Dichroscopes

A dichroscope is a specialized optical instrument used primarily in gemology and mineralogy to observe pleochroism, which is the phenomenon where certain crystals appear to change color when viewed from different angles. The device was invented in the 19th century and remains an essential tool for identifying and characterizing anisotropic materials.

The basic construction of a dichroscope consists of a calcite rhomb or other birefringent crystal mounted within a small tube, along with a polarizing filter. When light passes through the instrument and strikes a pleochroic sample, the user can observe two different colors or shades simultaneously through the eyepiece. This occurs because the calcite separates incoming light into two polarized beams that travel at different speeds through the crystal structure.

Gemologists commonly use dichroscopes to identify precious and semiprecious stones, as different minerals exhibit characteristic pleochroic properties. For example, ruby and sapphire typically display strong dichroism with distinct color variations, while quartz may show subtle changes. The instrument is particularly valuable for distinguishing between natural and synthetic stones, as well as identifying treatments or enhancements.

Modern dichroscopes are typically handheld devices measuring a few inches in length, making them portable for field work and laboratory analysis. Professional models often feature adjustable focus mechanisms and high-quality optical components for clear observation. Some advanced versions incorporate LED illumination systems for consistent lighting conditions.

While primarily associated with gemology, dichroscopes also find applications in materials science and optical research. The principle behind the instrument relates to crystallography and the interaction of light with anisotropic materials, making it relevant to various scientific disciplines studying optical properties of crystalline substances.