Subject: Re: Turning copper green

From: [email-masked] (Charles Lewton-Brain)
Date: Wed, 24 Apr 1996 23:46:18 -0600

In article <[email-masked]>, [email-masked]
(James Kirkpatrick) wrote:

> In article <[email-masked]>, [email-masked] (Blake
Malkamaki) writes:
> |>I make copper weathervanes and would like to know if there are any tricks
> |>to getting the green patina on copper besides age.
> 
> See http://plains.uwyo.edu/~metal/patinas.html

Here is some more info for patinating. (FAQ caretakers -if useful feel
free to add to the FAQ-I'm not sure how to offer it so am posting)

GENERAL PURPOSE GREEN PATINA                 Lewton-Brain © 1985

   Cupric Nitrate 300 grams
   Distilled Water   1000 ml (fill to 1000 ml level)
   photo-flo*  1-2 drops (wetting agent)

*One can substitute household liquid detergent or 1-4 drops methyl alcohol.

To make up, place the cupric nitrate in a container, pour in water to the
1000 ml level, add the wetting agent and shake until the cupric nitrate is
dissolved.  Warm water will dissolve it faster.  Use plastic containers
for it with a plastic lid, not a metal one.

The solution is applied more easily to brass but holds a little better on
copper.  It may be used on silver, nickel silver, brass, bronzes, steel
and iron.  It may even be used on gold.  It is a surface covering and
providing it adheres well (mechanically roughened surfaces, copper
containing alloys) and is not used next to skin or to eat from it is a
very good general purpose patina.

As in all metal coloring the end result is greatly dependent on the care
put into the cleaning and preparation of the metal surface before
beginning.  If one wishes to develop a perfectly even patina an absolutely
grease free surface is necessary.  Most problems in patination may be
traced to inadequate cleaning or to insufficient patience in application.

The more time and attention given to repeated applications of the patina
the more even a finished surface will be obtained.  Developing the ability
to produce a perfect finish at will allows one the conscious choice of
various qualities and imperfections of finish.

BASIC TOOLS

Hot plate or bunsen burner and a torch
A piece of steel or thick metal above the burner or hot plate to act as a
device to transfer heat evenly to the flat metal being patinated.
A thick short bristled brush
A stiff scrubbing brush
Pumice or Ajax type cleanser
Newspaper or felt in a plastic container
Spray bottle (if this is used the solution may need to be filtered)
Fume hood
Rubber gloves
Chemical filter face mask

NOTE: good ventilation is a must!!!! 

The use of a fume hood with excellent drawing power is insisted on for
this patina application (if using heat for a quicker approach).  Use
rubber gloves and the face mask.  There is no point to unnecessary
exposure to chemicals. 

For patinating three dimensional objects one can use a torch to heat the
object or resort to the slow application method described later.

PROCEDURE

1. Prepare the metal.  Rub it well with pumice to completely remove the
oxide layer on the surface and to provide small scratches for better
adhesion of the patina.

2. Clean the metal as described in the Appendix to remove greases and oils
>from  the surface.

3. Place the flat work on the heated metal plate.  If the work is not flat
place it on a clean fire brick on a turntable and heat it evenly with a
torch flame.

4. Dip the brush in the solution, wipe it partly dry on the newspaper and
dab it on the metal until it is covered with green.  A better alternative
is to moisten a piece of felt and dab the brush on it to keep it almost
dry when applying the solution.  If one is spraying the solution on, a
light touch is suggested and a large shield constructed around the work to
prevent solution being sprayed over everything.  A chemical mask and fume
hood are especially necessary when spraying the solution on to hot metal.

5. Let it heat up to the point that it turns darker, to brown.  Expose it
to a flame, burning the layer on, turning it black.  Do not heat it too
much however as it may lead to adhesion problems.

6. Using a stiff brush under running water remove as much of the surface
coating as will come off easily and then repeat steps 3-6 until the
surface is covered evenly.

