Patent ID: 7381758

Claim:
A method of treating an optically variable pigment having a stack of planar layers, said stack of planar layers comprising at least one reflective layer and at least one dielectric layer, and at least one layer of a semitransparent metal layer made of Cr, said reflective layer and said dielectric layer having at least one chemically exposed edge surface and being corrosion susceptible said method comprising steps of (a) dissolving a passivating agent selected from the group consisting of organic esters and fluorinated organic esters of phosphoric acid having the structural formula (Rf—CH2-CH 2 —O) x P(O)(OH) y wherein: Rf=F—(CF 2 —CF 2 ) z x=1 or 2 y=2 or 1 x+y=3 Z=1 to 7, in an organic solvent; (b) mixing water into the solution provided in step a); (c) adjusting the pH of the composition obtained in step b) to a value between 7.0 to 9.0; and (d) dispersing said optically variable pigment into the composition obtained in step c) while keeping the pH value at 7.0 to 9.0.