That is neat. I had no idea that microdots had a history before they were used by spies. I thought that grainless film, where the photosensitive component is at the molecular level, wasn't developed until 1930. But the old collodion process used was grainless, although really slow, as in light-insensitive. As a process for making original photographs it was barely usable, but this is using it to make prints, for which light sensitivity is no problem.

This has steampunk potential.