Invented 140 years ago in 1880s Zurich, Photochrom, a.k.a. Fotochrom, Photochrome or Aäc process, is an old school process for colourizing black-and-white negatives via the direct photographic transfer of a negative onto lithographic printing plates. The process is a photographic variant of chromolithography (color lithography).
Imaginatively selecting & mechanically colouring a black & white photo rather than doing it by hand.
The printer is PhotoGlob & Company of Zurich, the inventors of the process.