Guild, focused on producing copies of books.
Process of relatively cheap mass-production of copies is kept secret and consists of making a "light-page" - semi-transparent mask of original text - and "dark-page" - a casted shadow on pigment-soaked sheet of paper. After sun-bleaching to shape of original text, it's chemically fixed to prevent further pigment degradation.
(One of the steps of creation of a light-page, firming and drying of transparent material.)
(Making of a light-page of a light-page - cheaper and less readable mask. Dark-pages made from the second layer will be less contrast and a lot cheaper due to passive multiplication of means of production).
(Fixed crude dark-page ready for binding into a book)
(First-copy book ready for distribution, note the overall quality of binding, paper and text)