Zinc Oxide in Oil-Based House Paint: Insights from a Paint Chemist’s Notebook Dated 1949

Abstract

The Dulux Archives in Melbourne hold a set of four laboratory notebooks written by Brian Roberts while a trainee paint chemist at British Australian Lead Manufacturers (BALM) Pty. Ltd. in 1949. This paper focuses on information contained in the notebooks detailing company testing and practical tools for managing known zinc oxide reactivity in oil-based house paints. Acceptable application and weathering properties of zinc oxide in oil paint formulations emphasized good quality larger particle size zinc oxide pigment at correct pigment volume ratio, appropriate driers and importantly, the use of stand oil. The notebooks provide a prompt to consider the effect of the stand reaction on linseed oil acids and subsequent soap formation. Although stand oils can contain a high proportion of acids available for reaction with zinc ions, due to Diels-Alder reactions during the stand process a proportion have likely become cyclic. The subsequent cyclic zinc carboxylates may inhibit aggregation and crystallisation and thus may be less problematic in paint films than zinc carboxylates of the straight chain fatty acids found in untreated linseed oil - rendering zinc oxide in stand oil more stable.