Glossary: O

Objective Art

Representational; has recognizable subjects.

Occlusion Shadow

Small, dense areas of shadow occurring at points of contact or proximity, where forms come close enough to each other to interface with the light.

Offset Lithography

A unique photo-mechanical technique in which the image to be printed is transferred to the negative plates and printed onto paper. Offset lithography is very well adapted to color printing.


An ogee is a distinctive pattern with two continuous S-shaped curves narrowing and widening. These two curves form a perfect oval before repeating gracefully. The origins of the ogee can be traced to the Tomb of Cyrus the Great in ancient Persia (559-529 BC.), now present-day Iran.

Oil Paint

Slow-drying paint is made when pigments are mixed with oil, the most traditional linseed oil. The oil dries with a hard film, and the brightness of the colors is protected. Oil paints are usually opaque and traditionally used on canvas. They can have a matte, semi-gloss, or glossy finish. To look at examples of works in oil paints, see the articles under the names of every period from the Renaissance onward.

Oil Pastels

Oil-based drawing crayon.

Oiling Out

Rubbing the surface of a dry painting with a thin layer of medium to make it more receptive to paint. Also called oiling up.

Old Master

Traditionally, a distinguished maker of pictures or sculptures who was active before 1700 — during the Renaissance, Mannerist, and Baroque periods, especially Italian, Dutch, and Flemish artists. Today, the term is also being used to refer to recognized masters of the eighteenth century.

One Point Perspective

A form of linear perspective in which all lines (describing straight edges that go from points nearer to points farther) appear to meet at a single point on the horizon. Also, see the depth and two-point perspective.


The quality of being opaque.

Opaque Object

Is an object that cannot be seen through, whether solid or liquid. It does not allow light to pass through; the opposite of transparent.

Opaque Mediums

In painting, the power of a pigment to cover or obscure the surface to which it is applied. When opacity is incomplete, it can be described as translucence or opaque from 99% to 1%. The equivalent of 0% opacity is transparency.


A white surface having iridescence. In opal gemstones, this "play of color" is caused by tiny spherical formations of silicon inherent in this stone's structure. These spheres and the spaces between reflected white light are much like a diffraction grating spectroscope that separates wavelengths of the various spectral colors. The colors depend on the size and distance between the spheres in the opal's structure.


Term used to describe irregular shapes, particularly those resembling objects found in nature.

Optical Mixing

Blending separate, usually adjacent, colors in the eye.


An artwork that is singular and distinctive from other artworks. Also, the actual, authenticated artwork, rather than a reproduction or copy.

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