Protecting historical documents from corrosive ink
From the Middle Ages up to the 20th century, iron gall ink has been used for writing and drawing. Unfortunately, this type of ink, made from a combination of the galls of oak trees, iron salts and tannin, has serious drawbacks. Iron gall ink corrodes the manuscripts it is written on and has become a major problem for the world's museums, archives and libraries. The decomposition of manuscripts is due to the ink's high acidity and the presence of transition metals, which break down the cellulose contained in the paper. The Inkcor project was set up to learn more about the problem of corrosion and develop the best methods for protecting and preserving important historical and cultural documents. The consortium was made up of experts from a wide range of different fields and included art historians, curators, physicists and chemists. Project partners from the National and University Library of Slovenia developed computer models to determine the main causes of the degradation of documents. Evaluation models confirmed that most decay was due to degradation caused by the ink. The work enabled those involved in document conservation to predict more accurately the stability of historical documents written in iron gall ink. Scientists investigated which factors could affect the condition of a document. They discovered that the most important factors were the thickness of the ink layer, the density of the paper and the acidity or alkalinity of the writing material. Environmental factors such as the conditions under which the document was stored, sometimes for centuries, can also have an effect. Thanks to the work of Inkcor it is now possible to predict the condition of historical documents containing iron gall ink. Curators of museums and archives can use this information to plan the best course of action for protecting the documents in their charge.