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Off-Hand - Formed free hand on the end of a punty of blowpipe. No mold is used.

Opal Glass - Glass that resembles an opal, being translucent and white, with a grayish or bluish tint.

Optical Glass - The glass in lenses and prisms, in which homogeneity, refractive characteristics and the absence of defects such as seeds area of major importance. In many modern optical glasses, lead oxide has been replaced with barium oxide while lanthanum oxide is used for optical glass with low dispersion and a high refractive index.

Overlay - A thin layer of clear or colored glass is folded, formed or coated over another.

Overshot Glass - Rolled molten glass is covered with splinters covering the surface as a final completed surface.