7. When an even black layer is formed repeat the process dabbing with an
almost dry brush (or use a sparing spray) build up the green patina.  When
the surface is evenly covered in green cool it and scrub under running
water to remove all that can be removed.  Repeat this until the desired
thickness and color are reached.  One can build it up extremely thickly
with time.  Again, the more time and care taken in application the more
even the final patina.

An extremely wide range of finished effects is possible.  Perfectly even
green, speckled, patchy, yellowish, brownish, tones of green to turquoise,
rough textured or almost smooth, patterned colors and areas of
reddish-brown are possible on copper.

If any problems in adhesion occur dipping in a mild (2%) solution of
hydrogen peroxide between applications improves its adhesive properties. 
This also tends to give the patina a slight brownish tinge.  Use only
synthetic brushes with hydrogen peroxide solution, if brushed on.

After the final scrubbing and rinsing, dip in methyl alcohol and dry in
the air, with a fan, compressed air or in resin free sawdust.  This last
method is fast and avoids water spots.  Gentle blotting also works.

COLOR VARIATIONS

Yellowish tone:  remove the metal from the heat before the patina turns green.

Brownish yellow on green:  expose the finished surface to a light flame. 
Some experiment is necessary here to obtain even tones of brown.  On
textured surfaces the high areas will turn brown first which may be useful
in emphasizing patinated heavy texture.

Greener:  add a few drops of acetic acid.  Do not add more than a few as
too much may ruin the solution.

Blue-green:  dip in a weak lye solution.

Bluish-green to turquoise:  expose the surface to ammonia fumes or paint
on or wash the surface in dilute ammonia (non-detergent household clear
types are good).  Patina that has been heavily treated with ammonia to
obtain a turquoise color may lose some adhesive strength.  When applying
ammonia do it to cool metal as it will tend to dissolve the patina if
dripped on while it is very hot.  The color may be made to revert to green
>from  turquoise by gentle heating.

PATTERN DEVELOPMENT

Scraping:
Areas in bright metal may be obtained by scraping through the patina
layers.  Paint, inks or gold leaf may be laid into the scraped areas and
lines.  Planned raised areas can be scraped clean leaving recesses
patinated.  Hard felt buffs may be used to high polish such raised areas.

Blue-green (turquoise) on green:
When the base color is satisfactory one can paint or draw with ammonia to
develop blue where the ammonia wets the surface.  The process is
accelerated if the work is warmed slightly.  Several applications on the
same place may intensify the blue.  Depending on the strength of the
ammonia used and its evaporation time a deeper blue outline to the
affected area may be developed.

White (very pale green) on green:
Vinegar (acetic acid) can be painted or drawn with.  After a minute or so
working time it is rinsed off leaving its location bleached.

White (to metal surface) on green:
A 1:2 solution of nitric acid when drawn on the surface will bleach the
patina and if left long enough will eat into the surface providing some
surface relief and the brown of the metal beneath showing through.  Make
sure and neutralize it afterwards with baking soda.

Dark brown on green:
Bleach is painted on.  Where it is turns brown after 30 seconds or so. 
This is accompanied by a nice shade of deeper green that unfortunately
washes off with water and disappears as the patina dries.  The brown
however remains.  If the surface is suspended in bleach a mottled brown
and green results.  When oiled or waxed this becomes darker.  It seems
possible that resists might be used with the foregoing color
modifications.

Green areas with brown outlines:
A pattern is laid out on the surface with water, preferably beaded up
slightly.  A gel made from gelatine and water or a lubricating jelly such
as KY or Lubafax would be excellent for this purpose.  A torch flame is
rapidly played once over the surface and the areas protected by water will
remain green, the exposed areas turning brown.  There will be a brown
outline to the protected areas.

Applied finishes:
Spray applications of acrylic sealers, lacquers, silicone lubricants and
oils may be used with tapes, wrapped string or organic materials as
resists to obtain patterned or mottled areas.

