The inherently inert character of soda-lime-silica container glass is discussed, specifically its resistance to water attack and light transmission. Glass is a complete barrier to liquid, vapours or gas transfer. Aqueous foods may extract minute amounts of silica and the alkaline oxides, soda and calcia. This mechanism involves formation at glass/liquid interface of an adherent hydrated silica film, limiting the depth of reaction. Minor elements, if present, may appear in parts/billion. Glass will transmit near-UV and increasing amounts of visible light into the red spectrum, the former considered to be most active since many foods show light absorption in this range. As a packaging material, glass has superior performance characteristics compared to metallic, plastics, composite or other barrier structures.
