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Counterfeiters stamp images onto hot foil to simulate the metal security
strips embedded in bank notes, the security company De La Rue of Basingstoke
admits in GB 2347646. A new kind of security strip should spoil their game. The
strip is made from polyester, with a hologram on one side and a text message
printed on the other. The text is coated with a pigment that becomes transparent
when heated above 35 °C. When the bank note is viewed at low temperatures,
only the coating is visible because the pigment obscures the text. When the note
is warmed, the coating becomes transparent and the text message appears, proving
the note is genuine.