Calipers
Calipers measure linear dimension. The standard lapidary workshop tool is a 6-inch digital caliper; the Mitutoyo 500-196-30 is a recognized reference instrument with a stated accuracy of ±0.001 inch. Lower-cost alternatives — iGaging, Neiko, Pittsburgh — provide adequate resolution for preform measurement at a meaningfully lower price point but with broader accuracy tolerance.
Dial calipers and vernier calipers remain in service in workshops where digital electronics are undesirable; they require no battery and are mechanically simpler.
Refractometers
A gemmological refractometer measures refractive index in transparent gem material. The standard scale runs from 1.30 to 1.81 RI; the upper bound is set by the available contact-liquid index. The instrument requires a small drop of contact liquid (n ≈ 1.81) to establish optical contact between the gemstone and the hemicylinder.
The hemicylinder is the wear-limited surface on a refractometer. Replacement hemicylinder assemblies are available as service parts from the manufacturer. Birefringence is measured by reading two RI values at perpendicular polarizer orientations; the calcite dichroscope and built-in polarizer support this measurement.
Carat scales
Electronic carat scales report mass to 0.001-carat resolution at capacities up to approximately 100 carats. The standard reference instruments at this resolution are the GemOro and Acculab lines. Calibration is performed against a known mass; calibration weights of 50 ct or 200 ct are typically supplied with the instrument or sold separately.
Loupes and microscopes
10× and 14× hand loupes — Bausch & Lomb Hastings, GIA, Belomo — are the standard tools for naked-eye inclusion assessment. The Hastings triplet design corrects spherical and chromatic aberration to a degree that supports gemmological observation; lower-cost doublet and singlet loupes are suitable for casual inspection but produce edge distortion at the working edge of the field.
Stereo zoom microscopes (Eickhorst, GIA, Leica) provide 10× to 60× magnification with a darkfield stand and overhead illumination. The instruments are used for inclusion identification, treatment detection, and fracture mapping.
Specialized gemmological instruments
The polariscope determines whether material is singly or doubly refractive. The dichroscope identifies pleochroism in doubly refractive material. The thermal-conductivity tester — the Presidium line — distinguishes diamond from common simulants based on thermal response. These instruments support species identification but do not by themselves constitute a complete gemmological workup.