1 INTRODUCTION

In its broadest sense, a drier, or siccative, may be defined as any material that will enhance the drying properties of oil paint. In the 19th century it was understood that the painters' oils linseed, poppy seed, and nut oil dried by the uptake of oxygen. Driers were seen to be oxidizing agents that accelerated the oxidation of the oil.

The driers referred to in 19th-century artists' literature were metallic compounds, pigments containing these compounds, or varnishes. Around the turn of the 19th century, and for a few decades afterward, the use of ground leaded-glass and smalt was occasionally mentioned. Until the 1860s, the metals most often cited in association with driers were lead and zinc. Very occasionally copper in the form of verdigris was mentioned. Although referred to as early as the 1830s in lists of driers, manganese compounds did not receive any significant notice until the 1860s and were not introduced by name in the artists' colormen's catalogs until the 1890s. Cobalt-based driers were described in a source from the oil paint trade literature published in Britain in 1874 (Riffault et al.) but did not appear in the colormen's catalogs, nor were they ever mentioned in artists' manuals or handbooks in the period of study.

Driers were used in the preparation of the oil itself and in the preparation of separate medial that were added to the paint. They were also added both in the tube and on the palette to slow-drying colors such as Prussian blue, the lakes, and certain browns and blacks. It was recognized that in damp and cold conditions, paint required driers that would not be necessary when it was sunny and warm, so recommendations for driers varied according to the weather and the season. Driers were also recommended for underlying paint layers to hasten their drying prior to further painting.