PROTECTIVE COATINGS

The finished product may also have some form of protective coating,
although this patina is tough and not liable to damage if applied
correctly.

Traditionally these would include waxes, vaseline and oils.  Also
available are the spray sealers and lubricants mentioned above.  These
work as water does in intensifying perceived color on the patina surface. 
The exact effect will depend upon the refractive index of the coating
involved, its evaporation rate, viscosity, etc.  One should make samples
with various colors and different coatings for reference.  Oils and waxes
tend to darken the color.  The spray acrylics tend to make the patina
resemble green paint and I usually use them sprayed from a distance for a
thinner more subtle effect.  In general the use of such coatings is for
aesthetic reasons rather than protective.

SLOW APPLICATION METHOD

This is best done outside in the sun in hot dry weather.  The solution is
sprayed on in a thin film and let dry.  A light brushing may be used to
remove loose material between coats.  The process may take a day or more. 
Many kinds of patina lend themselves readily to such a procedure.

FUMING OR SMOKE EFFECTS

This requires a good fume hood or outdoor use.  The patina surface may be
exposed to the smoke of burning leaves, straw or wood to modify the
color.  Burning straw, twigs, leaves, pine needles, resinous shavings,
etc. may be placed directly on the patina or the patinated metal dropped
into burning materials for random or semi-random carbonized effects.  This
can be done to almost all metal colorings including smooth ones.  Tape
resists can be used when smoking surfaces.  Afterwards smooth finishes can
be rubbed with a soft cloth to remove loose soot and a gentle scrubbing
with water may do the same for more porous ones.  If doing this use good
sense and follow fire-safety rules.

SMALL STUDIO AND HOUSEHOLD CHEMICAL PATINATIONS

The oldest traditional method of obtaining green patinas on copper alloy
surfaces was to expose them to urine, preferably aged to develop a
stronger ammonia content.  Works have been buried in manure, coated with
urine containing pastes or sealed in an atmosphere of urine fumes.  I have
heard of a Korean goldsmith who had forty or so jars of aged urine in his
workshop, each labelled with its date and quality, the older ones being
more prized.  While ammonia (presumable more hygenic) works well as a
substitute for urine one would expect that diet and physical condition
would add minerals, salts and complex chemical compounds to the solution
and so affect metal surfaces in more subtle ways than straight ammonia
does.

Burial in alkaline or acidic earths has also been used to create patinas
and may be considered a kind of paste application.  These procedures in
common with others outlined here take time for the effects to develop,
>from  a period of days to months.  Adhesion is not as good as with Cupric
Nitrate patina.

APPLICATION METHODS

As previously, extremely clean metal surfaces give better results.

Cold fuming:
Generally speaking exposure to a fume or atmosphere results in a more even
effect except where condensation causes pooling of moisture on the
surface.  A simple method for doing this is to place the object on a small
platform (to keep it out of the patination agent) in a large plastic
container or bag and pour the agent out on the bottom of the container. 
It is then sealed and left to affect the metal.

Painted solutions:
The solution is painted on with a brush or swab.  It may be necessary to
use a tiny amount of soap or some alcohol in the solution to act as a
wetting agent in order to obtain an even surface.  The metal is allowed to
dry and the application repeated a number of times until the color
development is satisfactory.  Often this may be done outside to aid in
drying and eliminate fumes from the workshop.

Sprayed on:
This serves as a method for obtaining an even or evenly speckled effect on
the surface.  It works well for three dimensional objects.  Again,
repeated applications and time yield the best results.  Keep applications
light.  If using a spray bottle the solutions may need filtering before
use.  In the case of ammonia which decomposes rapidly in air one should
spray the surface and then seal it off from the air in a closed (plastic)
container.

Bound materials:
Where a material moistened with a patination agent comes in contact with a
surface etching, reaction takes place more readily at the point of
contact.  An object can be wrapped in cloth or string to take advantage of
this.  Organic materials such as feathers and plants may be bound to the
object.

