Fifty shades of blue: lapis lazuli
The incredible beauty of the Sistine Chapel with its Last Judgmen, whose execution is a well-known story, hides an even more peculiar event: the history of the lapis lazuli.
If there was a hierarchy of colors, the lapis lazuli would be the King of the Blues: during the past centuries it was so expensive that it was often falsified or used in small quantities. Moreover, it usually had to be mixed with other cheaper pigments. The cause of the high cost lied into the difficulty of finding the raw material. The mineral, in fact, was imported following a well-defined trade route: the way of lapis lazuli.
Lapis lazuli is the common name of the lazurite mineral (from the Persian word "lazhward", that means blue). It is often found in association with other minerals (such as pyrite, phlogopite, calcite, pyroxene and various silicates) and, consequently, it has a complex chemical formula which can be synthesized as: (Na, Ca)8 [Al6 Si6 O24] (Sn -, S2-, SO4 2-, Cl-) 1-2. Lazurite can be easily found along with Hauyna mineral, which has the same chemical formula and it differs only for the dominant sulfate.
The lazurite in the artwork is easily recognizable by the richness of its color. Among the scientific techniques aimed at its recognition, the XRD, the optical microscopy SEM, the microprobe and the Raman spectroscopy (What is Raman? Click here for more information) are the most common used.
In ancient times, , the only sources of the raw material were probably the quarries of Pamir and the Afghan of Sar-e-Sang. From this place, the aforementioned "Route of lapis lazuli" began.
In a 2006 Ballirano and Maras (Sapienza, University of Rome) worked on fragments of the Lapis Lazuli of the Sistine suggesting a hypothesis of provenance for the lapis lazuli used by Michelangelo (reference in the bibliography).
Before being used as pigment, the lazurite had to be cleaned from impurity, especially pyrite. This process increased the cost of the pigment. On the other hand, this pigment is one of the most stable over the time. His stability is due to the complex mineralogy of lazurite that is part of the class of silicates (subclass tectosilicates, group of feldspatoids) that makes it resistant to the most aggressive chemical attacks.
In the case of Michelangelo's Judgment, moreover, the fresco technique has still enhanced its color and brightness, something that in oil techniques or a tempera does not always happen. The issue about the cleaning of this work of art deserves a separate post. Anyway, everything that has been deposited on the surface has practically not altered the color of the lapis lazuli. Just in some areas of the fresco it was possible to identify an alteration called "Ultramarine disease". This alteration, however, is still partly unexplained as it is not certain whether it is related to an ancient cleaning or if there were no lapis lazuli in those areas of the fresco.
Today the lapis lazuli is considered an ornamental stone, a jewel that still maintains very high prices. Science, as one could expect, has succeeded in synthesizing an artificial lapis lazuli, which preserves the optical characteristics of the original one and has a reduced commercial value. However, this would hardly be able to give the expressive intensity as the natural lapis lazuli does in the Last Judgment as Michelangelo..
If there was a hierarchy of colors, the lapis lazuli would be the King of the Blues: during the past centuries it was so expensive that it was often falsified or used in small quantities. Moreover, it usually had to be mixed with other cheaper pigments. The cause of the high cost lied into the difficulty of finding the raw material. The mineral, in fact, was imported following a well-defined trade route: the way of lapis lazuli.
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| The Last Judgment (Sistine Chapel) by Michelangelo Buonarroti (Source: Wikipedia) |
The lazurite in the artwork is easily recognizable by the richness of its color. Among the scientific techniques aimed at its recognition, the XRD, the optical microscopy SEM, the microprobe and the Raman spectroscopy (What is Raman? Click here for more information) are the most common used.
In ancient times, , the only sources of the raw material were probably the quarries of Pamir and the Afghan of Sar-e-Sang. From this place, the aforementioned "Route of lapis lazuli" began.
In a 2006 Ballirano and Maras (Sapienza, University of Rome) worked on fragments of the Lapis Lazuli of the Sistine suggesting a hypothesis of provenance for the lapis lazuli used by Michelangelo (reference in the bibliography).
Before being used as pigment, the lazurite had to be cleaned from impurity, especially pyrite. This process increased the cost of the pigment. On the other hand, this pigment is one of the most stable over the time. His stability is due to the complex mineralogy of lazurite that is part of the class of silicates (subclass tectosilicates, group of feldspatoids) that makes it resistant to the most aggressive chemical attacks.
In the case of Michelangelo's Judgment, moreover, the fresco technique has still enhanced its color and brightness, something that in oil techniques or a tempera does not always happen. The issue about the cleaning of this work of art deserves a separate post. Anyway, everything that has been deposited on the surface has practically not altered the color of the lapis lazuli. Just in some areas of the fresco it was possible to identify an alteration called "Ultramarine disease". This alteration, however, is still partly unexplained as it is not certain whether it is related to an ancient cleaning or if there were no lapis lazuli in those areas of the fresco.
Today the lapis lazuli is considered an ornamental stone, a jewel that still maintains very high prices. Science, as one could expect, has succeeded in synthesizing an artificial lapis lazuli, which preserves the optical characteristics of the original one and has a reduced commercial value. However, this would hardly be able to give the expressive intensity as the natural lapis lazuli does in the Last Judgment as Michelangelo..
Francesca
- P. Ballirano, A. Maras, Mineralogical characterization of the blue pigment of Michelangelo’s fresco “The Last Judgment”, American Mineralogist, Volume 91, pages 997–1005, 2006
- Paolucci, La Cappella Sistina http://www.hoepli.it/libro/la-cappella-sistina/9788895847542.html
- La Cappella Sistina Volume 3: Storia della Creazione, Frederick Hart
- http://www.catalogomultimediale.unina.it/?p=980
- http://rruff.info/Lazurite
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