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Solid air fresheners and insecticides that work by evaporation quickly become
useless when left on shelves in shops for too long. Reckitt & Colman’s
answer is an indicator which gives a direct read-out of the product’s condition
(GB 2347350). As usual, a block of water-based gel traps liquid perfume or
insecticide, which steadily vaporises. A hologram covers a window in the
packaging and remains in contact with the gel. When the gel dries out, the
hologram reveals a warning mark.