gems, spinel, Ceylon, Sri Lanka,

Study of the optical properties of red, blue and violet spinels from Ceylon (Sri Lanka), examining their absorption and refractive behavior in relation to color. Schlossmacher presents measurements and observations of differently colored natural spinels and compares their optical absorption and refractive indices, seeking systematic relationships between color and optical properties. The work forms part of his broader investigation of the causes of color in Ceylon spinels, subsequently extended to brown material and to the substances responsible for coloration. It provides an early quantitative treatment of colored spinel using optical measurements rather than color description alone and is particularly relevant to the historical development of gemological research on spinel.