Alum and the leather industry

It has been suggested that alum was used to produce leather from at least Egyptian and Babylonian times but recent work suggests that alum was used in the process of dyeing skins rather than for tanning. Lack of definitive evidence for the use of alum for tawing during the Roman period will be referred to. Linguistic studies indicate that the difference between the materials produced by alum and vegetable tannins were recognised, appreciated and exploited by mediaeval craftsmen. The methods employed during mediaeval and later times for the manufacture of alum tawed skins as revealed in contemporary documents will be discussed. Later developments in the modification of tawing processes to give a wider range of leather properties will be mentioned. Recent developments in the production of archival bookbinding leathers and the challenges arising when conserving alum tawed leather artefacts will be summarised.