Figure 1. Sponge coral, because of its porous nature, is often impregnated with plastic to strengthen it. Note the continuous pattern of plastic-filled cavities in this 54.88 ct piece. Photo by C.D. Mengason.

The GIA Laboratory in Carlsbad recently began to receive multiple beads of various sizes and shapes for identification. They initially appeared to be a plastic-impregnated variety of coral often referred to as "sponge coral" because of the numerous natural voids typical of this material. It is a common practice to fill these voids with plastic to strengthen the coral and make it more suitable for jewelry use (figure 1).

Close inspection of these beads, however, showed a lack of continuity in the pattern of round- to oval-shaped cavities that are characteristic of sponge coral. There were large areas that had no structure at all and were filled with numerous tiny irregular pieces of some other material (figure 2). It became clear that these samples were in fact a composite of fragments of sponge coral held together with an orange plastic that had been mixed with a ground-up material, probably coral or shell.

Figure 3. After it was soaked in methylene chloride to remove the plastic, the bead in figure 2 disintegrated into fragments. Photo by C.D. Mengason.

To confirm this identification, we soaked a single bead in a bath of methylene chloride for approximately 48 hours. This caused the plastic component to dissolve and the bead to disintegrate into its composite pieces (figure 3).

This is the first time we have encountered such an assemblage with coral, although a similar intent was evident in recent samples of ruby fragments held together with a high-lead-content glass. Therefore, we described the new material on the laboratory report in the same manner, calling it a "coral/plastic composite."

Kimberly Rockwell
GIA Laboratory
Carlsbad, California