Green patina on copper

Hi, I recently remodeled my bathroom. I had the good sense to hire a
plumber to do the plumbing. Turns out he is a bit of an artist in
addition to his regular job. He makes sculptures, etc., out of copper
tubing. Anyway I was talking about my work as a goldsmith and he
asked me of a good recipe for something to apply a nice green patina
to copper that will be left outside. I didn’t know anything other
than chlorine and I didn’t know how to weatherproof it, if that is
necessary at all. I promised him that someone on this list would
know, no pressure. Thanks for your help.
Mark in Wisconsin, USA

Hello Mark,

The green “oxidizing” process is already a natural kind of patina and
will stay on the copper.It takes a few days (or more depending on the
air humidity)to get oxidized and you don’t have to do anything at
all.This oxidizing process in fact protects the metal (kind of
protection !!)from further deteriorations.Let nature take care about
this nice effect and tell your plumber that this is the cheapest way
of getting the nice green color on his copper.Sure,it takes a while
but it last for a very long time. You could speed it up by using a
mixture of household salt and water making a paste out of it and then
cover the subject with this paste.It’s an other way of using chlorine
and it doesn’t smell so icky!!!

Regards Pedro

I accidentally stumbled on a fantastic green patina on copper. I was
making a trellis for some climbing roses and was using copper pipes
which I soldered together with common old lead solder and flux—just
like the plumbers do. I was not worried about using lead solder as I
was working out doors, and food would never come in contact with the
lead. Well, I am quite good at working with silver solder when
making jewelry, but my lead soldering was a bit messy and I kept
applying flux to keep the solder flowing. the flux dribbled down
the copper pipes, and dried to a beautiful green color. I then
decided to coat the entire trellis with the flux, let it dry and see
what would happen. Voila—it all turned a lovely green. Best of
all the patina is permanent. the trellis has been in my garden for 2
years, braving rain, hail, ice and summer heat, including the
sprinklers saturating it during hott spells. Still, the patina has
retained its great color. Just thought I’d pass this bit of
along. Oh, I also put some of the flux on a copper bowl
which I keep outdoors, and it too has stayed a lovely green
throughout the seasons. Cheers. Alma

    the flux dribbled down the copper pipes, and dried to a 
beautiful green color. 

G’day The main constituent of lead based solder flux is zinc chloride.
This used to be called “killed spirits” in England. It was made by
simply dissolving the perforated zinc that used to be used in old
fashioned meat safes in “spirits of salt” - hydrochloric acid - until
there was no further reaction. It is an excellent flux and I have
used it with iron too, as well as copper and brass. But I suspect
that plain diluted hydrochloric acid or salt and vinegar might work
almost as well. Cheers, – John Burgess; @John_Burgess2 of
Mapua Nelson NZ