In order to suppress the lead leaching from porcelain tableware, silica-coating on overglaze decoration by the sol-gel process was tried. The silica thin films were dense and it was suggested that the micropores larger than 0.36nm (kinetic diameter of N2 molecule) did not exist. Only in the case a sol aged for a long time, micropore (pore diameter: 0.7nm) formation was observed. By the coating of the silica thin films which had no pores accessible for N2 molecule, lead leaching was suppressed to large extent. In the case of silica thin film with micropores of 0.7nm in diameter, the amount of lead leached was almost the same as that of the specimen without coating. This tendency was due to the easiness of the diffusion of Pb2+ hydrated ion through the coating films depending on the relative size of Pb2+ hydrated ion (0.46nm) and the pore diameter.
