Making and Using Alum in Hispanic Craft Recipe Books from the Fifteenth and Sixteenth Centuries Ricardo Córdoba de la Llave Recipe books and technical manuals from fifteenth and sixteenth century Spain contain abundant references to the use of alum. These citations refer to its primary use as a mordant in dyeing and to its secondary uses, including leather tanning. Reference to its use as a mordant in dyeing is found in the Dyeing Handbook by Joanot Valero, a text written in the dyers’ workshop of Saint Maurice (Valencia) at the end of the fifteenth century. Its use as a material for leather tanning is wit- nessed in the Book of Trades from the monastery of Guadalupe, which also dates to the late fifteenth century, and contains an Ordinances section showing its use for the tanning and dyeing of different hides. Other applications of alum in metal- lurgical processes, illumination and ink making are found in separated recipes con- tained in fifteenth and sixteenth century medical or other manuscripts from Spanish libraries. The term ‘alum’ refers to a number of double-sulphate salts of equivalent chemical composition. The most widely employed was common alum, a hydrated potassium aluminium sulphate. Known in Castile as alumbre and jebe (from the Arabic xep), in Aragon it was more commonly referred to as alum. Alfonso X’s Lapidario, published in the mid-thirteenth century, claims that ‘the stone known by axep and by the Latin alumbre’ was so named because of its ‘clearing and shedding light on everything which is boiled alongside it. If treated with it, dyes take beautiful and clear colour’. 1 Our knowledge of the use of alum in the Iberian Peninsula in the late Middle Ages has increased considerably in recent years, due to the publica- tion and study of a number of Spanish recipe books dated to the late fifteenth and early sixteenth century. Previously, most of our evidence on the use of Ricardo Córdoba de la Llave (rcllave@uco.es) is on the Faculty of Humanities, University of Cordoba, and can be contacted at the University at Plaza del Cardenal Salazar, 3, 14003 Cordoba, Spain. The present work has been conducted within the framework of project HAR2012-37357, El conocimiento científico y técnico en la Península Ibérica (siglos XIII-XVI): producción, difusión y aplicaciones, funded by the Subdirección General de Proyectos de Investigación, Ministerio de Economía y Competitividad (Spain). ICON: Journal of the International Committee for the History of Technology, 21 (2015): 51–65. © 2016 by the International Committee for the History of Technology 03 De La Llave 18/2/16 11:41 am Page 51