The Iron Gall Ink Website

Conservation - Proposed methods

Robien van Gulik (1997)

Numerous conservation treatment methods for iron gall ink corrosion have been proposed during the last several decades. Many of these proposed treatments have originated from the field of chemistry of physics, and are not as yet being applied by paper conservators. The following list of proposed conservation methods gives an insight into the directions in research currently explored by conservation scientists.



Electrolysis is a purely physical technique used to remove part of the soluble iron ions and part of the acids present. It is a technique proposed in 1980 (Trobas, 1980; 1987) but not commonly used since as a treatment for degraded objects. In a bath containing an electrolyte as conductor, acids and soluble metal salts split and deposit their acid groups and metal ions at the electrodes. This removes them from the paper. The best results were achieved when sodium polyphosphate was used as the electrolyte: approximately 50% of the soluble iron compounds were removed without visible changes in the ink (Heller, 1993). Another phosphate (tetra natrium diophosphate 10 Hydrate), however, made ink disappear fast (Heller, 1993). Wunderlich too warns for the possibility that phosphates, as complex-builders, can cause degradation of the ink complex (Wunderlich,1994). Electrolysis treats both hydrolysis and oxidation only partially, and contributes nothing to the strengthening of fragile papers except for the slight reinforcing effect of all aqueous treatment.


Radical scavengers

Radical scavengers are compounds that immobilize free radicals, the reactive particles formed by degradation processes. To my knowledge, none of these radical scavengers are at the moment actively used in treatment. Nevertheless, they merit mentioning because natural radical scavengers, such as lignin, protect the paper fibres by oxidizing faster than cellulose. Lignin yellows by oxidation, but it can be imagined that colorless radical scavengers could be added to the paper as a protective shield. Research on radical scavengers with reference to ink corroded objects is being carried out in Lubljana at the National and University Library.


Oxidation inhibitors

Oxidation inhibitors have not, until now, been used in treatment. They stop the oxidation process, but not the hydrolysis, nor do they reinforce fragile papers. Research is at present carried out at the Netherlands Institute of Cultural Heritage in Amsterdam, in an aqueous solution of calcium phytate in combination with calcium bicarbonate. The results look promising; no discoloration of ink or paper was seen. Oxidation inhibitors can, if they stay in the paper, eliminate any iron-II-ions possibly formed in the future by instable iron-III-tannate complexes. Recent research indicates that few of these complexes are really stable. Therefore, the formation of soluble iron-II will continue and oxidation inhibitors will have to be present in surplus to stop oxidation effectively.


Ammonium caseïnate

Ammonium caseïnate is, like gelatine, a protein with mild complexing properties and a strong reinforcing action. Initial tests showed ammoniumcaseïnate to have a positive effect on the strength of paper, artificially enriched by copper and iron compounds.(Porck and Castelijns, 1991). More recent research on ammonium caseïnate, carried out in Amsterdam (the Netherlands Institute of Cultural Heritage) is not yet finished sufficiently to publish results.