Metalworking in Bronze Age China: The Lost-Wax Process By Peng Pe ...

wax model of the horse. A system of gating or venting, composed of wax rods for the pouring of metal and venting of gases, is attached to the model.⁷ Subsequently, an investment mold is made by packing clay all around the wax model, presumably in multiple layers.⁸ The investment mold is then baked, during which process anything made of wax (i.e., the model and its sprues) melts away from the mold. The now-hollow mold is inverted to receive the molten metal, which lodges in the space previously occupied by the wax, in this case the horse figurine model and its gate system. After the poured metal solidifies, the investment mold is broken open, the gate system removed, and the bronze horse revealed, cleaned, and perhaps further refined.⁹ Because metal shrinks during solidification, cracks can easily emerge on thick, solid castings. To prevent shrinkage and to conserve metal, one or more clay cores held in position by metal chaplets can be added within the casting to create a hollow form.¹⁰

Compared with section-mold casting, the primary benefit of the direct lost-wax process lies in the stage of the mold’s construction.¹¹ Because mold sections do not have to be removed from the model, the lost-wax process is theoretically capable of casting objects of any shape, even those with formidably deep undercuts.¹² Meanwhile, behind the “theoretical elegance and simplicity” of the lost-wax process is “much skill in its application.”¹³ As Bagley pointed out, the lost-wax caster is not completely free from shape constraints: to avoid trapping air when the mold is filled with metal, the gate system becomes correspondingly more complex the more intricate the shape to be cast.¹⁴ Compared with section-mold casting, the lost-wax procedure, moreover, has some apparent disadvantages. For example, founders are unable to inspect the interior of the enclosed investment mold to detect potential defects before casting.¹⁵ More importantly, the wax model, as the artist’s original, is “lost” so a new model must be made if another product is wanted, or if an accident happens before or during casting.¹⁶