gems, Arabic mineralogy, al-Biruni, rock crystal, glass

Kahle presents and translates sections of al-Bīrūnī’s eleventh-century Kitāb al-jamāhir fī maʿrifat al-jawāhir dealing with rock crystal, glass, enamel/glass fluxes (mīnā), and ruby glass (adrak), using two manuscripts and emphasizing the value of al-Bīrūnī’s account for understanding the materials and techniques represented among the Fatimid treasures. Rock crystal is described as a transparent, colorless stone prized for vessels, hardness, clarity, and resemblance to water and air; al-Bīrūnī discusses its sources, working, value, inclusions, and supposed formation, including contemporary observations and historical anecdotes concerning valuable crystal vessels. Glass is described as produced by melting quartz or sand with alkali, prolonged firing increasing its clarity and hardness; properly made colorless glass could approach rock crystal in transparency, though its greater abundance and softness reduced its value. Particularly important is al-Bīrūnī’s treatment of mīnā, explicitly described as a type of glass, softer and heavier according to its lead content. He records recipes employing finely powdered quartz or rock crystal with red lead or tin oxide, together with natron or borax-type fluxes, and gives coloring materials: lead compounds for yellow, copper compounds for green, burned brass for red, iron residues for black, manganese for wine-purple, lead white for white, burned gold for ruby color, and lapis lazuli and carnelian for violet. Kahle notes that these descriptions strongly support the interpretation of mīnā in Fatimid inventories primarily as enamel or vitreous flux. The final section discusses adrak, an ancient Alexandrian red or garnet-colored glass reportedly comparable in appearance and value to ruby and whose manufacture was said already to have been lost by the ninth century; al-Bīrūnī preserves several recipes or traditions for attempting its production, along with observations on other artificial colored materials, mosaics, and objects recovered from ancient Egyptian and Yemeni burials.