Rayner “Blende” Refractometer (c. 1939)

This 1939 Rayner refractometer introduced a significant departure from traditional gem-testing design. Instead of the usual hemispherical or hemicylinder prism, it employed a truncated 60° prism—a form developed through experiments conducted by B.W. Anderson and C.J. Payne, and constructed under the guidance of Mr. Pike of the Rayner Optical Co. This innovative prism shape successfully extended the measurable refractive-index range to approximately 1.86, allowing the instrument to identify a broader range of gemstones than earlier models. Compact and practical, the Rayner “Blende” Refractometer represents an important transitional step in the evolution of British gemological instruments and the search for higher-range, more versatile optical designs.

Two other models using synthetic spinel and natural diamonds were also made by employing the same design. 

This object belongs to the museum archives. No unit is available for purchase at this time.