ABSTRACT
Use of chemicals for coloring of materials has deep roots: cave painting, staining of the skin, and dyeing of textile materials. In ancient times these were based on naturally occurring pigments and dyes. This chapter describes the application of dyes in the diverse areas where coloration is employed, and also addresses the question of how variations in the physicochemical make-up of dyes can lead to changes in their patterns of cellular localization or affinity for different substrates. Identification of cell types in samples of dispersed cells constitutes a major area of diagnostic use of dyes. The physicochemical basis is that in some compounds, many of them dyes, photoexcitation leads via the singlet excited state to a population of reasonably long-lived triplet excited state molecules. Particulate and insoluble, pigments are generally used as coloring agents for paints and surface coating media such as printing inks. They are also used in textile printing and for bulk coloration plastics and rubber.
