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. 2015 May 5;5:9842. doi: 10.1038/srep09842

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Photographs of (a) a part of a currency bill and (d) a document under normal light. Photographs taken under illumination at 365 nm (b) PE1 coated currency bill, (c) tick mark made using water on PE1 coated currency bill, (e) letters stamped over the document using PE1 and (f) colour change after spraying water over it.