As colour ink-jet printers get better, it is becoming ever more expensive to foil banknote forgers. The latest wheeze, from paper manufacturer Landqart in Switzerland (world patent filing WO 2004/104277), is to embed fine, photoluminescent polymer fibres in banknote paper. These 3-millimetre lengths of cellulose are coated with a UV-sensitive dye such as stilbene.
Landqart found that if the cross section of the fibres is a squashed oval or a flattened rectangle, they rise to the surface of the cotton-based banknote paper pulp as it dries. That side of the paper then shows bright specks of light…
