ブックタイトルConservation and Restoration of Western Paper

概要

Conservation and Restoration of Western Paper

Photo 8 Application of indicator paper for iron ions,National Archives of MexicoPhoto 7 Aqueous chemical stabilization of iron gall inkswith excess of iron ions, National Archives ofMexicoink was not the expected one: "If the Blackis not in it, then add vitriol to make itgood.""And if (the ink) is too pale, add toit a little more copperas and you will have agood ink." 2The damage known as ink corrosionis common in documents with iron gallink with excess of iron ions, and it is acombination of acid hydrolysis and oxidationof cellulose, catalyzed (or accelerated) bysulphuric acid and free iron(II) ions, both3, 10provided by the ink itself. Such processesare cyclic, as iron(III) ions (more stable ions)are constantly reduced to iron(II) ions (moreunstable) in acidic environments, to restartthe oxidation process of cellulose.Another factor that significantlyinfluences the extent of the damage isthe migration of ink components. Bothiron ions and, especially, sulphuric acid,easily migrate from the inked area to itssurroundings in high humidity conditions,due to their affinity with cellulose andwater. 2, 3 Such migration may occur by highrelative humidity in the environment, or bydirect contact with water, either by accident,disaster. Or even inadequate conservationtreatments.The most common effects caused by inkcorrosion are:? Color changes: Iron gall inks withexcess of iron ions (which originallyhad a black color), become dark brown,due to the oxidation of the ink.? Brown discoloration or halossurrounding the inked areas: Oneof the first signs of corrosion, due tothe oxidation of cellulose, catalyzed byiron ions and the migration of sulphuricacid.3, 10? Offsetting: Sulphuric acid can alsomigrate to the reverse of the overlyingpage, producing a brownish mirrorimage of the text on the reverse ofthe document, making it difficult toread and increasing the fragility of thesupport. It is a very common damage49