COMPARISON OF INK WRITING ON DOCUMENTS BY MEANS OF PAPER CHROMATOGRAPHY.

This article investigates the comparison of ink writing on documents by means of paper chromatography. The examiner of questioned documents is frequently faced with a problem involving ink. Ink identification has many facets, and the problems which arise may have many forms which may require different approaches to a solution. Among document examiners it is generally understood that ink is usually a multicomponent mixture possibly containing a permanent factor such as iron gallotannate or carbon and one or more dyes to give desired color effects. In modern inks, the variety of colors or dyes which may appear in a particular ink is sometimes surprising especially with washable and permanent blacks. In the examination of questioned documents it is often necessary to investigate the properties of the ink used in the writings on the document. One of the purposes of such investigations is to determine whether or not two writings were made with similar or different inks. Chemical methods of analysis differentiate the inks into types depending upon the presence or absence of metallic salts, reaction with acids, bases, and oxidizing and reducing agents. These methods seldom differentiate between two inks of the same type; therefore, unless the tested inks are of different types or differ in their metallic contents, the results are often inconclusive. Chemical methods have the disadvantage of being difficult to demonstrate in court and of exposing the document to the risk of accidental damage from chemical reagents.