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The Use of a Natural Dye in the Formulation of a Thin Coloured Coating on an Aluminium Surface

This paper describes a novel method for the electrolytic colouring of unanodised aluminium. The clean metal is treated using an alternating current in a an aqueous bath containing tin(II) sulphate and the natural colouring matter crocin, the digentobiose ester of crocetin. This coating has a bright grey-greenish-yellow colour about 3 micrometers thick and is suitable for decorative purposes. If the aluminium has been anodised the coating cannot be formed

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