Longterm Outdoor Exposure of Anodic Coatings Coloured by Precipitation of Inorganic Pigments

Abstract

SUMMARYBetween 1954 and 1958 the authors undertook a large scale investigation into methods of colouring anodic coatings without the use of water soluble dyestuffs. Part of this work involved colouring by precipitating inorganic pigments into the pores of anodic coatings produced by sulphuric acid or oxalic acid anodizing, and the techniques employed were reported1 at the time. Following the recent closure of the laboratories where the work was originally undertaken, the results are summarised for up to 21 years of outdoor exposure. The following new colours can be recommended for architectural use: a green, a Prussian blue, a yellow-bronze, and a Chromate yellow. After exposure for 21 years in an industrial environment the anodized surfaces are in good condition despite considerable loss of film thickness due to erosion.