1 INTRODUCTION

THE STUDY REPORTED HERE arose from an investigation of dyes used on mid-nineteenth-century flax sewing thread.1 A review of the nineteenth-century scientific literature narrowed the possible blue dyes used on these cellulosic fibers to indigo, Prussian blue, and logwood (mordanted with iron).2 An identification scheme was needed to discriminate among these three dyes and is presented in this paper.

Flax thread samples were prepared and dyed in the laboratory using documented nineteenth-century recipes and processes. Some of the laboratory-prepared samples were artificially aged and used for characterizing the blue dyes and their possible degradation products. A rapid acid digestion technique was used to release dyes on the fiber into solution. Both spectroscopic and wet chemical techniques were then used to systematically analyze the chemicals removed.