Erb & Gray “Jewel" Refractometer (c. 1960s)

The Erb & Gray “Jewel” Refractometer emerged during the 1960s, a period when small optical workshops were refining tools for jewelers who needed dependable diagnostic instruments. The company was founded by Max Erb, a skilled instrument maker known for producing precision tools for the jewelry and watchmaking trades. Partnering with Gray, the firm combined Erb’s craftsmanship with practical engineering, creating compact optical devices that bridged the gap between laboratory instruments and everyday bench tools.

Building on Max Erb’s experience in fabricating high-quality loupe systems, measuring devices, and optical components learnt from the microscope systems, the Jewel refractometer incorporated a precision-ground prism and a straightforward illumination path, prioritizing durability and clarity. One of its defining features was the vertically movable eyepiece, which allowed users to slide along the refractive-index scale to directly observe the critical-angle shadow. This approach simplified operation, reduced internal optical complexity, and made accurate RI readings more accessible to jewelers who previously relied on larger, more specialized equipment.

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