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The way medieval craftsmen made the first pocket Bibles

27 November 2015

by David Keys

John Rylands Library, University of Manchester

SCIENTISTS have cracked a medieval biblical mystery.

For hundreds of years, historians and others had believed that the very finest medieval parchment —specifically used in the 13th century to make lightweight, portable Bibles — was made from the skins of aborted, stillborn, or newborn calves. Some even thought they were made of rabbit or squirrel skin.

But now, after scientists from the University of York, led by Dr Sarah Fiddyment and Professor Matthew Collins, carried out detailed tests on 72 of these ultra-lightweight handwritten medieval Bibles, they discovered that these super-fine religious treasures were, instead, made of the skins of adult goats, adult sheep, and eight-week-old calves.

The medieval biblical production-line constituted Europe’s very first large-scale publishing industry. Over an 80-year period (roughly 1220 to 1300), between 20,000 and 30,000 handwritten Bibles were made. In aggregate, that involved the manufacture of millions of sheets of ultra-thin lightweight parchment — just 1/15 (and sometimes even 1/18) of a millimetre thick.

It is not known whether the medieval Bible-makers tried to con their clients into thinking that the precious books were made of pure newborn calfskin. But the ultra-fine products were, in medieval times, known as “abortivum”, suggesting, at least, that the parchment was marketed as being fine and pure as the skins of aborted calves.

The market for super-fine lightweight portable Bibles was short-lived. It was created by the huge expansion at that period in the number of highly mobile mendicant friars and in the number of university students. The main mendicant orders of preaching friars were established in the first half of the 13th century — and the first dozen great European universities were all set up in Italy, France, England, and Spain between 1088 and 1243.

But an economic downturn at the end of the 13th century, partly induced by climate change, brought production to a halt. Each portable Bible had cost the equivalent of several thousand pounds to buy — and the friars and students could no longer afford them.

By scientifically testing a 3.6-per-cent sample of the 2000 surviving 13th-century lightweight Bibles, the scientists reckon that 68 per cent were made of calfskin (many from France, and probably some from England), about six per cent from adult sheep (mainly from England), and 26 per cent from adult goats (mainly from Italy and southern France).

In order to make goat, sheep, and eight-week-old calf parchment look as fine as if it had come from newborn calves, the medieval artisans had to immerse the skins in alkali-rich liquefied lime so as to get rid of the fats in the skins by transforming the lipids into a form of detergent. That natural soap not only helped thin the skins, but also whitened them, by dissolving all the ingrained grime and stains.

The alkali in the lime also served to remove the thousands of tiny hairs in the skin — by weakening the chemical bonds that hold protein molecules together.

Apart from immersing the skins in lime, the artisans also stretched them on wooden frames, scraped them with special tools, and spent many hours rubbing them with volcanic pumice stone to further thin and smooth them.

The new research has involved protein analysis and hair-follicle pattern analysis, in order to determine the species of the animals used, and how old they were when slaughtered.

The revelation that parchment was mainly manufactured from eight-week-old calves, and adult sheep and goats, and not from newborn calves, shows for the first time that 13th-century Bible production was actually a lucrative by-product of the food industry.

The director of the research project, Professor Collins, said: “By carrying out detailed scientific tests on a substantial sample of medieval lightweight portable Bibles, we have effectively turned what had been regarded as purely art historical objects into new archaeological data.

“This has enabled us, for the first time, to more fully understand the birth of Europe’s first commercial book production industry.”

Much of the research so far has been published online this week in the Proceedings of the National Academy of Sciences.

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