The Bronze Casting Process
On this page I tried to capture the gist of the bronze casting process as
I learned it from William Barnett, an Austin artist who teaches at
The Elisabet Ney Sculpture Conservatory in Austin, Texas. Emphasis is on the bronze casting process itself, so I would recommend a new sculptor take at least one sculpting class first (since only about 3 weeks in 8 are spent creating a sculpture in wax). The Ney
offers classes that teach sculpting in clay (figurative and abstract), plaster, concrete, and stone (limestone and alabaster) as well as offering a life drawing class. Prices are incredibly affordable, the atmosphere is great, and everyone learns so much! In fact, many artists in the bronze casting classes are repeats--it is a very affordable way to create a work in bronze.
First a sculpture is made in wax. We used microcrystalline wax mixed
with paraffin (different ratios depending of hardness desired). The wax
should be soft enough to shape and yet hard enough to stay put and
hold detail. Any mixture will be softer when heated and harder when cold,
so an exact science did not seem necessary. When I made my sculpture
"Sea Turtles I", I discovered the joys of sculpting in wax. The sculpture
was small and required little special handling. I sculpted mostly with
dental tools, which were also very portable. I found myself sculpting any
time I had to wait for any reason. (Since I know how much I hate to wait,
I usually carry something to do with me at all times. This really helps
to "chill me out".)
|Generally, it is best to have some idea of what you want to
create before you start--no matter how vague an image it might be. I often
start out with a very generalized notion of something and, as I develop it,
the piece seems to help me determine how it will end up. The photo at the
right is an image I took of my two turtles and the kelp. I intended to cast
the three parts individually but needed to plan out (before they were
solidified in bronze) how they would work together. Since the weather was
getting warmer (this is Texas!) and I had to be careful
with my sculpture repositioning itself, the photo was to help me recreate my
After the wax sculptures are completed, they are attached to wax funnels.
I forgot to photograph this stage, so bear with my explanation please.
The sculptures are attached to this funnel by "welding" wax sticks (sprues) to both the sculpture and the funnel. The tip of a metal tool is heated up (over a torch). Then a wax stick is joined to the wax funnel by using the hot metal to melt the two pieces together. Sculptures are attached to the opposite ends of these sprues in the same way. There is definitely a trick to doing this well and it does take some practice to make strong welds.
Sculptures are generally placed close to the bottom of the funnel (since the bronze starts to cool the second it hits the funnel). Thicker sprues are joined to the sculpture where the bronze will enter (the bottom), while
thinner sprues (vents) are joined at the top edges of the sculpture and reach to the top plane of the funnel. Sprue placement is very important, since the air that is in the mold before the bronze is poured must escape (otherwise it forms air pockets which the bronze cannot fill). Also, since using this method creates sculptures of solid bronze, our pieces should not be more than about 1-1.5 inches thick.
Our instructor, Bill, then takes the class's wax contraptions to a
foundry. An ceramic shell mold is made around the wax and the wax is
melted out of the mold. This is the scary part because the original
sculpture no longer exists. If the mold is broken or damaged somehow, the
artist must start over from scratch. The molds are returned to Bill and
we are ready for our casting weekend.
||We are now at the home and foundry of artist Bill Barnett. The image on the left is of one student removing a mold from an oven (the big white cylinder in the top center--lifted by another student via cable and pulley). The bronze should not be poured into a cold mold. Bill can be seen in the background (right of center) removing the melted bronze from the furnace. The mold is then set into a big metal pot filled with sand (which safely supports the mold).
|The image on the right is of Bill supporting the crucible filled with liquid bronze while two students tip the container, pouring the hot metal into the mold.|
The hot mold is carefully removed, kept in an upright position, and allowed to cool. (This does not take long--15 minutes?.)
Once the bronze has completely cooled, the investment mold
must be chipped away (most of it cracks fairly easily, but the stuff that
gets stuck in the cracks and crevices is very difficult to remove). The
sprues (now solid bronze) can be cut away with a hack saw or other tool and
remelted later (although only once or the quality of the bronze deteriorates). The final cleaning and shaping of the sculpture is done with a Dremel tool and/or a sandblaster. A
patina is added to the sculpture as desired.
A rubber mold of each turtle was made before the turtles were joined to the kelp. (I planned to do a series on sea turtles.) The next step was to
carve the limestone base and do the finishing work. The
finished piece was first shown (and won 1st place in the bronze category as
well as the People's Choice award) at the 11th Annual Student/Faculty Exhibit of the Elisabet Ney Sculpture Conservatory August 15-28, 1997.
(Thank goodness for shows--they are real motivators!)
Continue the demonstration.
See the finished piece, Sea Turtles I.
See the finished piece, Flying Sea Turtles.
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