Osiris

This Osiris figure is said here to be made of cupreous metal, a convenient term used for copper and copper alloys until their composition are confirmed by instrumental analysis. It is likely bronze, a mixture of copper and tin. With the exception of the head and hood of the cobra on the god’s forehead and his false beard (both no longer in place), the statue was made in a single piece using a direct lost-wax casting process.

The direct casting method cannot be used to produce replicas; the investment (mold) is made directly from a wax model and each cast is unique. When using the indirect method, the artist carves or models an intermodel of a permanent material, such as wood or plaster, that may be used to create a series of identical wax models and produce multiple copies. Both the direct and indirect techniques can be used to produce either solid or hollow casts.

To produce a solid cast object using the direct method, the ancient Egyptian artist made a wax model identical in shape to the intended work. Surface details might be scored or punched into the wax surface. The model was encased in layers of investment, that is, a moistened mixture of clay, sand, and some form of organic temper—chopped straw or hay, for example—that forms a strong, hard outer shell when heated. As the investment was fired, the wax melted out (and hence was "lost"), and molten metal was poured in to replace it. When sufficiently cool to handle, the investment was broken away to reveal the cast, which was ground and polished to remove traces of the casting apparatus and surface flaws, and chased and/or punched, or engraved to add or enhance details.

In this case, the cast is hollow, so the artist used a similar investment mixture to model a core that is slightly smaller than the proposed work but more or less conformal to the desired shape. After the core had been fired, it was clad with wax sheets. Some details are usually modeled in solid wax onto the wax sheets. The model is invested, secured in the investment with core supports, and casting proceeds as above. Ancient Egyptian casting cores are usually black due the reduction of the organic matter during firing. Unlike other ancient and modern metal founders, Egyptian artisans generally did not remove the casting cores from their hollow creations unless they were sarcophagi, intended to contain animal mummies, or some kind of vessel. But cores tend to be granular and easily eroded and thus generally disintegrate if exposed to the elements. What is special about this statue is that we can see the original contours of the casting core, which was fired at a high enough temperature to have survived intact even though the walls themselves were lost.

X-ray radiography is a useful tool for studying casting technology—simply stated thicker masses of a given material appear white, thinner masses appear gray or black. Atomic weight also plays a role, metals are "heavier" than the silica and alumina that make up sand and clay and so metal walls appear whiter than the internal core, even though it is solid. Comparing frontal and profile radiographs of the statue (figures 1 & 2), one may observe the following: the regalia (a scepter in the left hand and a fly whisk in the right) on the god’s chest, the tail of the cobra of his uraeus, his ears, and the thumbs and knuckles of his clenched fists were all modeled in solid wax; the neck is solid, which means there were two cores, one for the head and crown and one for the body, joined with wax; the walls of the mummiform body are more or less the same thickness, in contrast to the face and the chest and upper back that were built up with additional layers of wax. The use of separate cores joined at the neck is not uncommon for human figures of this size, and was likely done to avoid breakage of the friable core at this vulnerable location during the preparation of the model and investment.

The square black feature visible on the forehead in the frontal view radiograph is an opening in the metal wall that accommodated a tang for attaching the separately cast uraeus; the radiopaque (white) square in the center is the broken off tang end still embedded in the core. A more formless pale gray patch on the chin is more clearly recognizable in the profile view as a similar opening for the beard. Other gray patches scattered across the body are losses, often extended by cracks, most of which can be seen in on the surface. Also visible in the frontal radiographs, several here indicated by circles (figure 3), are the locations of the iron supports that held the core in place within the investment during the time when the wax had been melted out and the metal not yet poured in. These supports tend to rust in situ and generally are not visible on the surface, even to the trained eye.

Deborah Schorsch 2020

Department of Objects Conservation

Donated to the Museum by Elisha Dyer, 1941.

Hill, Marsha and Deborah Schorsch 2016. "Ptah's Profile." In Another Mouthful of Dust. Egyptological Studies in Honour of Geoffrey Thorndike Martin, TIP/25 pp. 274-287, figs. 15-16.