GAAJ/ Marumo Gemstone Specific Gravity Scale

The specific gravity balance produced by the Gemmological Association of All Japan (GAAJ) represents an important chapter in the modernization of gem‑testing instrumentation. First introduced in the late 1970s, at a time when Japanese gemology was rapidly professionalizing, this dedicated device offered a more stable and purpose‑built alternative to improvised hydrostatic setups commonly used in earlier decades. Its integrated frame, calibrated suspension system, and sensitive scale allowed gemologists to determine a gemstone’s relative density with far greater repeatability—an essential property for distinguishing natural stones, synthetics, and look‑alike materials. This specific gravity unit seems to be more of an experimental SG unit created especially for gemological used.

Compared with earlier hydrostatic rigs—often assembled from laboratory stands, beakers, and generic balances—the GAAJ version introduced a compact, self‑contained architecture that minimized vibration, reduced operator error, and standardized the immersion procedure. The suspended sample holder ensured consistent submersion depth, while the front‑mounted controls and clear scale display improved usability for both students and professionals. This evolution reflected a broader shift in gemology toward instruments designed specifically for gemstone testing rather than adapted from general scientific equipment. Its reliability made it particularly valuable for field gemologists and smaller labs that needed accurate density measurements without the complexity of large analytical systems.

Later generations of specific gravity instruments, including digital hydrostatic balances and electronic density meters, would further streamline the process by automating calculations and reducing manual handling. Yet this GAAJ model remains historically significant as a transitional tool—more refined and standardized than earlier improvised methods, but still rooted in hands‑on measurement and observational skill. 

This is a museum archives and no unit is available for sale at this moment.