The present invention relates to pigments whose particles have a length of from 2 .mu.m to 5 mm, a width of from 2 .mu.m to 2 mm and a thickness of from 50 nm to 1.5 .mu.m and a ratio of length to thickness of at least 2:1, the particles having a core of a metallically reflecting material having two substantially parallel faces, the distance between which is the shortest axis of the core, comprising (a), optionally, on one parallel face of the core, an SiO.sub.y layer wherein 0.95