Definitions for "Flashed glass"
Keywords:  dipped, molten, darker, glass, glazier
A white or clear glass to which a thin layer of colored glass is added on top
Natural pot-metal glass colored blue or red was too dark to transmit much light, so the medieval glazier hit on the technique of applying or "flashing" a thin layer of the colored glass on to a sheet of white glass, thus getting over the problem.
Glass objects dipped into molten glass to give them a fine outer layer, thinner than on cased glass, which is often in a contrasting colour. The flashing may be cut or ground away in a pattern to expose the layer underneath.