The elusive ingredient for spinning wool into gold

The history of this book is unlike that of any other. Its Spanish author, Felipe Ruiz Mart!n, the favoured disciple of Fernand Braudel, wrote it in French for publication in 1959 and then, without explanation, suppressed it at the printer's proof stage. It is finally published translated, ironically, into the author's own language.

Unfinished, it is a time-capsule of scholarship, locked in a mind-set and bibliography of half a century ago. The edition is sprinkled with errors, none serious. The author's appraisal of his field, the alum trade during the Renaissance, is typically unpretentious: "The alum of Mazarrón, Rodalquilar, Cartagena has served as a guide to summarise, or better to outline, the European economy in the 16th century." In reality, the names of these Spanish mines disguise how cosmopolitan the trade was, transcending religious frontiers, and with a creaking structure of credit finance that presages modern commercial banking. Ruiz Martín's achievement is to show how this evolved out of late medieval seigneurial exploitations, to become an instrument of foreign policy, its control contested between rulers and the mainly Italian entrepreneurs who negotiated the terms of distribution.

Alum was the indispensable fixative for dyeing quality woollen fabrics. As the mines were remote from the industry base, the trade was inevitably international. Ruiz Martín painstakingly pieces together the myriad sources that establish this, with a cement of documentation from the Crown Archive of Castile (Simancas). The main medieval supplier, Byzantium, lapsed in 1453. Over the next 150 years its successors, Tolfa (the Papal mine) and Spanish producers battled to monopolise the trade. The rivalry was mirrored by that between Flemish centres over importation. The role of England was as trafficker in Turkish alum, and reluctant payer of the Papal surcharge. Such a sentiment may have contributed to the early predominance of Mazarrón.

The 1562 production peak was followed by a slump coinciding with the Netherlands revolt. However, an unsold surplus had already accumulated, so causes of decline have to be sought within the trade. A major factor in the constant jockeying of the interested parties to secure their profit margin was the Spanish prohibition of exportation of precious metal, which made the credit system inherently fragile. Explaining this is at once Ruiz Martín's strength and his weakness. His handling of documentation is enviable, but the tale told is ultimately labyrinthine.

Much remains unelucidated: for example, the Crociata (the Papal monopoly that purported to milk the alum trade to fund recapturing Byzantium); even the basic difference between earth alum and rock alum. The co-owner of Mazarrón, the poetic first Marquis of los Velez, and the attempt of the second Duke of Alba to oust him, barely impinge. The parallel wool trade is not referred to, nor the pre-Tolfa interlude 1453-62. The research of Charles Singer is ignored. For the aspiring economic or political historian, is it worth learning Spanish to read this torso of a book? Yes. It is pure insight, and Ruiz Martín mastered seven languages to research it.

Edward Cooper is reader in history, London Metropolitan University.