The production of alum crystal constituted a major manufacturing and international trading market in Europe from late medieval times onward. Its major use was as a mordant, a dye fixative, which had the further property of brightening the colours which it fixed. It had additional uses in leather tanning, paper-making, and medicine. From its early days in the Papal States, where the ‘Roman Alum’ produced in Tolfa supported large communities of miners and traders, its manufacture spread to the German states, to Spain, Sweden, France and Britain.
The process of alum crystal production was a well-understood technique, despite the underlying chemical complexity of the several stages of production, and it appears to be the case that the chemistry of alum and its crystalline form only started to receive sustained attention from chemists around the mid-eighteenth century. This started with Stahl, then continued in Germany in the work of Pott, Marggraf and Klaproth. In Sweden it received further analytical attention from Bergman, and latterly, in the 1790’s and early 1800’s, from the French chemists Chaptal (by that time himself a manufacturer of alum crystal), Vauquelin, Thenard and Roard. My paper surveys this sequence of analytical attention to alum, differentiating the various motives for and modes of investigation exhibited by chemical analysis, and the understandings it produced. It examines particularly the complex of sites and skills which connected factories, fixatives and dyes with analytical technique, and on the competitive intensification in the international alum market which focused and shaped this analytical attention.
