multigrade

Definition: Adjective: (1) ~ paper: black & white printing paper whose contrast grade varies with the composition of light. * Also known as variable contrast or vari-contrast paper. (2) ~ enlarger: one suitable for working with multi-grade papers by offering a specially designed light-source. (3) ~ head: light-source for enlarger designed for multi-grade papers, either using a filter in front of one lamp or varying the mix of light by controlling two lamps -- usually specified so that changing grades does not alter exposure. How multigrade works The coating of Multigrade or variable contrast papers are Inter-mixed emulsions of blue-green sensitive and blue-sensitive silver halides. Both have the same contrast and the same speed to blue light, but the blue-sensitive parts are less sensitive to green. When you expose the paper to blue light, the whole emulsion wakes up: adding the two components together gives a high-contrast result. Green light at first only affects the blue-green sensitive part and the blue part is naturally much slower in speed: the contrast is therefore that of component emulsions alone.

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