Rayner Dialdex Refractometer (c. 1972)

Introduced in 1972, the Rayner Dialdex Refractometer represents a distinctive departure from traditional gem refractometer design. Instead of reading refractive index values directly from a scale within the instrument, the Dialdex employs a unique external adjustment wheel engraved with RI values. Turning this wheel moves a black ribbon-like indicator visible through the eyepiece, allowing the user to align the shadow edge with the ribbon to obtain the correct refractive index easily.

This system offered an intuitive, almost “dial-based” approach to refractometry, reducing reliance on internal scales and providing clearer visibility in varying lighting conditions. The Dialdex’s innovative mechanism made gem identification more accessible to students and field gemologists, while also demonstrating Rayner’s continued experimentation with mechanical solutions to optical measurement.  With the wide graduations between each grids, user can obtain the refractive index down to 0.001.

A product of early 1970s engineering ingenuity, the Dialdex remains a notable example of creative design in gemological instrumentation.

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