Glossary of Pearl Terms Y

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yakkah: Historical Persian quality factor describing natural pearls of secondary quality.

yellow grains: Nineteenth century theory of natural pearl production stating that yellow grains found in some freshwater pearls were from shell-production reserve material. This organic material made its way into the mantle and catalyzed pearl growth.

yoyo: Japanese term for a host mollusk's 45-day convalescence period after implantation of a bead nucleus and donor-mollusk tissue piece.