METHOD OF MARKING LIQUIDS Russian patent published in 1998 - IPC

FIELD: marking methods. SUBSTANCE: in a method of marking liquids by way of their mixing with a dye, the latter is selected from the group including metal-free or metal-containing phthalocyanines and naphthalocyanines, nickel-dithiolene complexes, aromatic amine quaternization products, methyne dyes, and azulene- quadratic acid-based dyes, which are characterized by absorption maximum region 600 to 1200 nm and/or fluorescence maximum region 620 to 1200 nm. Dye is preferably taken in quantity from 1 parts per billion to 50 ppm. EFFECT: increased marking sensitivity. 4 cl, 7 tbl