How to Make a Mold for a Bronze Casting

Draw the design concept from different angles.

Use the concept drawings to sculpt a wax model. Keep the wax under the heat lamp to maintain workability. For a complex sculpture, divide the model into parts, carve each separately then join them together by heating the wax at the joining points.

Attach sprues to the wax model. Sprues are made of wax and are a part of the process of forming channels for filling the mold with bronze and allowing gas to escape.

Put on the waterproof safety gloves and safety goggles. Pour the investment casting silica slurry into a container large enough to set the entire wax model into. Pour the investment casting fine grain silica into a container large enough to set the entire wax model into.

Dip the wax model into the fine silica slurry making sure all surfaces are coated. Hold the model over the silica slurry container and allow excess to drain off. Move the model to the fine grain silica container and set it down into the silica. Coat the model with the fine grain silica. Place the model on a rack to dry. Repeat this process seven to eight times until you have a 1/4-inch-thick shell. Make sure the ends of the sprues are not coated in this process, wiping off any slurry or silica that get on them.

Place the model in the furnace, positioning it so that the melted wax will drain out of it. The furnace's temperature and the time the model is left in the furnace depends on how big the model is. Refer to "Lost-Wax Casting" by Fred R. Sias in the references for a chart on times and temperatures.

Remove the model from the furnace. Place it into the tub of sand to hold it.

Melt the bronze in a crucible. The temperature depends upon the alloy composition. Bronze of 10 percent tin and 90 percent copper has a melting temperature of 1560 to 1832 degrees Fahrenheit.

Use the heat safety gloves, goggles, protective clothing and the tongs to pour the molten bronze into the model in the sand.

Allow the metal to cool. Remove the coating from the bronze. Saw off the sprues.

Polish the bronze piece.