Skilled craftsmen will take the finished sculpture and make a determination on how the sculpture will be sectioned or "laid up" for mould making. Complex moulds will require the original artwork to be cut into smaller manageable pieces. This is, by far, the most critical step of the procedure. The detail of the original must be captured and transferred in the mould, if not, they will be difficult to replace in any other step.
The sculpture is first sealed and then a release agent is applied to allow for easy removal of the rubber mould.
After the original sculpture has been prepared, the mould Maker will apply the first coat of rubber. Once the rubber has set, additional coats must be applied and "keys" will be placed in the rubber to ensure proper positioning of the mould.
When the rubber is thoroughly set, a back-up shell or "Mother Mould" is applied to support the rubber for the wax pouring process. Previously, plaster was used for this process. Today, the most widely used material is fiberglass due to it's strength, durability, and, weighs much less than plaster. A release agent is applied on one half of the rubber mould then the fiberglass is laid down on the rubber, followed by the resin and allowed to dry. Depending on the size of the mould and the strength needed, several coats may need to be applied. Then the mould and mother mould are flipped over and the process is repeated on the other half. The back-up shell is removed and the rubber gently pulled back so the original sculpture can be removed. The rubber is then cleaned of any remaining particles from the original. It is now ready to receive the wax.
The completed mould, having already been prepped, is now ready for the wax. The mould is separated and the first coat of wax is painted into the mould to capture all the fine details of the artist’s sculpture. The mould is put together and more wax is poured in. It is then rotated until an even, thin coating is achieved. The excess wax is poured out. After the wax has completely cooled, the "mother mould" followed by the rubber mold is removed. Now the wax casting is revealed.
Seam lines are removed and the wax pieces are fitted for alignment. Then the register marks are put in, followed by the final wax inspection. Then cut up for bronze casting
Wax rods are attached to the sculpture. These rods are called sprues. A large cup is attached at one end, this cup will receive the molten bronze when poured. The placement of the sprues system allows molten bronze to flow through these areas allowing gases to escape through smaller bars called vents.
We are now making a secondary mould. We now dip the wax in a liquid ceramic solution. This material is called "slurry" and a very fine sillica sand is applied. Each coating is completely dried prior to the next. The number of coats applied to a piece is determined by the size and weight of the piece. The heavier the piece the thicker the shell must be to support the metal. The slurry coats the inside and outside of the wax allowing the sculpture to be hollow. The chemical make-up of the slurry is monitored constantly to ensure it's strength. The humidity and temperature of the slurry room is controlled to allow for optimum dryness and hardness of the shells.
The ceramic shell is removed from the coating room and placed in a burn-out oven cup side down. A burn-out oven is simply a large flame in a controlled space that allows the shells to de-wax. Once the shells are de-waxed, they are cooled and inspected for cracking. Once again they are heated up to 1400 degrees and placed in the pouring pit. Bronze ingots are heated from 1900 to 2100 degrees. The temperature that bronze is poured is determined by each individual casting. The molten bronze is then poured into the hollow shells and allowed to cool and solidify.
The shell material is now removed inside and out, and the unfinished bronze casting is revealed. It is then water blasted to remove any remaining shell material from the intricate details of the casting. All the sprues and the cup are cut off.
If the original was sectioned into multiple pieces, it would now be carefully fitted and reassembled. A visual inspection is done to check for any casting inclusions. If there are any surface defects, these would also be repaired at this time. All sections of the casting are welded together with great care and attention to alignment.
The sculpture is worked to remove any sign of welding or casting defect and to prepare the bronze for the patina (coloring process).
The patina is the finished colour. Depending on the artist's preference, we may use a variety of different chemicals which react to the metal to achieve a certain look. Colours like, Antique Brown (ferric nitrate) , Verde Green (copper nitrate), white (bismuth nitrate). After the patina is applied, and depending on whether the artwork is inside or outside, the sculpture is sealed with a wax coat and/or lacquer to protect the finish.