Cennini was from the town of Colle di Val d’Elsa in Tuscany, and studied with the Florentine painter Agnolo Gaddi (active 1369, †1398). Cennini’s birth and death dates are unknown, but he married a woman from Citadella, north of Padua, and is documented as working in Padua in the closing years of the 14th century. His art treatise, the Libro dell’Arte is known through three early manuscripts, the earliest being in the Laurentian Library in Florence (Laurenziana, LCCVIII, codex 23), which is dated 1437. The work was first published in 1821 by Giuseppe Tambroni. Attempts have been made to attribute art works to Cennini, but nothing is secure.
This link leads to the Milanesi edition of the Libro dell’Arte, published in 1859 and available through Google Books. Pisa’s Scuola Superiore Normale also has the digitized Libro. The school, part of the Pisa University system, provides a website which has an excellent section on digitized art treatises. This link leads to the start page. Linking to individual books is not possible, as the links are unstable.
Cennini never discusses red chalk or crayon, but he speaks of hematite several times in his Libro dell’Arte. In chapters XV-XVII, he discusses how to make grounds for both parchment and paper, saying, among other things, how the support should be flattened, how the pigments must be well ground, and how to apply the tinting grounds with a soft brush. The chapters are very short; often just a few sentences long. Chapter XVIII discusses how to make a purple ground from hematite and lead white. He calls the color morella and gives an alternate color name, pagonazza. (Porpora, the more recognizable word for purple, appears twice in the Libro.)
Morella is a plant of the nightshade family, whose fruit or berry is a deep purple. It is also the name given to a blue-flowered plant, turnsole in English, which was used to produce a blue to purple dye. According to Treccani, the Italian encyclopedia and dictionary, pagonazza is a variant of paonazzo, as is pavonazza, and refers to a violet color in the peacock’s tail plumage. (I had a look at photos of peacocks and I didn’t see any feathers that looked particularly purple. Maybe the length, before the eye, is a dusty purple. I’ll have to remember to look for this when I next see a live peacock.) For a confirmation of the color purple, Filarete (1400-69) in his Trattato di Architettura, f.181v, says “azurro e rosso fa pagonazzo, o vuoi dire morello.” (Filarete’s treatise is online at SSN Pisa.) One can only imagine how many times pagonazza/o and morella/o were said together, up and down the peninsula, to convey the color.
To make this color purple, Cennini combines ½ ounce of lead white with a fava bean amount of hematite. (The fava bean measure shows he’s on the same wavelength as the cookbook writer, Julia Child, with her pea-sized dots of butter; along with Ada Boni and Elizabeth David, with their walnut measure. Or, at least, I can’t think of one without the others when I read these measures.) He uses two slightly different names for hematite, amatita and amatista, in the Libro. The a at the beginning may be a nice vestige of the Greek word. Ematite is the word used for hematite in current Italian.
Cennini says of the white lead and hematite, “grind them well, as much as you can; because grinding it a lot never hurts, but always enhances it.” In fact, grinding well and grinding long is the leitmotif of the Libro. Whether Cennini had a particularly purple hematite or whether his expert grinding turned the color from its usual red, is something that has to be left open.
Just above is a drawing attributed to Fra Angelico, and is dated to c. 1450. It is at the Boijmans Van Beuningen museum in Rotterdam, and is one from a series of ten miniature drawings figuring the life of Christ, of which the Boijmans has seven (link to the seven here). It is on parchment, unlike most of the existing 15th century metalpoints, which are on paper. The cataloguer describes the color of the ground as red-violet. It’s probably more red than Cennini’s ground color, but it would be interesting to read if they’ve examined the color in the lab. Two of the drawings in the series, the Lamentation, and Christ Among the Doctors appear to be on a slightly different color of prepared parchment. Again, I haven’t read about this, but it could be a different batch of preparation than the other five, they could have been photographed on more than one day (!), or maybe they were subjected to more light. In any case, it is very hard for me to take my eyes off the images of these drawings. I now have three on my desktop.
Note of 25 July: The Boijmans drawing may well be pagonazza in color. Serpone & Company, a Naples firm specializing in religious vestments, sells a short cape for bishops, which is similar in color and which they call paonazza.
Other references to hematite in the Libro include the use of a smoothed piece of hematite to burnish gold, and as a pigment for painting. Hematite-rich materials such as bol and sinopia are also discussed, but not in relation to drawings on paper or parchment.