This thickener is entirely suitable for the preparation ofpigmented compositions that are stable over time, such as nail varnishes.In the thickener of the invention, the term hydrocarbon-based alkyl chain is understood to refer to a linear or branched chain preferably containing from 1 to 24, more preferably from 1 to 10, better still from 1 to 6 and more especially from 1to 3, carbon atoms.