The platinum printing process was popular in the late 19th century. It used platinum and/or palladium salts instead of silver as the light-sensitive material. These prints are characterized by their ability to reproduce a long scale of tonal values. It is a very permanent image and was highly valued for this reason. Later the process was appreciated more for its aesthetic qualities and became favored among art photographers. It is usually characterized by soft, gray tonalities, but it is possible to change the color of the print during development or by toning the finished print. Platinum prints have a different appearance from silver gelatin or digital prints. All platinum prints have a matte, not glossy surface because the sensitizer is absorbed into the paper rather than sitting on the surface. A platinum print also has a more gradual tonal change from black to white. To the eye, a platinum print will often look softer.