Herbert Smith Refractometer No. 2 (c. 1907)

The Herbert Smith Refractometer No. 2, produced around 1907, represents a major refinement of George Frederick Herbert Smith’s early gem-testing instruments. While the first 1903 model established the principle of measuring gem refractive indices using a compact prism system, this second-generation design introduced several significant improvements that advanced the accuracy and usability of gemological testing.

Most notably, Herbert Smith expanded the instrument’s refractive index scale to 1.30–1.80, allowing gemologists to measure a far wider range of natural and synthetic materials with precision. This broader scale made the device much more practical for professional use, accommodating almost all common gem species known at the time.

To support the increased optical range and enhance measurement stability, the No. 2 model adopted a larger, more robust metal casing, providing improved resistance to vibration and easier handling in both laboratory and field settings. Central to the redesign was the introduction of a hemicylinder prism, engineered to deliver a clearer shadow edge and more reliable refractive-index readings by maximizing light contact across the stone’s surface.

As an evolutionary step in Herbert Smith’s pioneering work, the 1907 Refractometer No. 2 marks a significant moment in the history of gemology—transitioning the craft from visual assessment to precise, instrument-based science. This model helped establish the foundation for modern refractometer construction and remains an important artifact in the development of optical gem testing. 

Herbert Smith Refractometer No.2 remained "in production until after the Second World War, before it's manufacture was at least discontinued"*, because of the usability and price. 

This object belongs to the museum archives and is not available for purchase at this time.

*Webster, Robert.  4th edition. "Gems: Their sources, descriptions and Identification", 704, Butterworth & Co (Publishers) Ltd, 1983.