The Iron Gall Ink Website

Pre-Treatment Assessment - Microchemical tests

Birgit Reissland, Karin Scheper and Sabine Fleischer (2007)

Spot tests are simple procedures which uniquely identify a substance or a property. They can be done on small samples, even on a microscopic scale. In general an indicator or other reactants are added to a sample. Occurrence of specific reactions will indicate if expected properties or substances are present. Results of spot tests have to be interpreted carefully. For ink corroded artefacts the following tests are recommended:


Non-bleeding test for iron(II)ions

If surplus iron sulphate was used to produce an iron-gall ink, or if the coloured ink complex is not stable and disintegrates over time, “free” iron ions might be present within artefacts. “Free”, unbound, water soluble iron(II) ions are harmful to organic substrates like cellulose (paper) or collagen (parchment) since they catalyse their oxidative degradation, causing discolouration and mechanical decay. 

In order to estimate if iron(II) ions are present and thus form a risk to an artefact, all brown, blue and black writing or drawing inks need to be tested. The non-bleeding bathophenanthroline indicator paper is specific for iron(II) ions and has been developed by the Netherlands Institute for Cultural Heritage (ICN, Amsterdam). This test is very sensitive, reliable and easy to apply. Iron ions can be present in two oxidation states as iron(II) ions and as iron(III) ions. A modification of the test will reduce iron(III) ions to iron(II) ions by applying Ascorbic acid. In this way the potential presence of iron(III) ions can be assessed.


> Risk: free iron(II) ions can catalyze oxidative decay of cellulose


altInstructions: Non-bleeding test for iron(II) ions (pdf)

altInstructions: Preparation of Ascorbic acid (pdf)


  • Order address for the bathophenanthroline indicator paper:
    Preservation Equipment Ltd
    Vinces Road
    Diss, Norfolk
    IP22 4HQ, England
    Tel: +44 (0)1379 647400
    Fax: +44 (0) 1379 650582


References: For more detailed information see

altNeevel & Reissland 2005 (PDF)  

altVuori & Tse 2005 (PDF)


Solubility test for all present media

Media present on artefacts (i.e. writing inks, printing inks, copy pencils, stamping inks) might be soluble in solvents applied during the treatment. Therefore, all media present should be tested in order to get an indication on the risk of loss of media by dissolving (“bleeding”). Solvents used during the calcium phytate treatment are water and ethanol. Presently, several methods are applied for testing the susceptibility to treatment solvents; here two procedures are discussed in detail:


altInstructions: Media senstivity to treatment solutions using blotting paper(pdf)

altInstructions: Media senstivity to treatment solutions using paper points(pdf)

  • Reference: Several procedures for sensitivity tests to treatment solutions are discussed in: Paper Conservation Catalog, Catherine I. Maynor ed., American Institute for Conservation of Historic and Artistic Works, Book and Paper Group, 1994, Chapter 10, sub-chapter 10.4  Spot Tests, p. 60-68.


Paper absorption time

Ink corrosion influences the wettability of paper. Ink-corroded paper areas that are dark brown discoloured are hydrophobic: they hardly take up water. Areas in close vicinity to inks that are light-brown or even not discoloured are usually hydrophilic: they take up water very easily. Wetting an ink-corroded paper consisting of areas of different wettability is quite problematic. Creation of cracks in hydrophobic (ink corroded) areas is quite likely to happen, especially in papers that are weakly or non-sized. A second risk might be expected from heavily surface sized papers. They bear the risk that the surface sizing dissolves during the aqueous treatment and the ink disappears. This risk is serious if leaf casting techniques are to be applied.  

In order to estimate the risk of crack-formation due to aqueous treatment, to judge the intensity of a surface size and to estimate if a re-sizing might be necessary, the time that a paper takes to absorb a drop of water should be determined.


altInstructions:Preparation of calcium bicarbonate using mineral water (pdf)

  • Reference: Several procedures for testing the absorption time of paper are discussed in: Paper Conservation Catalog, Catherine I. Maynor ed., American Institute for Conservation of Historic and Artistic Works, Book and Paper Group, 1994, Chapter 10, sub-chapter 10.4  Spot Tests, p. 62 “A. Water testing”
  • Reference: Reissland 2001