Robert W. Sprague was an British engraver, lithographer and printer. His ink-photo process was a version of collotype.

From the Getty’s Atlas of Analytical Signatures of Photographic Processes... A number of collotype variants were developed and patented since its introduction in the 1860s. They include, among others, Alethetype, Autocopyist, Gelatinotypy, Leimtype, Heliotype, Indotint, Ink-Photo, Lichtdruck, Papyrotype, Photophane, Roto-Collotype, Rye’s, and Sinop. A majority of these differ in technical details that do not have an effect on the final microstructure of the printed image. Even if a typical feature of the printed microstructure is present, such as the more pronounced grain microstructure of the Ink-Photo process, it does not provide the fully reliable visual signatures needed for process identification. The collotype process variants also do not differ in their chemical signatures; the only differences are small but atypical chemical differences in the paper substrate and the stiff oil-based collotype ink. [1]