Type of ink blamed for the destruction of historic documents

Curators around the world are struggling to prevent the destruction of tens of thousands of historical books and manuscripts, including sketches by Leonardo da Vinci and Rembrandt, handwritten music by Bach and Handel and the American Constitution. The documents are under attack from an unusual source: the ink used to write them.

A recent survey suggested that 80 per cent of European archives are affected by the unfortunate paradox of iron-gall ink, which is slowly eating away the work it was meant to record. The British Library, which is trying to preserve rare work from Roman times to first drafts by Dickens, is gravely concerned about the problem.

"It takes several hundred years for something to be completely eroded," said David Jacobs, a senior conservator who has been at the British Library since 1982, and in conservation for more than 30 years. "But before that it becomes increasingly fragile, so you can't lend it out."

Iron-gall ink was used by the Romans and produces the characteristic black familiar on manuscripts dating back hundreds of years. It was favoured over carbon-based inks because it would "bite" into the page, and could not be washed off. That made it a favourite for official documents, including the American Constitution, because it was proof against forgery. But, the ink's constituents – extract of gall nuts mixed with gum arabic and iron sulphate – contain the secret of the documents' destruction. New Scientist magazine, which highlights the risk to book collections today, warns: "Open an old book and disconnected letters can fall into your lap, the paper a lace doily with a mass of sentence-shaped holes."

The reason is that the iron in the ink reacts with the air over time to produce oxygen radicals – highly reactive individual atoms of oxygen that will react with anything they touch. At the surface of the manuscript a chain reaction breaks cellulose down into smaller molecules with the result that the paper yellows and becomes brittle. Ink rich in iron sulphate makes the paper break down faster. The problem is worst in music manuscripts, explained Mr Jacobs, because "musicians were constantly making changes, which means more ink on the page."

The British Library, together with organisations around the world, is seeking ways to stop or at least slow down the reactions. And the good news is that there may be a solution – literally.

Two scientists from the Institute for Cultural Heritage in Amsterdam have developed a system which bathes the affected pages in a solution of phytate, a natural antioxidant from seeds, which is used to treat cancer. The phytate works by reacting with molecules that would otherwise react with oxygen to produce free radicals, which inside a human cell can cause cancer, but on a page rots it.

"This is the only thing that seems to stabilise the iron," said Mr Jacobs. "It seems the best option at the moment."

Elmer Eusman, senior paper conservator for the US Library of Congress, said: "It's a very elegant method. It doesn't make a coloured solution, it doesn't attack the ink itself – it has a lot going for it."

The phytate is still being tested. None of the archives has yet been treated with it.