Tanning Chemistry – The Science of Leather

26 November 2009

By Anthony D Covington, Emeritus Professor of Leather Science, BSLT, University of Northampton.Reviewed by Dr Graham Lampard

This book is the culmination of Professor Tony Covington’s ‘30 odd years’ of thinking as a leather scientist. Perhaps surprisingly, although the title intimates that the main body of the book should cover tanning theory, the first point to make is that this is a book about the
science of leather in general. The latest ideas he and his leather research group have developed, the Link-Lock concept of tanning, are also set out in some detail.
As he says in the abstract on the back cover, ‘the aim of [the] book is to provide leather scientists and technologists with an understanding of how the reactions work, the nature of their outcomes and how the processes can be controlled and changed.’ It is an eminently readable book that is a comprehensive treatise on the theory of leathermaking. One omission though is finishing, which gets not a mention. (Is there a single book that covers the chemical and physical nature of finishing?).
The thorough contents page leads the reader succinctly to their required topics, via clear and concise sub-headings. There are references at the end of each of the 20 chapters.
The first 70 pages deal with the raw material, whether it is hide or skin, with the usual definitions and descriptions of the skin’s features and components.
The book then delves into the leathermaking process using the basic process as a guide. Chapters on curing and preservation; soaking; the pre-tanning processes are all succinctly written, with Professor Covington not afraid to throw in physical chemistry equations – the Arrhenius equation popping up, for instance, in the chapter on curing and preservation of hides and skins, in relation to temperature control, while pickling concepts are explained in terms of Donnan equilibrium conditions and Henderson Equations.
Given much of his career was devoted to the investigation of tanning chemistries, there are five chapters on the subject, six if you include chapter 19, which discusses the Link-Lock Concept (odd that it should be apart from the other tanning chapters, but it is such a new theory that one suspects Professor Covington was still developing the ideas as the book was being written). Again the chapters are clearly structured. What constitutes tanning begins proceedings, with definitions for hydrothermal stability, shrinkage temperature and the boil test. An interesting sub-section delves into formulating equations to gain an understanding of the most arcane of stability tests.
There is an overview of the mineral tanning properties of the periodic table a la Nurtsen & Chakravorty’s seminal paper of 1958, and then in-depth reviews of the main tanning elements, followed by chapters on vegetable tanning and ‘other’ tannages. Post-tanning and drying complete the process chapters.
However, that is not quite all, apart from the theory of Link-Lock, another theme that runs through the book, is given a chapter, that of the future of leather processing. This has always been a subject close to the author’s heart and in this chapter he discusses what properties new leathers must have and reassuringly states: ‘much of this information is predictable from leather science and from experience in leather technology.’ The future of chrome tanning, non-chrome tanning for ‘chrome free’ leathers, single tanning options other than chrome, and natural tannages are all reviewed.
The book provides an excellent insight into the role of science in leather production, and I can see it becoming a standard textbook for students and leather chemists, sitting along side the Leather Technician’s handbook and the Leather Technologists’ Pocket Book.

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