Early photographic negatives:  Before film, photographers used glass plates coated with a light-sensitive emulsion to capture images.
 * Two main types:
   * Wet plate collodion: Used from the 1850s-1880s. Required immediate processing after exposure, leading to uneven coatings and thick glass.
   * Dry plate gelatin: Invented in the 1870s, these were more convenient, pre-coated, and produced sharper images on thinner glass.