A process for the preparation of particles with controlled dimensions comprising the steps of: (i) providing a laminar substrate having a patterned surface comprising a micro-relief repeat pattern comprising one or more discrete cells, each cell consisting of a floor portion and walls having a height (HW); (ii) depositing organic or inorganic material onto the patterned surface and into the cells to provide a thickness (T) of the deposited material wherein T≦HW (iii) stripping the deposited organic or inorganic material from the surface of the substrate; and (iv) collecting the particles formed from said organic or inorganic material; and a composition obtainable from said process comprising a plurality of particles (P), wherein the number (n) of particles in said composition is at least 10, wherein said particles (P) are platelets exhibiting a planar geometry which is circular or which is made up of a number (x) of planar (y)-sided polygon(s), wherein x is from 1 to 20 and y is at least 3 wherein if x is greater than 1 then said planar (y)-sided polygons are fused along one or more sides thereof, wherein the width (WP) of the platelets (P) at their widest point is no more than about 250 μm and the thickness of the platelets (P) is in the range of 10 nm to 50 nm.