Comparison of Writing Inks by Paper Chromatography

Abstract

Questioned document analysts have often been confronted with the problem of determining whether all of the writing on a particular document or on different documents was done with the same ink. Solutions to these problems have heretofore been undertaken by various methods such as the use of chemical reagents, infrared photography, and spectrography. These methods and their limitations are well known to the profession and need not be discussed here. Recently, a new approach known as was introduced in the field of ink examination. This method has already been found a valuable aid in many cases and offers the advantage, among others, of permitting results of laboratory tests to be graphically illustrated before courts of justice. Weil traces the origin of the method of filter paper capillary analysis to the German scientist F. F. Runge who, in 1850, described the use of blotting paper for the analysis of mixtures of dyes. In 1885 J. U. Lloyd submitted a report on filter paper partition to the American Pharmaceutical Association. Pliny (23-79 A. D.) is reported to have used a test paper for detecting ferrous sulphate. It was not until 1951, however, after extensive research, that the merits of the technique in relation to the examination of writing inks was publicly revealed. 2 During the 17th, 18th, and the greater part of the 19th centuries, iron-gall inks were used almost exclusively in the United States. The 20th century brought about the use of increased amounts of aniline dyes (unavailable before 1860) and less iron and tannin. The chromatographic method of analysis is especially applicable to dye-base inks. Comparisons are further facilitated by the frequent occurrence of several dyes in a single ink. Ink in Liquid Form. Two inks in liquid form can be readily compared by chromatography using only distilled water and filter paper.