In search for a new lead white: Understanding the historical production processes for industrial-age lead white pigments (1740–1940)

Abstract

In heritage science, lead white pigments are of great significance due to their omnipresence in historical polychrome and finishing layers. However, although lead white dominated the artist's palette from Antiquity until the early 20th century, modern production processes have remained largely unstudied. This paper explores the manufacturing methods from 1740 to 1940, as these differ fundamentally from the traditional ‘Dutch Stack Method’. Moreover, the technological breakthroughs of the industrial-age initiated an intensive search for improved production pathways, as attested by the 185 process descriptions found during this survey of historical textual sources. A thorough understanding of these innovative processes and their ensuing end-products is particularly relevant for the conservation field as recent studies demonstrated that the production method influences the resulting lead white subtype and its painting properties. Drawing on process descriptions in patents, technical manuals and treatises, a classification is proposed based on the underlying chemical methodology; the main categories are methods based on corrosion, precipitation, electrolysis and volatilisation. In addition, the real-life, commercial prevalence of these categories was assessed by studying literature and archival information on large-scale trade and industry. Surprisingly, these findings indicate that, despite the many innovative chemical pathways registered, the lion's share of lead white manufacturers across Europe and North America continued to employ the corrosion methods, which remain the most indebted to the traditional stack method. Nevertheless, a significant number of factories adopted the novel pathways (i.e. precipitation methods), even though the ensuing products were often considered as of lesser quality in contemporary literature.