The selection of fragments contained many of those pigments already noted in the extensive analytical work conducted elsewhere in Europe7,8,9,10,11,12,13,14, such as azurite, red lead, vermilion, orpiment, and copper-based greens. Even though these fragment pages might appear rather simple in terms of their colour scheme, the analysis has shown a greater variation and complexity than first meets the eye. This observation will be further elaborated below where findings are listed by colour. A summary of the findings can be found in Table 2. Further images and XRF maps can be found in Supplementary information 2 (SI2), and 3 (SI3).
Table 2 Summary of identified colourants and inks based on results from FTIR, Raman, HSI, FORS and XRF Full size table
Blue
All blues, except one, were identified as azurite by HSI (absorption max 640 nm) and FTIR (a strong doublet at 4380 and 4244 cm−1, which can be attributed to both the combination of ν + δ (OH) and the overtone 3ν3. This doublet partially overlaps with the methylenic C–H stretching and bending combination from lipidic binders), and is further corroborated by the presence of copper in the XRF analysis12,22. Azurite is a basic copper (II)-carbonate: 2 CuCO 3 ·Cu(OH) 2 forming bright blue crystals. The pigment can be prepared either from naturally occurring minerals or produced synthetically. The presence of particular impurities can arguably be used to attribute origin and identify leaves that come from the same workshop23. The azurites of the pages of the investigated selection show a variation in impurities, which could indicate different geological sources or different grades of purification. They showed the presence of barium, iron, zinc, arsenic, manganese and bismuth in XRF analysis with notable variability between the various fragments (Fig. 3, Table 2). The combination of impurities can thus confirm the likeness or not of the different fragments or various leaves of the same fragment. The presence of impurities in azurite has been noted in other analyses. For example, iron has been observed in 11th-century French manuscripts and zinc, arsenic, and barium in one 16th-century Flemish Book of Hours24. Barium, arsenic, zirconium, and bismuth were detected in two Italian manuscripts from the 13th and 15th centuries while antimony and silver were found in a 15th-century Spanish manuscript in synchrotron XRF analysis23.
Fig. 3: Micrographs of azurite blues and their XRF spectra. Micrographs (a) of azurite blues of four fragments and XRF spectra of the blue areas shown in SI2 (b). Note variability in minor components such as manganese, barium, zinc, arsenic, and bismuth. Full size image
Azurites are described as rendering varied colour hues depending on grain size16. The azurite blues of the selection show a variation of finely ground particles hardly discernible at ×80 magnification (Fr 4602 and Fr 10156) to a coarser grain size of ~20–40 µm in Fr 6638 and Fr 3814.
The exception to the use of azurite was the blue writing in the 12th-century calendar fragment Fr 25621, which was identified as ultramarine with HSI, (absorption max 600 nm)12, and Raman spectroscopy (peak located at 545 cm−1 attributed to ʋ sym (S 3 −)25 (Fig. 4). Raman band at 1316 cm−1 indicates the possible presence of natural mineral such as diopside (CaMgSi 2 O 6 ), commonly associated with lapis lazuli in nature26, and suggests that transition metal dopants in the diopside may be responsible for the Raman features, likely the result of fluorescence with vibronic coupling27. Ultramarine is not an uncommon pigment used for manuscript colours. The source of natural ultramarine is the rock lapis lazuli, which contains a mixture of the minerals calcite, pyrite, and lazurite. The latter is a complex sulfur-containing sodium aluminium silicate, Na 6 Ca 2 (Al 6 Si 6 O 24 )S 2, which is the actual colouring agent of ultramarine28. This pigment has been found in many manuscript illuminations but was not so commonly used as ink to write text. However, blue text is quite often encountered in calendars. While the colour red was the most common one used to designate the most important saints29, blue was also used, at least in twelfth- and thirteenth-century manuscripts.
Fig. 4: Photographs, Raman and HSI mean spectra of the blue ink of Fr 25621. Fragment 25621 (a, detail), a 12th-century calendar with blue text identified as ultramarine. b Microscopic view (×80 magnification), c Raman spectrum (exc.785) and d HSI mean spectrum (blue line, absorption max. 600 nm) with standard deviation (blue area) and ultramarine reference spectra (pure, in powder, dotted black line). Full size image
Natural ultramarine is described as a precious pigment. The preciousness of ultramarine stems from the scarcity of known mineral sources for the lapis lazuli rock from which the pigment is obtained. Probable places of origin are Tajikistan, Pakistan, and Afghanistan26. It has been observed that there was a varying geographical and chronological use of different blues in the early medieval period, as azurite is more commonly found in Carolingian manuscripts, and ultramarine appears more often in Ottonian manuscripts and in early medieval England. In England, the use of azurite was not common until the 12th century9,10. The calendar fragment, Fr 25621, was produced in the late 12th century. The only Nordic saints in the original hand are Olav and Canute, which points to the calendar originating in the diocese of Linköping or possibly Denmark. Certainly, the manuscript was later adapted for use in the diocese of Linköping. As for ultramarine’s other applications in the Swedish context, the use of this pigment in contemporary Swedish wall paintings was not very common; it was only found in 10 out of the 70 analysed medieval church murals30. The blue text of Fr 25621 is also associated with the presence of lead, with lead white being confirmed by external reflectance FTIR (SI4_1), for the characteristic combination bands (CO 3 −2) at ca.1730 and 2400 cm−1 22.
Red
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