Custom Bronze Sculpture 101
Just like any trade or profession, the world of bronze figurative sculpture is full of terms and concepts that are new to most of our clients. Below are a few words, phrases and concepts that will help to get you up to speed so that you can speak the language.
The word “maquette” (pronounced “mock-ette” in the US), is one of those strange vestiges of the historical past of figurative sculpture. It is simply the French word for “scale model”. Typically on a life-sized or larger bronze commission, a sculptor will create a maquette so that you the client will know exactly what you can expect to see in the larger, finished monument. This maquette shouldn’t be any less than 1/3rd the scale of the final monument. For example, a life size sculpture should have a 24 inch tall maquette. Any sculptor with sufficient training will include the cost of creating the maquette in the cost of your monument. This is both for their protection and yours. It is much easier to act on a suggestion at 1/3rd scale than it is at full size!
An armature is the rigid structure inside a maquette or a full sized sculpture. On a simple standing figure, the armature often looks much like a primitive skeleton. The structure gets more complicated on larger or more complex statues. When a maquette is created the armature is usually flexible aluminum wire, and on a large sculpture the armature should be welded steel to support the weight of the clay.
Life-and-a-half, or life-and-a-quarter
These two phrases simply refer to the scale of the final statue. Typically, for an outdoor monument, the smallest scale that is appropriate is life and a quarter, or 125% of life-size. The reason for this is that it seems we humans have an inflated sense of ourselves! A life sized statue placed under the big blue sky seems small, and that is the last thing you want if you are honoring someone. Even on a small plinth a life-sized statue seems strangely diminutive. Life and a half (or 150%) and larger scales are typically referred to as “heroic scale”. At this scale an adult male would be 9 feet tall. This is the right scale for a centrally located sculpture that is to be the focal point of a park or common area. You would be amazed how much smaller a 12 foot tall statue looks when it is out under the vast sky. A well trained sculptor can easily tell you what scale will achieve the feeling that you desire.
Pointing up is the phrase that refers to the actual process of transferring measurements from the maquette to the full size sculpture. This phrase is most often used in stone carving, as many sculptors today skip the maquette process entirely. We firmly believe that a well thought-out maquette makes for a better monumental sculpture, and always include it in our pricing. Pointing up can be done in many ways. Our preferred method is using a 3-D pantograph.
The best method for pointing up is a 3-D pantograph. This is a manual device that uses geometric principles to transfer points from maquette to full size model. A pantograph is one of those beautifully simple machines that can only have been designed hundreds of years ago. In fact, many of Auguste Rodin’s large scale sculptures were pointed up, or “enlarged” using a similar machine. We operate 2 pantographs in our studio. The largest is capable of enlarging up to a 12 foot tall figure in one piece. To see a short video of one of our pantographs in action, here is a timelapse video of the partial creation of a 16 foot tall monument that we created. Larger sculptures are either pointed up in 2 pieces, or laser scanned… what is laser scanning you ask?
Laser scanning is a new technology that began to make its way into the fine art bronze industry in the early 1990’s. It is the process of using a laser to take thousands and thousands of measurements of of the surface of a maquette and then create a 3D image in a computer.
That image, or file, can then be enlarged to almost infinite size. Once the final size is decided on, the file is sent to a Computer Numeric Controlled Router, or a CNC machine. It is then cut out of large blocks of urethane foam. The number of sections depends on the size of the monument.
But, remember, just like blowing up an iphone photo, at some point the quality of the large version will start to suffer. The scale of the maquette that is being scanned should still be large enough that the final monument will be a success. It is silly to enlarge a 12 inch sculpture directly to a 12 foot tall sculpture. They are, and have to be, distinctly separate pieces of art. What works at 12 inches rarely works at 12 feet. The other limitation of laser scanning is that it creates the final sculpture from the outside in. The router cuts the foam out to the finished surface, but the cutting bits that the router uses aren’t small enough to exactly replicate the maquette, so there is lots of finishing that needs to be done. Additionally the carved foam is not an aesthetically pleasing surface, so many times a thin layer of clay is sprayed on the foam so that the sculptor can give it that “clay sculpture look” A sculptor must be very careful that this “shortcut” process is used effectively, and does not negatively affect that final monument.
