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Deliberately Colored Glass

Heavily weathered "onyx" ware
Early 1st century A.D.

In certain deliberately colored glasses the progress towards disintegration moves quite rapidly. For example, during weathering of opaque red glass (see Coloration), the cuprous oxide needles that cause the coloration are easily converted to a green crust of copper chloride. During the weathering of "onyx" ware (see Mosaic/Cast), the creamy opaque white swirls become heavily pitted while the amber layers between them remain resistant.