Use of a metal compound in coloured toner powder for counteracting fluorescence extinction

A coloured powder, particularly a toner powder, containing thermoplastic resin, fluorescent dye, possibly magnetically attractable material and a compound of a metal of which an anion is diamagnetic. The metal is, for example, calcium, silver, sodium, potassium, barium, aluminium, zirconium, zinc or magnesium. The metal compound is preferably a metal salt and is preferably present in the coloured powder in a quantity of between 2 and 15% by weight The metal compound must be dissolved in the thermoplastic resin (or mixture of thermoplastic resins) or be very finely distributed therein. Metal salts, particularly zinc and magnesium salts, of aliphatic, possibly branched carboxylic acids, particularly carboxylic acids having a hydrocarbon radical with at least six carbon atoms, are preferred. Addition of the metal compound reduces extinction of the fluorescence of the fluorescent dye.