gems, corundum, History.1, diamond, beryl, emerald, sapphire, ruby, topaz, quartz, spinel, garnet

Sinkankas: In this early Spanish work, Mosquera deals with the theoretical & practical aspects of weighing and valuing precious stones, but supplies much highly interesting ancillary information. There are eight books, the first & second on diamond, third on rubies, fourth on emeralds, fifth on sapphires & topazes, sixth on amethysts, spinels, garnets, among others, seventh on pearls, and the last book comprising miscellaneous information on the stones and pearl previously treated. The instructions show readers how geometrical principles may be used to accurately estimate weights of cut gems that otherwise could not be handled singly, e.g., as gems in mountings. Mosquera also tells how to correctly judge cutting proportions and thus aid in arriving at more accurate estimates of value, here referring the reader to the folding engraved plate which shows geometric diagrams based on the octahedral crystal of natural diamond, its cross-section, various geometrical forms, diagrams of several cut gems, a balance with weights, scales for measurement, etc., all aimed at facilitating weight estimation, correct cutting proportions, and values. Many tables of weight vs style of cut are incorporated in the text with much of the information similar to that given by Jeffries in his A Treatise on Diamonds and Pearls, 1750, which see, and which may have been consulted by Jeffries, although we have no sign that Jeffries even knew of the existence of Mosquera’s book. A rare work.