If tightly bound they will to some extent prevent surface activation by
the patination agent and their outlines will be visible on the finished
surfaces.  When one binds with dry materials with or without organic
materials and exposes the surface to cold fuming they act as resists and
use can be made of this in developing pattern.  In the case of ammonia it
soon permeates the binding medium and begins etching and reacting with the
surface at the contact points.

Pooling:
If the agent is pooled on the surface it reacts where it is pooled. 
Fingerprints can be used as a grease source to force pooling to occur. 
Pooling will result in a varigated effect as the edges of the puddles will
act differently upon the metal than the centers.

Immersion:
The object is immersed in the solution.  This tends not to work quite as
fast with the agents recommended here but can produce even finishes.  In
some cases (as ammonia on brass) strong etching of the surface can take
place.  Immersion can be used as a method of coating an object with a
solution by dipping it, removing it and allowing it to dry.  This can tend
to produce a concentration of effects where the liquid has run down the
piece while drying.

Moistened shavings
Moistened (not wet) wood shavings or other porous materials work very well
for differential patination/etching of surfaces.  Again, contact points
are the focus of action on the metal and very interesting surfaces are
possible.  Using ammonia or vinegar etching takes place producing texture
as well.  Possible media for this include resin-free sawdust and shavings,
peanut shells, kitty litter, styrofoam balls or chunks, crushed cork,
sisal or other coarse fibers, pine needles, grass clippings, organic
materials such as leaves, feathers and so on.  Use them in a sealed
plastic container to prevent evaporation.  The piece may be shaken up in
them to obtain an even effect.  Rowe and Hughes suggest making a dam of
modelling clay to contain the most media in order to obtain pattern
development or block areas of such effects on a piece.2  It should be
noted in this context that modelling clay has a high sulfur content and
will attack and etch silver while turning copper alloy surfaces black
where it contacts them.  This too could be used in developing pattern. 
The cat box or hamster cage could provide a good medium for patination in
this technique.

RECOMMENDED AGENTS  (For use on copper alloys)

Household Clear Ammonia:  produces greens and blues, olive green on
bronze.  Can produce bright blues with brass especially when used as a
fuming agent.  It affects the structure of brass if left in contact too
long (possibly reacting with the zinc) and the brass may crumble or fall
to pieces with light pressure.  Therefore if using brass and ammonia the
structural elements of the piece should be in copper or another metal.

Vinegar:  produces dark greens, blues and will also affect brasses in the
same way as ammonia.

Salt solution:  Varying strengths of salt solution may be made up and
applied to the metal.  Colors formed include some tones of red on copper. 
Deep green is common.

Dry salt:  This can be sprinkled on the metal surface.  It draws moisture
to itself in a humid atmosphere and will react with the surface over a
period of weeks.  When finished the loose material may be brushed off
leaving a varigated surface of    greens, browns and possible reddish
patches.

Iron filings:  In combination with any of the above they will react to
produce localized dark mottled surfaces.

Combinations:  Various combinations of the foregoing are effective for
patination.  There are also other household chemicals which will produce
patinas on metal.

Nitric acid:  Although not a household chemical most studios have some.  A
strong (1:3) solution of nitric acid will turn copper a reddish-brown
color if left to dry.  If a film of it is maintained over the surface for
a week or so a deep even green is produced.  When ready the surface is
rinsed for a long time in running water and loose material is scrubbed off
with a toothbrush and baking soda solution to neutralize it.  Great care
and safety precautions should be used when working with acids (always pour
acid into water) and cleaning up carried out right away.  If the metal
reacts to release brown fumes the acid is too strong.  Use a fume hood for
this procedure.

RESISTS

Wax, tape or lacquer resists may be used with many of the above agents.

A table of application methods suitable for these chemicals is included in
the appendix.  Protective coating procedures would be the same as for the
previous patina.

-- 
Charles Lewton-Brain
Brain Press, Box 1624 Ste M
Calgary, Alberta, T2P 2L7, Canada
fax:403-283-9053
Email: [email-masked]