Collotype is a photo mechanical process where you create a plate from gelatin (with dichromate) on a piece of glass. It creates true continuous tone, and it can pick up very subtle details and nuances of the originals.
This was very popular process in the early 1900s before the offset printing become more dominant in printing industry. Berido is quite often commissioned by Japanese government to create copies of old paintings.
This is from a show we had last year, but you can see more images and read a little bit more about it here:
Again, we will post the video clip of the entire process as soon as we find out where to place it on web...