Use of yellow pigments
Artists' Materials
Lead-tin yellow is the only yellow pigment used for the images painted within the historiated initials, where it is also employed for highlights over green leaves and mixed with azurite to provide green.
In the letter shapes of the initials themselves and in the border ornamentation, however, lead-tin yellow is substituted on some folios by a lead oxide or by a yellow dye, which in most cases are also mixed with azurite to provide green. These differences suggest that the letter shapes and borders were completed by assistants, while the main artists painted only the images within the initials and the large figures or heads occasionally found in the borders.
Ornamental initials (Ordinary of the Mass)
These are among the twenty-seven ornamental initials that feature occasional caricature-like heads sprouting from the foliage (hotspot 1). Initials of this type are found in only two bifolios (fols. 131-132 and fols. 273-274). They were most likely painted by Bartolomeo di Fruosino whose only recorded payment for work on the Missal specifies the provision of twenty-seven illuminations.