News — Gem Refractometer

Discover how the RGM-100 Gem Refractometer measures gemstone refractive index. Follow step-by-step instructions for preparing a stone, applying contact fluid, reading the RI scale, examining double refraction, and maintaining your instrument.

This in-depth guide compares 1.800 nD and 1.81 nD gem refractive index fluids, explaining how each is used with gem refractometers like the GIA Duplex II and NI Supply RGM-700 for accurate gemstone identification. It highlights that while the 1.81 fluid offers slightly higher measurement capability, the more affordable 1.800 fluid effectively covers nearly all gemstones, making it the best value for most users. The article also explores the extremely narrow 1.800–1.810 RI range, listing the few gemstones affected and showing why the difference is minimal in real-world testing. Ultimately, it recommends a dual-fluid strategy for professionals while emphasizing the cost-efficiency and practicality of the 1.800 RI fluid for everyday gemology work.