Every bronze figurative monument begins with a master, usually clay. This is the work that the sculptor creates. Once it is finished, in order for the bronze casting process to begin, a multi-piece rubber mold must be made.
This is a very expensive and technically demanding process, and the quality of the mold directly affects the quality of the finished bronze. The mold maker will brush on multiple coats of silicone or polyurethane rubber (the mold maker’s preference determines which). After the rubber is between ¼ and ½ inches thick, a rigid mother mold is made on top of the rubber.
A mother mold is a rigid shell that exactly follows the contours of the rubber mold. The rubber is there to capture the fine detail of the sculpture and to follow curves and contours, but it has no shape. If you drop it on the floor it will lay there like a wet towel. That is why we need a mother mold. A mother mold can be made of any rigid, durable material, and each has their drawbacks and pluses. Some are expensive, some are cheap; some are toxic, some aren’t; some are easy to use, some are very challenging. The preference of the mold maker will hold sway here, there is no difference for the client, provided that the mold maker is skilled with whatever material they have chosen.
Lost wax or Circe perdu
Lost wax is the method of bronze casting most commonly used for figurative sculpture. (Circe perdue is the french phrase) In this method, molten wax is poured into the mold, producing a hollow wax copy of the sculpture. For a life size statue there will be as many as 10 mold sections and a corresponding wax casting for each mold section that comprise the entire figure. After the wax is created, the foundry adds wax channels called gates and sprues that will allow the wax to escape, and then allow for the molten metal to get in. They also add a big funnel for the molten metal to be poured into, called a pouring cup. Next the wax is dipped in a material called ceramic shell. This is a ceramic liquid and a silica sand that, over the course of multiple layers, covers the wax with a thick, fireproof and heatproof shell. After this is completed and entirely dry, it’s time for casting. On the casting day, the ceramic shell pieces are placed in an oven that quickly gets to the liquid temperature of the wax, melting the wax out and leaving behind an empty, hollow form. Next, the glowing hot shells are moved from the oven to a sand pit, placed with pouring cup facing up. Then, when the bronze is molten, it is picked up in a big pot called a crucible, and molten metal is poured into the ceramic shells. These pieces are allowed to cool, then they are sandblasted to remove all of the ceramic shell. After this the sprues and gates are cut off with grinders, and the foundry sets about to welding all of the pieces back together to create a big statue.
Chasing is the process of taking all of the pieces and reassembling them into a finished sculpture. The pieces are welded together, then the welds are sanded down and the foundry workers use hand tools and air tools to texture the weld seams to match the texture of the clay. A good indication of a subpar sculpture is being able to pick out the weld seams. If you can see where the pieces were welded back together, someone didn’t know what they were doing, and they certainly weren’t going to guarantee that statue for 100 years!
Silicone bronze is the family of bronze alloys that are the gold standard for fine art bronze foundries. The properties of silicon bronze make it both an ideal metal to work with when creating bronze sculptures, as well as the most long lasting and durable metal for any public artwork that will live its entire life out under the sun, wind and rain.
The standard first protective layer for an outdoor bronze monument is a synthetic lacquer. There are many different lacquers and most are very similar in effect which is a long-term, durable finish that protects the bronze from the effects of the weather. But… everything is relative, and long-term only really means long-term if you do annual maintenance on your sculpture.
Paste wax is the second protective layer on your bronze statue. This is a hard wax like Johnson’s paste wax (yellow can) or Trewax brand. Wax should be applied at least once every year to protect the lacquer and bronze finish and to rejuvenate the appearance of the monument.
Now you are an expert!