Aluminium Iron Oxide Paint

Non-metallised ferrous components of externally located cultural heritage (building elements, structurally engineered objects, iron and steel bridges, railings, masts and pylons, vehicles or other historical artefacts preserved in-situ) are usually painted in order to protect them from atmospheric corrosion. These are considered sacrificial layers and need to be maintained regularly in order to avoid corrosion of the substrate.

AP, an aluminium iron oxide paint was used on a number of Swedish outdoor iron and steel bridges (Figure 2) and on six radio masts built at Grimeton in 1922-1925. The AP system, a 2 + 2 paint layer system, consists of a red lead linseed oil primer and an top drying oil paint pigmented with micaceous iron oxide and metallic aluminium pigments.

The AP was generally applied manually, either by brush or roller (Edwards 1936; Oskarsson 1937). The system was found to spread rapidly and smoothly, with good leveling properties (Vattenfall 1933, 1956). It was also noted that the AP could be repainted after repainting a previous layer had been performed.

The morphology of the AP was lamellar and the pigment was formed by steel hammer stamping of atomised, pulverised or flaked metallic aluminium powder. The stearic acid residues from the stamping process gave the AP its important characteristic termed “leafing”.

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