The highly burnished gold leaf in the backgrounds of all miniatures and historiated initials was laid over a black-coloured bole which contains calcium and copper. Visible through small losses in the gold leaf, the black bole reveals the main artists’ awareness of the subtle changes in the tonality of the gold leaf produced by varying the colour of its base. In the smaller, ornamental initials, which were painted by assistants, the gold leaf is laid over a white bole, commonly found in 13th-century Parisian manuscripts. Exceptionally rare, black bole was used only in very few deluxe manuscripts, including royal commissions. It appears in the full-page miniatures which one of the artist involved in this Psalter-Hours (Hand C) contributed to the St Louis Psalter (Paris, BnF, MS lat. 10525, fols. 25v-28).
