Making Yellows Last with Nitric Acid: Exploring Colour Permanence in Art and Knowledge, 1600-1850.

Nitric acid became commonly available in the seventeenth century. Since then, it held the interest of chemists, especially those interested in the art of dyeing. Due to what is now called the xanthoproteic reaction (from Greek xanthós, describing shades of yellow), nitric acid produces a stable yellow colouration in proteinaceous materials, such as wool, silk, and bones. The chemistry of this reaction is well understood today. Less well-known is that it held the interest of dyers in the past. Dyers considered the ability of nitric acid to give a yellow colour to certain substances a solution to giving materials a durable, that is, a lasting, yellow colour. Yellow, indeed, posed a problem in the art of dyeing. Before the discovery of synthetic dyes in the mid-nineteenth century, there were no organic yellow dyes with long-term colour stability. Using historical dyeing manuals and chemistry treatises, combined with our practical engagement with the processes they describe, this paper traces how, between the seventeenth and nineteenth centuries, dyers explored nitric acid while examining the durability of yellow colourations. Based on these explorations into nitric acid, the chemical arts developed theories about the nature of colour, and about the causes for its relative permanence.