The primary difference between black and white and color prints is in the image-forming material. There are two types of color photography: chromogenic and nonchromogenic. Modern chromogenic color photographs are the most common and use organic cyan, magenta, and yellow dyes as the image-forming material. The chromogenic process (introduced in 1935) forms a black and white silver image, which causes the developing chemical to react with dye couplers to form a dye image around the black and white image. The black and white image is then removed with bleaches and the color image is fixed and washed.
A different type of dye (azo dye, which is much more stable) is used in nonchromogenic photography (e.g., Cibachrome and Ilfachrome), which was introduced in 1955. This process is known as silver dye bleach and produces photographs with excellent dark stability and better light stability than chromogenic photographs. However, chromogenic materials are cheaper and more versatile, and thus much more common.
Dye fading—Unfortunately, the dyes used in chromogenic processing are inherently unstable. The three dyes do not fade at different rates, so there is often an imbalance of color in deteriorated color photographs (e.g., the cyan dye fades first, leaving the photograph with a reddish tinge). It is also very important to note that some dyes that fade faster in the light may be more stable in the dark, and vice versa. In general, early color photographs were very unstable; many lost 30% of their dyes (30 percent loss is the accepted point at which deterioration becomes evident) within 10 to 15 years. Even color photographs from the 1980s will reach the 30 percent mark within 20 years. Advances in dye stability were made during the 1980s and 1990s, and contemporary color materials can be expected to survive 30 to 50 years at room temperature.
Highlight staining—This appears as a yellowish staining in the highlight areas of the photograph, and is due to residual dye couplers for the magenta dye, which form these stains as they decompose.
The increase in digital photography in the last decade means that many photographs are now printed on photo printers rather than processed in the traditional way. These prints are created using dyes and inks, some of which are not stable and long lasting (see the discussion of colorants elsewhere in this session). Waterproof pigment-based inks are more stable than dye-based water sensitive inks, but they usually have a smaller range of color. Many types of paper supports are also used, including laser/copying paper, general purpose inkjet paper, fine art papers, and coated inkjet papers (which have a special coating to help them receive the inks).
Ultimately, using the right combination of paper, printer, and ink is most crucial to digital print longevity. Wilhelm Imaging Research (founded by Henry Wilhelm, an expert in the field of color photographic materials) has tested many papers, inks, and printers on the market today. In addition to providing guidance on the life expectancies of various digital prints, these tests have shown that using third party inks and paper will not provide the same durability as using ink and paper recommended by the printer manufacturer. See "Creating Long-Lasting Inkjet Prints" by Monique Fischer for more detailed information.