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Warning: This procedure should be undertaken with appropriate precautions; goggles,
gloves, protective clothing, adequate ventilation.
As part of a large scale patination project in which I patinated a steel
roof surface 24 by 48 feet on both sides I performed some 40 experiments
to find out how to patinate the steel which was a requirement for structural
reasons. In doing so I also experimented with paint, buying over $350.00
worth of spray paint, eventually finding one single color which for all
intents and purposes is green patina. When placed in recesses and the
high areas are rubbed off it is indistinguishable from a cupric nitrate
patina.
It is a car paint: GM 42, 1980 Chevrolet
Medium Green. While this is ideal for smaller surfaces my paint
experiments did not produce the surface effects I required on the large
scale work. I reasoned that if I could plate the steel with copper and
then convert the copper to patina in a fume not only would the job be
easier but it would also be safer than dealing with solvents or corrosive
patination techniques (such as a cupric nitrate patination) over large
surface areas. I was dealing with 4 x 8 foot sheet steel to be equally
patinated on both sides simultaneously. Other types of objects might be
easier to deal with. 'Tents' of polyethylene plastic sheeting stapled
to a framework of 'economy' studs were built. The construction of such
a tent requires that it be sealed (draped onto the floor from the frame
and then weighted down). The object inside is positioned on supports of
some kind so that it is suspended off the floor in the air inside the
tent. Then pans of household ammonia are placed underneath the object.
The fumes attack copper or copper based alloy surfaces. Under normal conditions
one can activate a copper containing surface with a dilute salt solution
to speed up the procedure and obtain a blue patination but this proved
too corrosive for dealing with steel. The final procedure chosen was as
follows:
l) The steel was cleaned well. Sandblasting would be ideal but was impractical
for the project. Solvents were also out for safety reasons on such large
surfaces without good ventilation. We ended up using Fantastic® cleaner.
Two scrubbings with Fantastic® on large sponges and good rinsings in between
and after were adequate most of the time. The surfaces were then left
damp with the rinse water. Only the edges were handled to avoid contamination
of the cleaned surfaces.
2) A contact plating solution for copper plating was prepared (see
below) and this was applied to the steel using paint rollers (goggles/gloves!)
Brushes work also but the paint roller is a bit more gentle. Plating occurs
instantly. Several passes may be made over the same area, without pressing
hard, which can remove the delicate plating. The surface was then rinsed
very well. If areas of the plating lifted grease residues were the cause
and a further local Fantastic® sponging and good rinsing sufficed to allow
plating to take place. After final rinsing the steel (held by the edges)
was taken to the tent. One moves fast to retain the surface moisture.
3) The steel was then placed in the tent and pans of ammonia enclosed
under it. The tent was sealed. The centers of the thin sheet sagged causing
pooling, therefore we built a wooden support with a single nail pointing
upwards to support the sheet. More stable objects would not need support,
though pooling may be factor to consider depending upon the surface relief.
The time required to convert the copper plating was optimal at about 1-1
and a half hours.
4) The steel was removed and gently rinsed as scrubbing or hard spraying
can remove the delicate patina surface. It will be a mixture of blues,
greens and hints of brownish red where pooling has occurred and the surface
dried. In my case I chose to re-introduce pink spatter marks to the surface
by spattering droplets of the contact plating solution onto the patina
surface where they instantly went pinkish-brown. The steel was then dried
with fans and immediately sealed using clear automobile enamel paint.
I then went back with stencils and gold spray paint to further modify
the surface.
The steps in the procedure are then: Clean,
rinse,plate, rinse, fume, rinse, dry and seal.
The conversion process
The copper on the surface is attacked by ammonia liquid, not as much by
the fume which has a different chemical composition than the liquid. The
water dampened surface slowly takes in ammonia fumes where they are converted
to ammonia liquid in solution so that they can attack the copper. The
purpose of the pans of ammonia below the object is to provide a constant
vapor pressure which replenishes the ammonia on the surface at a constant
rate as it is used up in converting the copper to patina. This system
therefore ensures better overall constant dilution control than beginning
with ammonia on the surface.
Control Factors:
Resists: Resists may be used to prevent plating or to prevent the plating
from being converted to patina by the fumes. Resists to plating may be
a greasy material (litho-crayon, oil) or thinned rubber cement. Other
resists require too much cleaning time and may need solvents for removal.
Resists to patination may be a protective spray through stencils (Pam®)
or thinned rubber cement. Pattern control through resists is easy. Time:
Time is a factor in all fumings. Experiment with various times on sample
pieces to have a palette of process marks (colors, tones, effects) to
choose from. Pooling: Where pooling occurs variations in color will result.
Pooling can be encouraged and controlled by local application of greases
before or during patination and by the position and shape of the object.
Various liquid thicknesses cause surface variations. Sealers: Sealers
will each have a characteristic effect on the surface. I recommend making
a palette of various sealing options over a patinated surface. Examples
of sealers include waxes, oils, lacquers, transparent acrylics, enamels,
varnishes and so on. They often have a tendency to darken the colors on
the surface. I prefer clear auto enamel or Spray-Lac number 1473 professional
Finish Clear Dead Flat lacquer. It is available from Star Chemical based
in Hinsdale Illinois, Deerfield Beach, Florida and Dallas Texas. It is
an industrial quality spray and requires good ventilation. It is very
unobtrusive on a surface. With any spray the surface chosen can be glossy,
like paint (in which case why not use paint?) or shortly after spraying
can be matted down with a cloth pad for better surface control. Other
Chemicals: I mentioned dilute salt solutions earlier. Many chemicals will
modify surfaces. (Remember never to mix bleach and ammonia). Experimentation
and sample making will offer the user control choices. Suggestions for
initial investigations include salt, vinegar, baking soda and local heating.
There are a number of patination books available including one I sell
on patinas for small studios.
Contact Plating Solution Recipe
All safety warnings apply. Always add Acid to Water!! Goggles/Gloves!
250 grams copper sulfate (CuSO4) Technical
grade chemicals for this solution is fine.
42 cc sulfuric acid
Distilled water to the 1000 ml level.
Put about 800cc water into plastic or glass container after marking
the 1000cc level on it. Add the copper sulfate and stir to dissolve. Slowly
pour a thin stream of acid into the swirling water. Heat is evolved-be
aware of this. Rinse the acid container with distilled water and top up
the mixture with it to the 1000 ml level. This solution can also be used
as an electroforming solution for growing copper. Remember, acids are
dangerous. A dust mask is suggested around chemicals. Work cleanly. Copper
salts are toxic and irritant and should be handled with care. Dispose
of properly.
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