Many of the beautiful medieval manuscripts we can still see today have benefited from the services and skill of a "Rubricator" - with "Rubrisher" being an alternative form. The word derives from the Latin verb "rubricare" which means "to colour red" and that is a simple and accurate description of the task. A rubricator added red ink to important sections of the manuscript, often including headings, and, in ecclesiastical documents, emphasising actions rather than words. Particular canonical or saints' days could also be treated in this way.

A recipe for the creation of the red ink is to be found in the writings of Theophilus Presbyter, who provided instructions on many medieval crafts. It was not an expensive process, though a long-winded one, and involves such substances as lead and urine.

Other colours were also used sometimes, but red was the most common.

With the advent of the Printing Press, the creation and embellishment of manuscripts diminished, but even though one would be unlikely to meet a "Rubricator" nowadays, the practice has been immortalised through the phrase "Red Letter Day".

More Info: en.wikipedia.org