London Dichroscope (c. 1996)

Introduced in 1996, the London Dichroscope represents a pivotal shift in 20th-century gemological instrumentation toward practical portability and manufacturing efficiency. Prior to its release, dichroscopes depended almost exclusively on Iceland spar (optical-grade calcite) crystals. While calcite provides superior light throughput for identifying subtle color shifts, its scarcity, weight, and high cost restricted widespread accessibility.

The London Dichroscope replaced the traditional calcite prism with two adjacent linear polarizing films oriented at right angles (90°). Positioned inside a matte-black anodized housing—styled after a standard jeweler's loupe—the design shields the internal films from dust, abrasion, and ambient reflections. When held close to the eye toward a light source, the instrument presents twin viewing windows that isolate orthogonal directions of polarized light side-by-side, eliminating the need to manually rotate the optical body during inspection.

As documented in the Journal of Gemmology (1997), the device was developed jointly by Gem-A’s Education section and Gem Instruments Ltd. Its low weight, impact resistance, and economic production made it a global standard for field collecting, trade shows, and classroom instruction.