Art Terms Glossary beginning with O
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- Offset Lithography
- The image is transferred from the stone or plate to a roller on the press which then prints the inked image onto the paper.
- Oil print
- A print produced in pigment or ink applied with a brush, based on the principles of lithography (the repellent action of oil and water). A sheet of paper coated with a gum emulsion or gelatin and made light-sensitive with potassium bichromate is exposed to sunlight under a negative. The emulsion hardens where exposed to light and rinses off in where light could not penetrate. The areas that wash away are then colored with pigment or ink, and the amount of water retained by the emulsified surface determines the density of color on the image. From the 1860s to 1910, many processes were invented for printing images in pigment rather than silver and other metals. The oil pigment process was appealing because images in pigment are essentially permanent. They are not susceptible to the fading, discoloration, or deterioration common in silver prints and, because of their color range, look like work in other media such as crayon, charcoal, or watercolor. The Rawlins oil pigment print, a variation of the oil print, is made on a sheet of paper coated with a gelatin or gum emulsion, sensitized to light in potassium bichromate, dried, and contact-printed under a negative in sunlight. After exposure it is washed and placed on wet blotting paper for the pigmentation stage, where pigment or ink is applied with a special brush. The color penetrates the areas that have absorbed the water (the shadows), not those made water resistant by the hardened gelatin (highlights). The look of the final print depends on how much pigment or ink is applied, either over the entire surface or only to specific areas. The process was invented by G. E. H Rawlins (active 1900-1920s) in 1904. The look of the final print depends on how much pigment or ink is applied, either over the entire surface or only to specific areas. The process was invented by G. E. H Rawlins (active 1900-1920s) in 1904.
- Orpiment
- A soft, yellow mineral composed of arsenic trisulfide. Orpiment occurs naturally, often in association with realgar - a soft red mineral also used as a pigment. It ranges in color from a bright lemon yellow to orange.
