Chymical Exotica in the Seventeenth Century, or, How to Make the Bologna Stone

The Bologna Stone, a mineral that became luminescent after chymical treatment, represents one of several "chymical exotica" eagerly sought by natural philosophers of the seventeenth century. Curiously, by mid-century the way to make it luminescent was considered a "lost secret" even though several methods had been repeatedly published. This disconnect between published recipes and experimental failures was explained in part by the investigations of Wilhelm Homberg (1653-1715), later the leading chymist of the Académie Royale des Sciences, and in part by the present author's modern reproduction of Homberg's process. This paper describes both endeavours, and explores the often-overlooked difficulties presented by even "trivial" materials involved in experimentation, and how practical reproduction of historical processes (including visits to important locales) can provide a deeper and more vivid understanding of texts as part of our project to better understand the past. It concludes by reflecting on the importance of maintaining a balance between the material and the intellectual when writing the history of chemistry.