Q. Can you tell me the difference between overlay and cased glass?

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According to Dictionary of Glass Materials and Techniques, by Charles Bray, overlay is "A layer of glass gathered over a layer of a different coloured glass." Cased glass "usually refers to blown glass which has two or more layers, one of which is either coloured and /or opaque... the layers of colour are usually etched, engraved or cut through to reveal the clear glass underneath. Latterly, sandblasting has become a popular method for removing some of the colour...casing is the basis of cameo glass and a considerable amount of decorative cut glass produced over the years." Therefore you can see overlay is a layer of glass, which is a part of cased glass. 

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AN