Look for this in a future episode of CSI: Detectives expose a piece of paper, a shard of glass, or even a scrap of fabric to a chemical vapor, and within hours, dark brown fingerprints appear. Scientists in the UK report a new method of fingerprint detection that makes fingerprints on almost any material visible to the naked eye. But that’s not all: They say the same method can also read a sealed letter without opening the envelope.

Researcher Paul Kelly stumbled upon the discovery while studying the compound disulfur dinitride. His team first noticed the compound’s fingerprint imaging properties on laboratory glassware. When exposed to vapors of the compound, even in low concentrations, fingerprints left on the glassware would stain a dark brown. Residues from the fingerprints were causing disulfur dinitride to form a dark brown polymer.

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