Casting Page

In this step, a skilled artist carves what is referred to as a "model", usually in a hard, special type of wax.

This piece, although called a "model", is in reality a precisely detailed, 3-dimensional, actual-size wax prototype of what will become the final metal product.

The final product may ultimately be cast in gold, silver, bronze or other metal.

2. Invest Wax Model

In this step, a worker takes the wax model produced in Step 1, places it in a metal container and completely covers or "invests" the model with a liquid plaster (called "investment").

Before investing, the worker attaches a small wax rod (called a "sprue") to the wax model in order to connect the model through the plaster to the outside.

3. Burn-Out Investment

Once the plaster investment (prepared in Step 2.) has set, a worker places the investment into a special oven for several hours at around 1,300º F.

At this temperature the wax model completely melts and the melted wax runs out of the plaster investment through the channel provided by the melting wax sprue. No wax residue remains within the investment.

This step leaves a hollow space inside the plaster investment that, in negative, exactly reflects the shape of the original wax model.

It is this step, in which the wax is melted out of the investment, that gives the name of "Lost Wax" to the process.

4. Cast Metal

In this step, a worker pours (or injects via vacuum or centrifugal force) molten metal through the sprue channel into the cavity of the plaster investment created in Step 3.

5. Dissolve Investment

Once the molten metal cools, a worker uses immersion and water spray to dissolve the plaster investment surrounding the newly cast piece.

6. Clean/Finish Casting

When the rough casting has been freed from the investment plaster, an artist cleans, files, finishes and polishes the cast metal piece to an even finer finish than the original wax model.

If only one piece is to be made, the process is now complete.

However, a manufacturer usually intends to make more than a single piece. In this case, the newly cast and highly finished metal piece becomes the "Master Model" and basis for the next step and all future production.

7. Make Rubber Mold

This step is functionally very similar to Step 2, above, where a single-use plaster mold was made around an original wax model.

Here, however, instead of plaster being poured around a wax model, a special silicone rubber is molded under heat and pressure around the metal "Master Model" (made in Step 6.) to form a multi-part, reusable rubber mold.

The Master Model is set then aside and carefully preserved for possible future use.

8. Inject Wax Patterns

Using the Rubber Mold made in Step 7, a worker injects molten wax to form multiple wax replicas of the piece to be cast in metal. These replicas are known as "Patterns".

9. Build Wax "Sprue Tree"

A skilled worker now assembles from one to several dozen of the wax patterns (produced in Step 8.) onto a central wax core or sprue to form a "Sprue Tree".

The number of patterns that make up a single sprue tree depends on the size of the pattern, the number of pieces desired, and the type of casting equipment being used.

10. Invest the "Sprue Tree"

This step is identical to Step 2, above, except that instead of pouring investment plaster over a single, hand-crafted wax model, the investment is poured around the wax "Sprue Tree" prepared in Step 9.

11. Burn-Out Investment

Once the plaster investment (prepared in Step 10.) has set, a worker places the investment into a special oven for several hours at around 1,300º F.

At this temperature the wax patterns melt and the melted wax runs out of the plaster investment through the channels provided by the melting wax sprue tree. No wax residue remains within the investment.

This step leaves hollow spaces inside the plaster investment that, in negative, exactly reflect the shapes of the wax patterns, and hence the metal "Master Model".

Again, it is this step, in which the wax is melted out of the investment, that gives the name of "Lost Wax" to the process.

This is essentially the same as Step 3, above.

12. Cast Metal

In this step, a worker pours (or injects via vacuum or centrifugal force) molten metal through the sprue channels into the cavities of the plaster investment created in Step 11

This is essentially the same as Step 4., above.

13. Dissolve Investment

When the molten metal has cooled, a worker uses immersion and water spray to dissolve the plaster investment surrounding the newly cast pieces.

This is essentially the same as Step 5., above.

14. Clean/Finish Castings

When the rough castings have been freed from the investment plaster, an artist cleans, files, finishes and polishes the cast metal pieces to the desired specifications and appearance of the finished item.

The manufacturing process for this lot is now complete.

Depending on the design of the final product, however, additional steps of assembly, soldering, stone setting, etc. may be required.

Future lots of the same design will repeat Steps 8 through 14.