A Guide to the Lost Wax Process
With illustrations and text by Lee
Ann Gunn, based on her full page feature in The Boston Herald on
January 7, 2000.
This is the story of how Nancy Schön goes
about creating a cast bronze sculpture. The example being used is
her well known Make Way for Ducklings sculpture in the Boston Public
The article by Lee Ann Gunn was written after Jack,
one of the ducklings was removed by a scoundrel, and Nancy had to
create a new Jack.
The Children's Book
Nancy used the book "Make Way
for Ducklings" and original sketches that author Robert McCloskey
donated to the Boston Public Library to develop her favorite poses
for the 8 ducklings and Mrs. Mallard.
From her sketches and reference materials,
Schön first make a maquette, or a small 2 foot by 4 inch scale
model, of the sculpture in wax. When she makes a presentation she
shows the maquette. It allows others to visualize what her finished
sculpture will look like.
Nancy next starts on the actual size
sculpture. She makes it in clay first. She uses plumbing pipes and
aluminum wire to create an armature, which will serve as the bone
She attaches styrofoam pieces with wire mesh
around it to build up the body.
Once she has a rough shape she covers
it with Plasticene, a non-hardening clay, and continues adding clay
to form the duck.
From this point on, Nancy works with
a foundry in Everett, the New England Sculpture Service.
A polyurethane rubber mold
is made from the clay form. Depending on size or complexity of the
piece, the rubber mold may have to be in several pieces; the mold
for Jack was in halves.
Foundry owner Jim Montgomery
says they paint the first rubber coat on, then use a spatula for
Then they cover the rubber
with with plaster of Paris, making a two-part 'mother mold' which
holds the rubber in place.
Montgomery or one of his coworkers pours
hot wax into the rubber mold to make a hollow wax cast. After the
wax cools and is removed from the rubber, Schön uses small, sharp
tools to correct flaws in the wax model. "This is the most important
part. If we want a bronze, you have to make a wax," says Nancy.
Next, a ceramic shell is made. The
ceramic shell is important because it carries the shape and texture
of the wax to the bronze metal that will be poured into it.
To get the ceramic mold, the wax figure is dipped
into a tank of a water-based ceramic mixture. A funnel is attached
to the figure before it is dipped to allow the bronze to be poured
During the dipping, ceramic liquid goes inside
and outside Jack. Ceramic liquid clings to both sides of the wax,
so the two layers sandwich the wax.
The wax Jack is dipped 11 times in the ceramic
liquid and hangs on a clothesline to dry between each dipping.
After the ceramic is cold, the wax figure in it's
ceramic shell is placed in an oven to melt out the wax. Then the
empty ceramic molds are fired in a kiln for about four hours.
While the ceramic figures are still
glowing orange from the heat of the kiln, Montgomery and his team
pour the molten bronze from a hoisted crucible into the ceramic
molds. Where the wax was, the bronze fills in.
As soon as the bronze has cooled inside the ceramic,
the ceramic shell can be chipped off. The finished bronze sculpture
is about 1/4 inch thick.
Once in bronze, the foundry can make small changes
to, or chase, the surface. The foundry uses chasing tools of different
sizes and shapes and air grinders to chip off small pieces, close
small holes and smooth over seams on the finished bronze sculpture.
The final coloring or patina of a bronze
sculpture is applied using a combination of chemicals and heat.
Schön comments, "We have to do in an
hour what it takes Mother Nature 10 years to do".
In order to install a sculpture, stainless steel
rods are inserted in the bottom of the sculpture protruding a sufficient
number of inches to be buried in cement footings. These footings
must be below the frost line in order to keep the sculpture in place
with the change of temperature.