Copper panels can stand alone if they are smaller pieces
intended to be matted and glazed like paper. It is not recommended to allow large
pieces to stand alone since flexing can cause cracks in the paint.
It is not recommended to use thicker sheets for larger paintings due to the weight. Even
the smaller sheets should have some form of backing when painting
Thinner gage copper sheets should be laminated to
plywood with a polyurethane adhesive
such as Elmer's Ultimate
or Franklin Titebond
to make them extra rigid. These can be purchased at almost any
hardware or home improvement center. Rough sand the underside of the
copper before gluing to provide bonding tooth. Because poly-glues
use moisture to cure be sure to dampen the wood surface with a
sponge before applying adhesive.
The key to painting on copper is your initial steps in preparation
and if they are missed
you'll be headed for serious disappointment. The primary
concern is the green or bluish copper carbonates that form on
copper, brass, or bronze surfaces. If not sealed off from the
elements (no matter how well controlled) this
coating of verdigris, which naturally develops as a form of
oxidation when exposed to air, will block the bond of your ground
eventually causing peeling.
The Dutch masters method was to first clean all
trace of grease or dirt with an alcohol solvent then sand the
surface with pumice powder "in circular motion" and
repeating this cleaning process with solvent to deep clean and provide tooth for the ground.
or denatured alcohol is good for this step. Since sandpaper had not
been invented as of yet pumice powder was used but, a good fine
grade emery cloth will work better. The surface should be
and bright. Any solvent residue or grease left on the surface
including finger oils from handling are contaminants that will block adhesion.
Your final cleaning should be done with a fine grade sandpaper to
remove any solvent residue that may remains then wiped clean only
with a clean dry rag and/or vacuum.
Next the surface gets rubbed with cloves of garlic.
One of the active ingredients in garlic is a cysteine-based
sulfur rich amino acid
compound called allicin. When crushing the clove a
a protein-based enzyme called alliinase is released converting the
compound into a sulfenic acid and is almost spontaneously condensed
down to form Allicin, which bears the typical odor of garlic.
Highly unstable Allicin rapidly converts to other sulfur-compounds
such as Ajoene capable of slowing or preventing oxidation. Allicin and Ajoene are the active ingredients for use with copper
preparation. Allicin rich Cysteine residues play a valuable role by cross linking proteins
with the blue copper proteins found in
verdigris on the surface of copper, where as the proteins containing cysteine will bind
with metals such as lead found in your primer. Acid preparation to a surface to aid
bonding of paint is known in today's painting industry
as etching. Use nothing but garlic after this step. Keep
in mind that every chemical you apply at this stage is reactive so
any spirits you apply after the fact may turn part of the surface
black and/or interfere with the paint bond.
You can crush the
cloves in a juicer to a liquid state that could be brushed on
sparingly and/or rubbed with a clean rag and allowed to dry. You may
also find cold pressed garlic juice in the grocery store in the
spice section. A
little goes a long way here. This treatment is sort of a damp
wiping to treat the surface. Sort of the way you apply wood stain. This is a surface treatment and
may feel slightly tacky or textured when
dry. However, it should not appear as a built up coat of paint.
Garlic contains sulfur compounds which react with copper to
form copper sulfate, a deep blue or blue-green compound. The garlic
juice will also turn green (develop chlorophyll) if exposed to a
change in temperature or if it is exposed to sunlight. Most metals
when etched with acidic compounds will produce a surface color
change. The stains created indicate that you have been successful
with the etching process.
Use of metals as support with glue gesso type grounds
will not generally be successful. Acrylic gessoes as well will
properly to any metal surface. This is why with copper an oil
based white lead pigment primer should be used. There are
hazards to using lead
paints so take all safety precautions necessary. Otherwise it is a safe
paint to use. Because all metals start to oxidize once exposed
to air don't allow too much time between
the dry etched copper and the application of your white lead primer.
If you are familiar with the process of sweating copper
tubing, think of the garlic step as the
flux used . The lead
in your primer is the solder. So in order to get a strong bond cleanliness
and pace are essential. Apply in multiple thinned layers with a hake
or roller in a cross hatched
pattern to avoid sanding. I prefer to skip use of a traditional gesso
surface is already smooth and adhesive enough to paint on if primed
right but this is my personal choice. You can built a gesso ground
if you feel necessary.
From here it would be safe to say that you could paint freely
with any oil based paint or by using a
pre-mixed Maroger's Medium.
Similar oil mediums work well at this point. I favor a copal
varnish resins blended into my oil medium which will be discussed at
another time. Keep in mind
that your panel is intended for traditional thin layered techniques
to take advantage of the smooth surface of copper and that heavy
impasto techniques are contradictive to the use of this support.
Note: In an alternate and modern method of
painting, copper is also an excellent support for painting with
lacquers. Although it is not wise to venture into this medium unless
you are willing mix them from scratch and invest in the proper
ventilation equipment, I have entered this information in case there
was interest. This method would require you to start from bare metal to use a
Self-Etching Primer and then apply one or two coats of
Urethane Primer. The reason for the urethane primer is that lacquers
will dissolve in solvents when dry. You need a cured undercoat in
order for it to prevent the lacquers solvent from penetrating into it.
Urethane Primer has a high solids content so it cures fast and it is
easy to sand to build a durable smooth ground. This painting would
have to be sealed again with a urethane clear coat once completed.
Basic Copper ( light gage rolls)
Copper Components (Sheet & Plate)
Sheet Metal Thickness
Better Bond TC-20™ Copper Adhesive
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