J. H. Steward Dichroscope (c. 1890–1910)

This dichroscope, signed J. H. Steward Ltd., dates to the late nineteenth or early twentieth century, circa 1890–1910. Founded in 1852 and based in London’s Strand, J. H. Steward was a prominent maker and retailer of scientific, optical, and surveying instruments during the Victorian and Edwardian periods. The firm supplied precision apparatus to professional scientists, educational institutions, and members of the British trade, and was known for high-quality brass construction and fitted wooden presentation cases, as seen in this example.

The dichroscope is a handheld optical instrument used to observe pleochroism in doubly refractive gemstones. By employing a calcite (Iceland spar) prism, the instrument separates light into two polarized rays, allowing the observer to compare two color images simultaneously. This capability assists in identifying anisotropic gemstones such as tourmaline, sapphire, and zircon, and in distinguishing them from singly refractive materials. In the late nineteenth century, before the widespread availability of advanced spectroscopic tools, the dichroscope became an essential diagnostic device in the emerging discipline of gemology.

This Steward example, preserved in its original wooden case with fitted interior compartments, illustrates the craftsmanship characteristic of British optical instrument manufacture during the period. Its robust brass body and precision fittings reflect the artisanal production methods of London’s scientific instrument trade. As an early commercial dichroscope, it represents the professionalization of gemstone testing at a time when gemology was evolving from trade practice into a structured scientific discipline.

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