Polycontrast is the proprietary brand name used by Kodak for its range of variable contrast black and white photographic printing papers, describing papers whose contrast grade can be varied continuously across a wide range by changing the colour of the enlarger light used to expose them, rather than requiring the darkroom printer to stock and use separate fixed grade papers for different contrast requirements. The Polycontrast name has become closely associated with the concept of variable contrast printing papers more broadly, in the same way that several other proprietary product names have become generic descriptors for the categories of product they represent.
Variable contrast papers such as Kodak's Polycontrast range achieve their adjustable contrast characteristics through the incorporation of two distinct light sensitive emulsion components within a single paper coating, each sensitised to respond to a different colour of light and each producing a different contrast grade when exposed. One emulsion component is sensitised to blue-violet light and produces a high contrast response when exposed, while the other is sensitised to green light and produces a low contrast response. By varying the colour balance of the enlarger light between blue-violet and green - using a set of Kodak Polycontrast filters, a variable contrast filter system such as the Ilford Multigrade system, or the colour filtration controls of a colour enlarger head - the printer can vary the relative contribution of the two emulsion components to the final print and thereby control the contrast of the result across a range equivalent to the full range of fixed grade papers, from the softest grade 0 through to the hardest grade 5 in half grade increments.
The practical advantages of variable contrast papers like Polycontrast over fixed grade papers are considerable, and were quickly recognised by both professional and amateur darkroom printers following their commercial introduction. A single box of variable contrast paper effectively replaces a complete stock of five or more separate fixed grade papers, reducing the cost, storage space, and logistical complexity of maintaining a fully equipped darkroom. The ability to adjust contrast in half grade increments by selecting intermediate filter values provides finer contrast control than the full and half grade steps available in fixed grade paper ranges, allowing more precise optimisation of print contrast. Variable contrast papers also enable the use of local contrast control techniques, in which different areas of a print are given different contrast grades by changing the filter setting during dodging and burning, allowing highlight and shadow areas to be printed at different contrasts within a single print for more precise tonal control than fixed grade papers can provide.