Subject: Green copper

From: Eric Kasten
Date: 23 Dec 92 21:17:44 GMT

Ok, here's a question for you folks.  Sometimes on copper metal	
sculptures you'll find a finish which is sort of a rough green
substance (maybe somesort of copper oxide?)  The question is:	
just what is this finish, and just how is it created?  
Thanks for any info!

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From: [email-masked] (Phil OKunewick)
Date: 23 Dec 92 22:39:33 GMT

>just what is this finish, and just how is it created?  

   It's likely a combination of substances.  Corrosion can take many
forms, depending on the corrosive agent.  Whatever free negative ions
are around will bind with the copper and form green, blue, or brown
substances.  Other colors may be possible, but not as common.

   Copper Ore comes in these colors.  Native copper (pure copper
mineral) is always found with a dull colored coating.  Copper nuggets
and crystals are cleaned in a solution to make them shiny, then sold
in rock shops.

   Copper is not a very inert substance; it corrodes easily.  How long
will a shiny penny stay shiny?  But the layer of corrosion insulates
the copper from further corrosion.  The same is true for several
non-ferrous metals, like lead, zinc, or aluminum.

   Copper oxide probably makes up a good part of the coating - copper
and oxygen.  Near salt water there's the potential for getting Cupric
Chloride into the mess, from the chloride ions in the "salt air".
Copper Sulphate could form if there's any sulphur around, like near a
hot spring, an old coal-burning industrial district, or on your
battery cables.  Whatever is around goes into the coating.

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From: [email-masked] (Steve Hollasch)
Date: 23 Dec 92 22:38:53 GMT

Eric Kasten writes:
| Ok, here's a question for you folks.  Sometimes on copper metal	
| sculptures you'll find a finish which is sort of a rough green
| substance (maybe somesort of copper oxide?)  The question is:	
| just what is this finish, and just how is it created?  
| Thanks for any info!

    The finish is oxidized copper (copper rust).  Just take a piece of
copper, roughen up the surface, and either mist it or just let it sit
outside for a while (or inside for longer).

______________________________________________________________________________
Steve Hollasch                                   Kubota Pacific Computer, Inc.
[email-masked]                                 Santa Clara, California

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From: [email-masked] (Michael Moroney)
Date: 23 Dec 92 23:13:52 GMT

>just what is this finish, and just how is it created?  

It is basic copper carbonate or basic copper sulfate, formed from 
oxygen, carbon dioxide and sulfur oxides (pollution) present in the
air.

-Mike

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From: [email-masked] (John Whitmore)
Date: 24 Dec 92 03:24:31 GMT

In article <[email-masked]> Eric Kasten writes:
>substance (maybe somesort of copper oxide?)  

	The name for this kind of patina is 'verdigris'
(check a dictionary for details).

	It is common practice to treat copper roofs with
ammonium sulphate to form the green color quickly; it is not
exactly an oxide, and simple weathering sometimes does not
do the trick.

	John Whitmore

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From: [email-masked] (Morgan Hall)
Date: 24 Dec 92 15:24:03 GMT

>just what is this finish, and just how is it created?  

This group is great!  Thanks for the replies to my questions on anodizing
metals.

There are already several replys on what the green patina on copper is.
I've always heard it called verdigris.  I've tried several ways to make
it form more quickly -- so far:
	1:  mix vinegar and salt.  apply and let dry
	2:  Urine (yup -- collecting is YOUR problem)  Apply & let dry.

I'd guess that strong bases (ammonia, lye) might work as well as various
acids, but I've used the two above.

Morgan

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From: [email-masked] (Adam Karpowicz)
Date: 25 Dec 92 13:32:48 GMT

>>substance (maybe somesort of copper oxide?)  

The copper metal sculptures are actually cast bronze (mainly copper+
tin,etc). In a book "The colouring, bronzing and patination of metals"
by Richard Hughes and Michael Rowe, published by Crafts Council, 1982,
U.K.(ISBN 0 903798 60 3), one of the recipes for cast bronze patination
is:
make a solution ofcopper nitrate+water+ammoni0.880 + aceti?)+acetic
acid(6%sol)+ammonium chlori in 1:1:4:4:1 proportions by weig and
dab on with a soft cloth over a period of five days, rubbing with a
dry cloth after each application to remove loose deposits. This gives
a green patina.
The book emphasizes thorough cleaning/sanding/degreasing before patination.

Never tried it, hope it helps

Adam