In my first post on red chalk, I wrote that red chalk was limited to marks made by readers in medieval manuscripts. Since then I’ve changed my ideas on this because of a medieval manuscript that passed through Sotheby’s London on 8 July 2014, lot 49. The manuscript is known as the Northumberland Bible, after its owners, the Dukes of Northumberland. According to the Sotheby’s cataloguer, it was probably made in the north of England, and dates to circa 1250-60. Just below is a detail of a pen-flourished initial and in the margins one can see the bounding lines in either red crayon or red chalk. It might well be crayon as the lines don’t seem to have budged. The folios aren’t numbered, but it’s the third from the last illustration or second illustration of an opening in the Sotheby’s entry. Sotheby’s includes other images from the bible with evident red crayon/chalk, but this seemed the clearest. There is no mention in the entry of bounding lines or ruling, but this is maybe their convention. (A brief look at other lots in the sale made no mention of ruling or the materials used for the lines.)
The British Library have a very useful illustrated glossaries section for the terms used to describe illuminated manuscripts. It’s based on a book by Michelle P. Brown, which was published jointly by the British Library and the Getty Museum in 1994. Links to the chalk and crayon entries may be accessed by clicking on the words. I’ve also pasted the entry definitions here:
Chiefly composed of calcium carbonate, chalk was used for a variety of purposes in manuscript production: as a POUNCE when preparing the PARCHMENT surface; as a component of GESSO or another GROUND; as a white PIGMENT; as an alkaline component in pigments (serving to modify the colour of certain organic pigments, such as folium, and to lighten and increase the opacity of others); or as a drawing medium.
Crayon, to me, implies more a fabricated medium than a natural one, but I love the term solidified pigment because it leaves the origin vague. I also think of crayon as more lustrous, and less friable, than chalk.