gems, early glass making, Porta, Natural Magick, gem counterfeiting, alchemy, early science, early mineralogy, early gemology, Della Porta, John Baptist

Glass simulants of gemstones were long produced without significant prejudice against their use. However, documentation of their manufacture is scarce due to the secrecy maintained by glassmaking guilds, despite the survival of some late medieval manuscripts that have recently come to light. These manuscripts reveal glass compositions and fabrication recipes that align with the trend initiated by 16th-century “writers of secrets,” who began to disclose technological knowledge to a broader public. Giovanni Battista Della Porta was the first to publish printed recipes for creating glass imitations of gemstones, alongside methods for enhancing natural gem materials. His Magiae Naturalis (1558), originally written in Latin to appeal to upper-class enthusiasts, was widely translated into the vernacular across Europe. The second and much-improved edition (1589), again in Latin, did not gain the same popularity—perhaps because the first edition had already saturated the market or, alternatively, due to the Catholic Church’s increasing restrictions on alchemical practices, which rendered even the title Magiae suspect. Despite these limitations, both editions helped popularize glass “gems” as decorative objects and stimulated their trade. Interest in glass gem-making peaked during the Baroque period, and Della Porta’s treatise was even translated into English in 1658.