Index of Information
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THE PROCESS AND THE ART
OF BRONZE
Bronze, an alloy of copper and tin, first
appeared in the Near East toward the end of the fourth millennium
B.C., there is no accurate record of when the lost wax method
of casting was first utilized. It is believed the earliest
users of the method began with a clay core roughly the shape
of the subject to be sculpted. This core was covered
with wax, and then sculpted to the finished form. Once
the wax hardened it was covered with clay. The object
was baked, hardening the clay and melting the wax. The
space evacuated by the wax was then filled with molten bronze.
Once the bronze cooled and hardened, the clay was removed
and the remaining bronze cleaned and polished.
The basic principle of the process has remained unchanged,
although many new techniques have been developed. The
most significant of which was the use of molds from which
many waxes could be made. As opposed to cold cast bronze,
a plastic-based product with metal flecks imbedded, cast bronze
is a permanent medium. Archeologists have found pieces
buried in the earth for thousands of years. Please
take a moment to view the steps to complete a bronze sculpture.
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HOW TO CARE AND PRESERVE
BRONZE
Bronze can be maintained for years of use and enjoyment
provided some basic care and attention is given to its preservation.
The first step in the care of bronze is to understand, minimize,
or eliminate conditions that cause damage. The second
step is to follow basic guidelines for a maintenance program.
This information provides some information useful in the care
of bronze objects, but we encourage professional consultation
if a serious condition exists. If you feel comfortable
attempting a repair yourself, always test any procedure in
an inconspicuous area first.
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CARING FOR YOUR BRONZE
Since statues made in part or entirely from copper alloys
are so varied, it is not possible to cover all aspects of
treatment in this document. Your first line of defense
will be good storage and/or maintenance.
CLEANING AND POLISHING
If you choose to attempt cleaning your bronze or brass,
and you are sure of the surface appearance you wish to achieve,
some of the following suggestions may help
Stable or painted surfaces should be kept dust free. Vacuum
clean all stable statues regularly, using the nozzle attachment
with a brush. A bristle brush or a toothbrush may help
to raise dust from crevices.
Sometimes surface grime can be removed satisfactorily with
soap and water. We recommend a plain soap in a 3% solution
in water. Use deionized or distilled water, and rinsing is
a very important step. If the dirt you want to remove is very
greasy, "Vulpex" may be used in mineral spirits,
in a 3% solution; rinse with straight mineral spirits.
It is especially important to remove old polish residues,
which appear usually as dark green, gray or white deposits
in cracks.
Calcareous (lime or hard water) deposits may respond to a
10 % solution of regular "Calgon" (sodium) in distilled
or deionized water. Allow the solution to soak into
the crust and then remove by scrubbing with stiff brushes.
Then rinse thoroughly in distilled water.
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POLISHING
Some bronze may have been polished to a bright finish, and
altering original surfaces may reduce the historical value
of an object. As mentioned above, some dark, stable
surfaces may be considered "patinas." Collectors
should be aware of any special finishes, especially lacquers
and patinas, which may determine the correct color the metal
should be, the degree to which it should be cleaned and/or
the degree to which it should be polished. If you come
across any special coating after you have cleaned off the
simple dirt, you may wish to consult with an expert before
proceeding.
If you wish to return a bronze or brass object to its original,
polished appearance, it is usually possible with a fair amount
of elbow grease and a good polishing compound.
Old lacquers must be removed prior to polishing. If
the lacquer is original and in fairly good shape, you may
consider investing in a professional treatment to preserve
it. Lacquer removal is best done with acetone, preferably
by immersion. Acetone is a volatile solvent that should
never be used in a poorly ventilated area. (Please consult
the manufacturer or Material Safety Data Sheet for complete
safety requirements.)
Polishing with a mild abrasive is the only safe cleaning method
recommend. Copper and its alloys are relatively soft
metals. Commercially available "dips" may
contain undesirable components such as hydrochloric or sulfuric
acid which act too quickly and remove more metal than simple
polishing does.
Some commercial paste polishes are quite abrasive and may
scratch your fine metalwork. For statues not suffering
from heavy corrosion "DuraglitWadding" polish may
be somewhat less abrasive than others. Light polishing
may be done using jeweler's cloth containing rouge i.e. "Birk
Cloth", "Hagerty Glove"). A museum-proven,
safe polishing method is as follows
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POLISHING METHOD 1
For most polishing use fine calcium carbonate, CHALK, ("whiting")
worked into a slurry or runny paste with equal amounts of
ethanol (denatured alcohol, ethyl alcohol) and distilled water.
The paste is rubbed across the surface, working a small area
at a time, with cotton balls or clean cotton rags. Detailed
areas may be polished with Q-tips in the paste or with cotton
wadding on the end of a sharpened bamboo skewer. Depending
on the design of your object, it may not be desirable to over-clean
every crevice, as this decreases the overall contrast of the
detailing. It is important to remove all residual polish
with distilled water. Drying may be accelerated by adding
ethanol to the rinse water, or by giving the object a final
wipe with ethanol.
POLISHING METHOD 2
Some statues may not respond to the special treatment outlined
above because the oxidation layers are too thick. For
an admittedly more abrasive method, use "Solvol Autosol"
for general purpose polishing. Test for the degree of
polish you wish to achieve on a small inconspicuous part of
the object. Buff on the polish with a clean rag.
The surface must be rinsed with mineral spirits after polishing
to remove any polish residues. This polish can be recommended
because it contains less ammonia than other commercial brands.
Ammonia can cause long term damage to valuable bronze objects.
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WAXING
For most collectible bronze and brass statues, the best
coating we can generally recommend is wax. Wax provides
a relatively flexible coating that is easily applied and that
can be renewed. It can be used on top of original patinas
and lacquers that you do not wish to disturb, as long as they
are cleaned first. Use "Renaissance" wax,
or other "microcrystalline" waxes in most cases,
because it is inert and will not yellow over time. It
is applied to a degreased surface with a clean cloth, and
buffed out with a rag or bristle brushes (shoe polish brushes
are great for this purpose).
For better adhesion, you may wish to dilute the wax in mineral
spirits or varsol, brush it on, let the solvent evaporate
and then buff with a rag or soft shoe polishing brush.
An alternative, on objects made entirely of metal, is to gently
and briefly heat the degreased surface with a hair dryer before
applying the wax. (Do not try this if heat sensitive materials
such as wood and ivory are nearby.)
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Maintenance material and useful information
MINERAL SPIRITS, LUBRICATING OILS, NYLON SCRUB
PADS:
Hardware Stores
Auto Parts Stores
BRUSHES:
Arts/Crafts Supply Stores
WAXES, VULPEX SOAP, TRITON X-100, INCRALAC:
SOLVENTS (Acetone, Ethyl Alcohol):
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