LOST WAX METHOD
OF BRONZE CASTING

 


HISTORY

In the third millennium BC, somewhere between the Black Sea and the Persian Gulf, an artist created a sculpture in beeswax, covered it in liquid clay and baked it in flames.  In the flames, the wax was lost, replaced by empty space, surrounded by a clay shell.  The artist used copper and tin to make a bronze alloy that the artist poured into the cavity left when the wax melted.  After the molten metal within the clay shell hardened, the sculptor knocked the clay from the metal, and the first bronze was cast.  Today, some 3000 years later and with the help of modern technology, this process is used to create items from the finest jewelry to extremely complex aerospace components.


THE PROCESS

1) ARMATURE The first step requires building an armature which acts as a skeleton for the basic shape and design of the bronze sculpture.
2) CLAY Once the armature is ready, clay is applied over it.  At this point, the details and texture of the bronze sculpture are formed.
3) RUBBER MOLD After the sculpture is completed, a silicone rubber mold is made over the sculpture.
The rubber is so effective at picking up details that fingerprints in the original clay will show up in the mold.  A plaster mold is then applied on top of the rubber mold to help maintain the original shape of the rubber mold once the clay is removed.  A seam is cut in the rubber, and the clay is removed, leaving a negative in the mold.
4) WAX POUR Wax melted to 200°F is poured into the mold.  The mold is rotated and a layer of wax coats the inside of the rubber while the excess wax gets poured out.  This is repeated until there is a 3/16 inch thick wax copy of of the sculpture on the inside of the mold.
5) WAX RETOUCH The wax copy if then removed from the mold and imperfections -such as seams, bubbles, holes- are fixed with hot irons and sculpting tools.
6) SPRUE SYSTEM Wax bars called "sprues" are attached to the wax to create a series of channels.  These channels will eventually be the pathway for the bronze to flow through to reach the different parts of the sculpture.
7) SLURRY The completed wax is then dipped in a ceramic mixture and coated with fine sand.  This is repeated six to ten times depending on the size of the sculpture.
8) WAX REMOVAL The ceramic shell is then drilled at the base until the wax inside is exposed.  The ceramic shell is placed in an autoclave where the wax is steamed out leaving a hollow ceramic shell.
9) CERAMIC FIRING The ceramic shell is then placed in a furnace where it gets fired to 1500°F.
10) BRONZE POUR As the ceramic shell heats up, bronze ingots are melted in a crucible at 2000°F.  The molten bronze is then poured into the ceramic shell.
11) CLEANING After the bronze cools, the remaining ceramic gets taken off with drills and chisels.  The hard to reach places get sand blasted.
12) METAL ASSEMBLY Like piecing together a puzzle, metal workers then weld each piece of a large sculpture together and use grinders to clean up the seams.
13) SAND BLAST Once the piece is completely together, it gets sandblasted to clean the metal and prepare a final finish for the patina.
14) PATINA The sculpture is then heated with a torch and sprayed with chemicals which give each sculpture its unique coloring.
15) FINISH After the patina is applied, the sculpture is waxed and polished and may be place on a marble or wood base. 


CARING FOR YOUR BRONZE

Now that you have purchased your bronze you may think that all that is required of you as the owner is to admire and keep it safe. This is only part of your responsibility. Whether you purchased this piece for your own enjoyment or as an investment to be eventually sold in the open market, it will eventually find itself in the hands of another at some point. It will outlast all of us and continue to give pleasure and conversation to generations to come, so follow these simple guidelines to insure that your bronze sculpture will last several generations.

If your sculpture is placed outdoors where it comes into contact with water, wipe it down occasionally and use a small amount of vinegar to help remove some of the water deposits.  Also be sure to wax your piece at least once a year and more often if you live near the ocean or in high humidity areas - even if your sculpture is placed indoors:
1. Using a soft clean cloth, wipe the surface gently to remove any dust. 
2. Be aware of tiny wires or protrusions that may be delicate and easily broken if caught in the cloth.
3. Use a clean soft paint brush to get into the detail or texture of your piece.
4. If the piece is extremely soiled, dampen a cloth with water and wipe it clean (do not rub!) and then dry it.
5. Using a clean cloth or brush apply a thin coat of Kiwi ® Natural Shoe Wax.
6. NOTE Johnson's ® Paste Wax tends to darken some patinas.
7. Allow the wax to dry (two or three minutes), then buff with a clean cloth
8. Use a soft shoe brush to buff in the textured areas.

  • Never use household cleaners or polished such as Pledge ® or ArmorAll ®.

  • Never store your bronze in packing materials or boxes for long periods of time.

  • Never drape fresh flowers or other organic material over the sculpture.