Illumination:

After the text had been rubricated, it would be given to a skilled artisan for added illustration.  Not all texts went through this process; there are many manuscripts that exist without any illustration at all.  Texts that were intended to be illustrated, however, would be transcribed with gaps left for the illustrations and illuminated letters.  The text's scribe would generally make notes in the margin or gap of the text indicating what was intended to fill the space; these notes are still occasionally visible through or beside the added illustration.

Artisans adding illustrated initials would often depict human figures and scenes within the openings of the letter.  These letters are sometimes termed historiated initials, and often the scenes depicted "relate directly to the text that the initial begins" (Graham and Clemens 27).  These letters could be extremely decorative and were in nicer texts sometimes done in purple or gold inks, significantly inflating the value of the manuscript.  Artists in training frequently copied illuminated letters and illustrations from the original exemplar, just as the scribe had done. More experienced artisans, however, could freehand the work, though this was not particularly common (Graham and Clemens 27).

The pigments used by the artists exist in a variety of forms, including earth pigments (those that were mined from the earth and used "with little processing"), inorganic pigments (those mined from the earth and greatly processed), synthetic inorganic pigments (pigments created from materials that are not themselves pigments), and organic pigments (those taken from living plants and, occasionally, animals) (Graham and Clemens 27).  The most valuable coloration, however -- gold and silver -- were applied in leaf form, pressed into the page with an adhesive. 

The illustrations in medieval texts could also be discursive or figural, though these are terms present-day scholars apply to manuscripts.  Discursive images are those that are drawn by artists nearly entirely from imagination; figural images, conversely, draw directly from the text and depict very little but what is mentioned in the actual words of the text.