| http://www.w3.org/ns/prov#value | - While organic plastic materials, e.g., polymeric materials, have been mentioned hereinabove for use in conjunction with the transparent, smooth-surfaced top layer 4, other materials, e.g., inorganic materials such as glass (e.g., conventional sodalime-silica glasses), alkali metal silicates such as sodium silicate, potassium silicate, etc., can be employed.
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