The mold making process begins with the creation of a master-mold composed of two separate parts, the rubber mold and the mother mold. The master-mold will be used to create a duplicate hollow wax positive.
Step 7- Preparing to Make a Mold
After taking reference photos of the finished sculpted clay piece Ms. Mongeon will often cut apart the sculpture. It is cut in areas that will best facilitate the mold making and casting process. The photos of the finished clay sculpture will be used later in the process of assembling the metal sculpture.
Any part of the armature that sticks out of the sculpture, like metal supports, are cut away at this point. This is where careful planning in the armature stage is critical, because the armature left inside the sculpture has to be able to support the weight of the sculpture. Kipper's clay sculpture weighed about 300 lbs.
Step 8-Creating Mold Seams
There are several ways of making seams for molds. This process consists of using sharp metal shims into the clay sculpture in a specific pattern. For example, the shims will separate the front mold from the back mold, creating a seam between them. Like anything else, placing the shims must be carefully planned. These shims are what cause the molds to fit together like pieces of a puzzle. The sculpture is also sprayed to seal the clay and to help the rubber release from the sculpture.
Step 9- Applying the Rubber Mold
Rubber is painted on the sculpture very carefully, a layer at a time. It is important not to get any air bubbles in the rubber and to give a thorough covering to retain detail. Many layers of rubber will be needed to create a sturdy thick mold that holds detail.
The rubber mold is composed of two part liquid mixture, that are kept separate until just seconds before application onto the clay sculpture. Once combined the mixture cures within a minute to a hardened rubber. The rubber is mixed and applied six ounces at a time.
Step 10- Applying the Mother Mold
After several coats of rubber are applied and cured Ms. Mongeon makes a plaster mother mold. Without the mother mold the rubber mold would not keep its shape when pouring wax. The mother mold is made of plaster and hemp.
Once the molds are completed they are taken apart and cleaned. The original sculpture is usually destroyed in the mold making process and is discarded. However, any large pieces of the original clay sculpture that survive the mold process are stored as reference along with the photos of the sculpture before it was cut apart. This reference material is valuable when assembling the metal sculpture.
Continue to the Wax Process.
(More about the mold making process can be found on the artist's forum and in the online Newsboy Journal.)