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The ability of a material to block the passage of light. Opacity is the opposite of transmittance. Both are measured as optical density. In paints, the opacity of a pigment indicates its ability to cover, or hide, a color beneath it. An opaque paper can be printed on two sides without image interference. Ceramic glazes must be opaque to cover the clay body. In photography, opacity indicates that amount of light absorbed by the emulsion.

Synonyms and Related Terms

Opazität (Deut.); opacité (Fr.);