Black-and-white photographic prints are found in most museums, art galleries and archives. There are many kinds, distinguished from each other by format, image tone, surface gloss and texture. The following remarks are concerned principally with prints in which the image-forming substance consists of microscopic particles of silver. With the exception of pictures dating from the beginning of photography (the so-called salted paper prints from the late-1830s to the mid-1860s), the image silver is embedded in a thin layer that may consist of albumen, collodion, or gelatin, the latter being used almost exclusively for the past 100 years.