| abstract |
A method for marking a liquid petroleum hydrocarbon. The method comprises adding to the liquid petroleum hydrocarbon: (i) at least one anthraquinone dye having an absorption maximum in the range from 710 nm to 850 nm selected from the group consisting of 1,4,5,8-tetrasubstituted anthraquinones and anthraquinone dimers; and (ii) at least one visible dye having an absorption maximum in the range from 500 nm to 700 nm. |