks for any hints of practical advice.

Quality marine varnish (e.g., tung polyurethane) degrades in sunlight
over a couple of years. One expects the best solution to be a proper
base layer followed by vacuum deposition. Next best is probably gold
leaf and a suitable adhesive (architectural gidling of domes and
statuary),

http://www.aviewoncities.com/boston/statehouse.htm
<http://www.scholarsresource.com/images/thumbnails/192/a/arc0407.jpg>
Boston
http://www.central-vt.com/web/sthouse/index.html
Vermont
http://en.wikipedia.org/wiki/Georgia_State_Capitol
Georgia

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2
.

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