The metallic (black) print silver is converted to a single-color image by toning processes. The print silver is either replaced with colored metals, or colored metal compounds accumulate on the silver grains. Toned photographs are especially durable with long storage lives, because these silver compounds are less subject to breakdown by environmental factors.
Only photos which are correctly exposed, developed to specification, fixed in really fresh fixer and well washed are suitable for toning. In principle any black and white paper can be toned, however warm tone papers produce the best results. Toning can be either direct or indirect. Direct toning converts the silver image to a different silver compound in one operation.
With indirect toning the prints have to be bleached first. A new image is produced in a second bath, but it consists of a differently colored silver compound. The simplest method is toning with VIRADON. It has the advantage over other toning solutions of not affecting the contrast of the prints. In some cases the prints have to be exposed slightly darker.