To prevent a bad effect from being produced on the optical characteristic of a facing coating by providing a barrier layer of a metal oxide having a thickness of a specified value or less for preventing the diffusion of alkali ions from a glass base on the surface of the glass base.

This device has a transparent glass base, a barrier layer 120 in thickness. or less of a metal oxide on the surface of the base, which prevents the diffusion of alkali metal ions from the glass base, and a metal-contained coating on the barrier layer. The barrier layer preferably has an oxide metal selected from the group consisting of zirconium oxide and titanium oxide. An extremely thin layer of the metal oxide such as zirconium oxide and titanium oxide is formed as an effective diffusion barrier to sodium without compromising the optical characteristic of the glass to be covered. The metal oxide barrier layer is perfectly effective in a thickness of 120 or less, particularly, within a range from 20 to 90, and most effective in a thickness range from 30 to 60.