The rapid growth of computers during the past decade has introduced new ways of producing color prints. Images can now be converted to digital files—either by scanning traditional photographic prints or, as mentioned above, by recording them with a digital camera. These files can be sent to a home printer to produce acceptable color prints. The majority of photo-quality printers use inkjet technology, in which very small droplets of ink are deposited onto paper. Inkjet prints vary widely not only in the composition of the colorants and paper, but also in stability. Inkjet images may be composed of dyes similar to those used in traditional photographic prints, or of pigments, which are the colorants used in paints. In general, pigments tend to be more stable than dyes. Inkjet prints can be made on either uncoated or coated paper, but only coated paper will provide photo-quality prints. Plain, uncoated paper tends to absorb the ink, resulting in a blurred image and loss of color intensity. In high-quality paper, a coating prevents the ink from bleeding into the paper; this results in brighter, more saturated color and greater image detail. Coated papers may closely resemble traditional color print supports. Two main types are available: swellable and porous. In general, acid-free, buffered, and lignin-free paper bases are recommended for long-term storage.
Swellable Paper
As its name implies, the surface of this type of inkjet paper swells in the presence of the moisture in the water-based ink, allowing the colorants to penetrate the top layers. Swellable papers typically have three active layers: a protective top layer, a layer that fixes the ink droplets in place, and, below that, a layer that absorbs additional ink components. The paper base is sandwiched between two polyethylene layers and backed by an anti-curl coating and an antistatic layer. Premium swellable papers contain all of these layers, but less expensive ones may not.2 The polymer coating on swellable papers acts to maximize image brightness by keeping the colorants from spreading, and, to some extent, it protects the image from atmospheric pollutants. Images printed on coated paper may require a significant amount of drying time.
Porous Paper
The surface of porous paper is coated with very small, inert particles, which create numerous minute cavities in which the ink is deposited. These particles prevent the ink from spreading. Porous paper has a higher resistance to moisture and humidity. This paper requires minimal drying time, so the print can be handled immediately without fear of smudging. This type of print has no protective polymer layer; therefore, the colorants are susceptible to attack by atmospheric pollutants, such as ozone and oxides of sulfur and nitrogen, which can be present in the environment in fairly high concentrations. Porous paper is preferred when pigment inks are used.
