print this page

Ink corrosion (Metamorfoze)

Development of treatment strategies for manuscripts and drawings with iron gall ink.

Kilometres of historical manuscripts and boxes full of drawings with iron gall ink have survived the centuries, often in surprisingly good condition. Is ink corrosion indeed a risk? Some objects do show ink corrosion damage. Why is that?

Manuscript affected by ink-corrosion.

Manuscript affected by ink-corrosion.

Ink corrosion presents two types of damage: reduced readability due to paper discolouration under and adjacent to the ink lines and local brittleness of the paper, which can result in cracks or even loss of material with handling. The fear is widespread amongst collection managers and conservators that manuscripts could no longer be used in the foreseeable future or that drawings could no longer be exhibited due to inherent on-going ink corrosion. Is this fear justified? Research has provided an innovative answer to this question and places the issue in perspective.

Risk Factors

Identification of the damage factors and mechanisms that cause ink corrosion formed the basis for a making a prognosis for future ink corrosion damage. The phenomenological study of more than 300 manuscripts and over 100 drawings has shown that the damage is limited to local areas where the iron gall ink comes into direct contact with the paper with writing or drawing. The acids and metal ions contained in the ink affect the paper only in these places. Usually this is such a small area that no damage occurs. Only with thick applications of ink or extremely thin or poorly glued paper can the paper become completely saturated with ink and thus cause greater damage.


However, this changes fundamentally when paper becomes too moist or wet. A comparison of objects that were artificially aged under 80°C at 50% RH (the recommended relative humidity in museums and archives depots) and 90% RH (the relative humidity after water events and climatic conditions in tropical countries), showed the following: harmful ink components such as acid or metal ions, which for centuries were 'fixed' in the ink lines under normal climatic conditions, were transported directly to the as yet unaffected paper surrounding the ink lines in the presence of sufficient water in the paper.


These harmful ions are invisible. While these degradation processes are immediately visible when caused by artificial ageing at high temperatures, under normal ageing conditions they are not and only after a period of approximately 25 years do they exhibit dark-brown discolouration on and underneath the ink lines. Result: decreased readability and increasing weakness of affected areas. Careless handling leads to a higher risk of cracks and lacunae within the ink lines. In addition to internal factors (opacity, thickness and sizing of the paper, and the ink quantity), water and mechanical stress thus proved to be the two key external factors for the risks concerning ink corrosion.

Inherent deterioration?

The general misconception that all objects with iron gall ink will eventually perish due to ink corrosion is put into perspective by the research results. An explanation has been found for the occurrence of characteristic ink corrosion damage. The objects thus affected have had direct contact with moisture or water through a leaking roof, a flood, fire-extinguishing water or a long transport by sea. They can also have come from tropical regions or have been removed from buildings in war situations and stored under moist conditions.

Act now?

It is vital to determine the baseline risk as the first step in deciding whether to take active or preventive measures against ink corrosion. Note that a description of the present condition is insufficient because it does not indicate the active threat to an object or collection. Only a damage prognosis can clearly define the urgency for action. This also provides a solid foundation on which to base considerations of the cost-effective use of resources.


A damage prognosis tool, the Ink Corrosion Prognosis - Web Service, was developed to provide an instrument for institutions to predict future damage of individual objects by ink corrosion. This tool assists by first identifying objects with a high risk of ink corrosion. On this basis, the tool then facilitates the development of individual treatment strategies with the aim of protecting collections against ink corrosion durably. The identification of the main risk factors of water and mechanical stresses makes it possible to reduce the risk of ink corrosion in a more focussed way. In addition a wide range of preventive measures is presented to guard against careless handling and water damage, and to reduce excessive humidity.

Conservation treatment

In collaboration with the University of Amsterdam a fast and minimally invasive method for consolidating local areas of weakened ink has been developed for objects requiring conservation treatment. This offers an alternative to conventional conservation methods for ink corrosion. The side effects of conservation treatments can be reduced to a minimum through the conscious elimination of damage factors.