Skin care against ultraviolet light is attracting increasing attention [1, 2]. Many studies have been devoted to developing new functional materials for inclusion in new sun screen products [3, 4]. Mica, consisting of layer silicate, is divided into different minerals, e.g. muscovite, sericite, illite, phlogopite etc. [5]. Their properties are dominated by the crystalline structure, and the shape and size of particles. The surface charge of sericite is negative in aqueous systems, with a few silicon atoms being replaced by aluminium. The layers are stacked to form a three-dimensional structure. These thin mica platelets are used by many kinds of industries because of their unique properties, i.e. gloss, transparency, adhesiveness, texture and high whiteness [6±8]. Successful delamination will lead to these promoted unique properties. However, delamination of mica is technically not easy. Size determination is problematic because of its high anisotropy. On the other hand, intact mica are modi®ed with titanium dioxide called pearl or uoride [9]. These treatments result in better properties due to thin platelets. Furthermore, ultraviolet screening ef®ciency increases due to coated screening agent, being previously dispersed. The purpose of the study reported here was to establish optimum delamination of sericite with simultaneous modi®cation with titania sol, and to determine the average diameter and average thickness of sericite platelets. We attempted to ®nd a delamination method and a modifying condition with titania sol for sericite as an ultraviolet ray screening agent. Sericite (Sanshin Kogyou Co., nominal median diameter 6.8 im) was used as a starting material. A suspension of sericite for wet ball milling was prepared by dispersing 0.15 vol % in 0.01 M NH4Cl aqueous solution [10]. Clear titania sol was prepared by hydrolysing 0.5 M titanium isopropoxide (Wako Pure Chemical) alcohol solution with 0.1 M HCl alcohol solution [11]. The size of the sericite platelets was determined from the average Feret diameter, dxy, i.e. those corresponding to the average diameter of the platelet, and the average thickness, dz. Details of the characterization of the platelets is given elsewhere [10]. Adhesion of titania sol to sericite was observed by electron probe microanalysis (Jeol, JXA-8800). The amount adhered was determined by X-ray uorescence analysis (Jeol JSX-60P). The amount of free titania sol in the supernatant was determined by atomic adsorption spectrometry (Video 12). Representation transmission electron micrographs of the cross-section are shown in Figs 1 and 2 for the intact and delaminated samples. Delamination was carried out with 18 mg gy1 titania for 24 h. The intact sericite consisted of a multilayer structure with a number of stacked platelets. However, the delaminated sericite consisted of the thin platelets, separated from the thick multilayer structure. Part of the thin platelet was wavy and distorted. This indicates that delamination of sericite caused simultaneous damage to the layers. The thickness distribution of the platelets is shown in Fig. 3. The average thicknesses of intact and delaminated sericite were 0.945 im (average from 17 observed thicknesses with a standard deviation of