How Bronze Sculpture is Made
Just how "original" is a piece of bronze sculpture?
By observing the process of creating such a piece, either one-of-a-kind
or one in a limited-edition series, it becomes clear that each
Dating back centuries, the lost-wax method of
casting is used by New Mexico's world-renowned foundries to realize
bronze sculpture in a wide variety of images from Indian and
western to impressionistic or abstract.
The process begins with the artist's original
piece sculpted in clay, wax, wood or other material.
Rubber mold pulled from original
The "embedded mold" method begins with the
original sculpture being halfway embedded in soft water clay.
Silicone rubber is meticulously painted on the exposed half;
then a plaster shell is fashioned over the hardened rubber. The
piece is turned over, the clay removed, and the second exposed
half is painted with the synthetic rubber and covered with a
plaster shell. This method produces a rubber mold in two easily-separated
halves which can be pulled away from the artist's original without
causing damage. The completed rubber mold, a "negative" version
of the artist's "positive" original, becomes the new master from
which all copies in an edition are made.
The next step creates the second "positive" in
the process: a wax duplicate of the artist's original. First,
the interior of the rubber mold is painted with molten wax; the
halves of the mold are then put together and the hot, liquid
wax is "slushed" into the mold. The wax cools from the outside
inward. When it cools and hardens to a thickness of 3/16" to
1/4", the excess wax is poured out. The rubber mold can then
be opened and the wax duplicate removed. (The mold is then carefully
stored in preparation for repetition of this process for each
piece in the edition. When the final bronze in an edition is
complete, the rubber mold is destroyed.)
At this point, the artist usually returns to
inspect and correct the wax model. Hours, and perhaps days, of
painstaking dressing (correcting) the wax assure faithful reproduction
of the original. A unique edition number is incised into the
wax at this stage (e.g. 2/10 means that this piece is the second
casting in a total edition of ten.)
Next, a wax funnel is added to provide an entrance
for the molten metal. A series of wax channels, or sprues is
attached to provide a path for the liquid metal, and for air
to escape, assuring an even flow of metal to all parts of the
mold during the pouring (Figures 4, 5).
The next step in the process resembles battering
and breading a piece of chicken! The sprued wax Figure is dipped
into a viscous ceramic solution. It is then rolled or dipped
in fine sand which gives detail, and then in a coarser sand which
gives strength. This is repeated until the layers produce a strong
ceramic mold about 1/4 inch thick-creating the second "negative" in
Once hardened, the ceramic mold is heated to
1500 degrees F and "burn out" occurs. It is here that the wax
is "lost" — in French, cire perdue — and,
in the process, the mold is strengthened.
Placing sprues or channels
Molten bronze, an alloy of copper, silicone
and manganese, is poured into the mold. After the bronze has
cooled and solidified, the mold is broken open, discarded, and
the casting--the final "positive"--is removed. Refining this
raw piece is a delicate and demanding process that includes removing
rods of bronze formed from the sprues, recreating the surface
texture in these areas, and sandblasting remnants of the ceramic
mold from the piece. In the case of a monumental sculpture or
any sculpture cast in more than one piece, the sections are assembled
at this time.
Now the patina, or surface coloring, can be
applied. Years of experience, hours of labor, a variety of chemicals,
and the help of high temperatures hasten what is actually a natural
process, yielding subtle to dramatic coloration.
Vignir Johannsson's "Against the Wind" is now
complete. A certificate is prepared to document the exact size
and weight of the piece, identifying it as the "original" sculpture
it is, with no other in the edition exactly like it. This documentation
acts as a safeguard against fraudulent practices such as surmoulage,
an unauthorized casting taken from a bronze sculpture rather
than from the artist's original.
"Against the Wind" 27.5" H
By Pamela Michaelis, founder of The Collector's Guide and former host of “Gallery News” radio show on KHFM 95.5 , classical radio in Albuquerque.
Photography by Vignir Johannsson taken at Shidoni
NM, during the creation of his piece entitled "Against the
Originally appeared in
The Collector’s Guide to Santa Fe, Taos and Albuquerque - Volume
RESOURCE LISTS UPDATED WHEN VIEWED | ARTICLE CONTENT
October 14, 2009