A trace amount (0.5 mol%) of CuO-cloped 40Li(2)O-32Nb(2)O(5)-28SiO(2) glass (mol%) exhibits the formation of copper metal layers at the glass surface by annealing at temperatures (530 degrees C) below the glass transition temperature (544 degrees C) in the reduced atmosphere of 7% H-2-93%Ar. The coordination state of copper ions is examined from optical absorption and Fourier transform infrared (FT-IR) spectrum measurements, indicating the formation of Si-OH and Si-H bonds due to the diffusion of hydrogen into the inside of the glass and the reduction of Cu+ and Cu2+ ions. The mechanism of the formation of copper metals at the surface is proposed, in which the key points are the reduction of Cu2+ to Cu+ ions due to the hydrogen and the migration of Cu+ ions in the interior of the glass to the surface. The first finding on copper metal layers at the glass surface might have a potential for practical applications such as electrodes in glass. (C) 2009 Elsevier B.V. All rights reserved.