I have done some reading on patination (there's a great British book on the
subject-I don't have the title here.) for copper, bronze and brass.  I also
have CDA data and other references, but none adequately address the
practicalities of field application on broad surfaces of new (red) or
slightly aged (brown) copper.

I found a product just now being introduced in this country called "Nordic
Green", and worked with John Lee, conservator extordinaire in Annapolis,
Maryland.  He figured out what's in it and how to apply it so that it
doesn't just weaken the established patina (if any) nor behave like a
fragile coat of paint.  But he did come away convinced that it can both
mask the raw material to look very much like patinated green copper while
allowing the natural patination process to advance, actually encouraging
the process.  The manufacturer doesn't know the tricks John knows.  Nor
have John's findings been verified over time.

One crucial point is to apply it thinly (like John Mascaro's whitwash
advise: "If you try to do a thick one coat application, the material drys,
cracks and peels").  The temptation is to really lay it on because it looks
better.  Don't.

And while you're mixing up dressings...try a lemonjuice (RealLemon brand
will do) and salt mixture on badly mottled pieces of cast brass or bronze
(like after you stripped off the paint splatters and it still looks
bad...it'll quickly strip it down to a rosy red base so you can start all
over again.  (This is not conservation tested, just my home brew.)  --Rev.
Jim