| http://www.w3.org/ns/prov#value | - l with atomic disorder, the top layer may be provided as an in situ generated top layer by virtue of its thickness and/or composition changing on contacting an alcohol or water based electrolyte, so as to produce an interference colour which differs from the initial colour of the base layer. [0074] Most preferably, the top layer is a thin film of a composite material formed by co-, sequentially or
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