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Lost Wax Casting Technique Steps
2016-02-24

This is Lost Wax Casting process steps

Step 1

The first step begins with creating an original sculpture. I typically create the original clay, though other materials can be used as well.

Step 2

The clay is prepared for molding by applying a silicone based liquid spray that acts as a release agent. This agent keeps the mold from sticking to the pattern when removing. Next, a urethane or silicone rubber mold is applied to the pattern one coat at a time. The first two coats are very thin to capture details of the pattern and to ensure that no bubbles or air pockets form on the surface. Shims of plastic that have spherical buttons are inserted along the seam line after the first two coats of the mold. The buttons ensure that the mold fits back together correctly after it has been taken apart.

After the pattern is completely incased in rubber, a shell is constructed called the ‘mother mold’, which is made from moulding plaster reinforced with hemp fiber. The mother mold will keep the rubber, which is malleable, in the correct shape once the pattern is removed.

Step 3

Chasing the Wax: The wax is pulled from the mold and hand chased (re-detailed) by a skilled artisan. Although the artist reproduces the original artwork, each piece may slightly differ from the next.

Step 4

The wax casting is removed from the mold, and one of the Sculpture Center Foundry's artisans hand- finishes the wax pattern to original perfection. Each wax casting is treated as if it were an original work of art.

Step 5

Next, the wax is covered in a ceramic shell mold, called 'investing'. It is dipped into a liquid ceramic slip made from colloidal silica and silica flour. This slip, called 'slurry', sticks to the wax while the remainder drains back into the mixing tank. Silica sand, called 'stucco', is then poured over the surface sticking to the wet slurry. Fine stucco is used for the first few coats ensuring that the detail is captured. Coarser stucco is applied to the outer coats to add structure and strength to the mold. Each coat dries for several hours before the next one is applied. This process is repeated until the desired thickness of 1/4" - 1/2" is achieved and usually requires 6-8 coats for smaller molds and as many as 20 coats for large molds.

Step 6

Spruing – Wax cylinders are attached to strategic points around the wax copy creating pathways for the molten metal or alloy to flow into the mold and for air to escape.

The piece, now coated in ceramic shell, is fired in a kiln. This bakes the shell and eliminates the wax, leaving a cavity in its place. (Thus, the term, "LOST WAX")

Step 7

After the metal has cooled, the ceramic mold material is gently chipped off using a hammer and chisel. The remaining mold material left in the crevices is sand-blasted. Next the sprues, which are cast in bronze along with the pattern, are cut off using an angle grinder and metal cutting disc. The stubs left behind are sanded off using various grinding and sanding tools.

The cast parts are then checked to make sure they fit together properly. Necessary adjustments are made and then the parts are welded together. The welds are chased, also using various grinding and sanding tools. Surface textures are replicated with various tools so seam lines and sprue attachments are no longer visible.

Step 8

After cooling for several hours, the ceramic shell is carefully broken away, revealing the bronze sculpture within.

Any fragments of the ceramic shell are removed by sandblasting. The sculpture is also carefully inspected at this point.

Step 9

Fine sand particles are blasted under air pressure to remove the last traces of ceramic shell that adheres to the bronze.

Step 10

An artisan cuts away the sprues and gates. After this, the pieces of the sculpture are welded together by skilled craftsman.

Testing – Once the ceramic shell has cooled sufficiently water is run through it to ensure there are no leaks or cracks. Any imperfections in the shell can be fixed after which it is reheated to harden any patches.

Step 11

By grinding, chasing, sanding and polishing, all areas are blended back to make the bronze look exactly like the artist's original sculpture.

Step 12

The chased bronze is now treated with chemicals and heat to give it the chosen color according to the artist's specifications. The patina is sealed under a wax coating and becomes part of the sculpture.