Despite intensive research, the origin of iron gall ink, i.e., the point at which it was discovered that a mixture of an iron-salt and a tannic acid-containing material could be combined to utilitarian ends, still remain a mystery. Around the 7th century, either the Jews or the Moors introduced iron gall ink to central Europe. Iron gall inks offer several advantages over carbon-based inks; they are easier to prepare, they do not contain large particles that block up the quill, and the ink need not be constantly stirred. The main advantage, however, is that once written, the characters remain indelible for centuries. This article explains the structure of the iron gall complex, the appearance of historical inks, and the chemistry of historical iron (II) sulphate. Also discussed are inks with copper sulphate, gallotannins, and brown inks (a forgotten aspect of ink corrosion). The author advises that even though an understanding of the chemistry of iron gall ink and ink corrosion has increased significantly in recent years, the solutions for the treatment of the deteriorated objects are still in their incipient stages. When analyzing the damages, many more factors must be taken into consideration. The contamination of historical iron (II) sulphate with copper sulphate and zinc sulphate should be given special attention. Future investigation should also focus on the organic gall compounds and the influence of deterioration products themselves on the phenomena of ink corrosion. 6 figures and 31 references