Posted on 10/17/2006 2:04:35 PM PDT by blam
Study Reveals Why Blue Frescoes Fade
Rossella Lorenzi, Discovery News
Keeping Blue Bright
Oct. 13, 2006 — Medieval and Renaissance Madonnas will no longer risk their vibrant blue mantels turning into yellowish grey robes, according to U.S. researchers who have discovered why natural ultramarine blue sometimes fades in frescoes.
Known as "ultramarine sickness," the irreversible form of discoloration has been observed in frescoes at the Church of Saint Augustine in San Gimigniano, near Siena, and in the Basilica of Assisi.
"Our studies explain for the first time the process of fading in ultramarines and may lead to the design of proper art conservation treatments and the development of more-permanent pigments," Alexej Jerschow, an assistant professor of chemistry at NYU, wrote in the journal Inorganic Chemistry, with Eleonora Del Federico, an associate professor of chemistry at the Pratt Institute, and colleagues.
Derived from the semi-precious stone lapis lazuli (literally "blue stone"), ultramarine blue has been one of the most valued pigments by European painters since the late 13th century.
Since the process to extract the pigment from the mineral was very expensive and complicated, ultramarine — from the Latin ultramarinus, meaning "from beyond the sea" — was more precious than gold.
The use of this color was usually reserved to artworks of great importance, such as the funeral mask of Tutankhamen. The pigment found its most extensive use in 14th and 15th century Italian paintings, and was often reserved for the robes and mantels of Christ and the Virgin Mary.
Ultramarine blue was also used by Michelangelo for the skies of the Last Judgment in the Sistine Chapel in Rome.
To discover the mechanism behind ultramarine fading, Jerschow and Del Federico produced frescoes with the pigment and stored them in a chamber at 85 percent relative humidity for two weeks. After that time, the rich and vibrant blue faded to a yellowish grey.
The researchers examined the simulated and degraded fresco samples with nuclear magnetic resonance (NMR), a technology that shows the structure of molecules.
The test showed that the ultramarine's color-forming molecule, or "chromophore," is composed of three sulfur atoms plus one electron. Under normal conditions, the ultramarine chromophore remains trapped in a cage of aluminum and silicon atoms.
But the framework breaks apart if the fresco is exposed to humidity or acids.
"There is a release of the color forming molecules, upon which they are oxidized to form compounds with little or slightly yellowish color," Jerschow told Discovery News.
The research also shed new light on Michelangelo's work in the Sistine Chapel.
"During the restoration of the Last Judgment, restorers found an extra layer of ultramarine, meaning that the artist reinforced the color... This means that Michelangelo might have experienced some ultramarine fading when painting with humid weather," Del Federico told Discovery News.
According to Mauro Bacci, head of research in structure of matter and spectroscopy at the Italian National Research Council in Florence, the study adds our knowledge of pigments in artworks, but should not cause alarm among preservationists.
"We should not worry too much about ultramarine sickness," Bacci told Discovery News. "It is unlikely that a fresco would experience the same lab conditions of the test."
GGG Ping.
I've been losing sleep over this question for years. Deep depression and anxiety have me on suicide watch.
Yeah, well perhaps.
What I really want to know is why do birds suddenly appear, everytime you are near?
One of the few (and for several centuries, the only) source of lapis lazuli was Afghanistan...One more reason to keep it out of the hands of the Taliban.
And while you're at it, find out who put the ram in the rama lama ding dong.
I do not believe this. It is more likely impurities and nonstochiometric proportions in the natural material.
Ultramarine Blue has been synthesized for years and is known for its remarkable stability. The vinyl liner in my swimming pool had been exposed to oxygen, ozone, chlorine, and of course water and its vapor for two decades and has scarcely faded at all.
Ultramarine Blue is used in so many common thermoplastics exposed to hostile conditions, such as laundry detergent and bleach bottles, that there have to be other mechanisms involved here.
So.
Where's my grant money?? :-)
Just like me, they want to be close to you?
I could think of better things to do with that study money. Like buy a party boat, a Harley, build an additon on my house....
I thought ultramarine sickness was a severe form of sea sickness.
Thought you might like a ping!
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Fascinating hypothesis. Be sure & put on your grant application that extensive field research by an assistant will also be required at San Gimignano, and additional funds to provide a villa,transportation,& full living expenses sufficient to support me there in a manner to which I have become accustomed must be included in your stipend.
art ping?
Your pool is ultramarine blue? I would have said that pools appear to be cobalt blue.
The pigment used in the vinyl liners is ultramarine blue. It is chosen for its fade resistance and resistance to oxidation.
Organic pigments such as Monastral (Phthalocyanine) Blue do not do well in that environment.
Wikipedia says
"Artificial, like natural, ultramarine has a magnificent blue colour, which is not affected by light nor by contact with oil or lime as used in painting."
However it does say it is bleached by HCl. But it has survived twenty years in my pool, which never runs below 1.5 PPM Chlorine.
A pigment manufacturer's site says:
"Ultramarine pigments are inorganic pigments. They have a low level of toxicity and are non-irritating and non-sensitizing. They are used where colorants possessing excellent heat stability, light fastness and solvent resistance are required. "
Having ground natural lapis lazuli, it gives off a sulfur odor, not usually detected in the synthetic pigment, so I suspect that the natural pigment used long ago and ground from the stone often has sulfur surpluses in its natural occurrance. Iron Pyrite often is found in natural lapis, and in jewelry produces a beautiful "Starry Night" appearance, with the golden flecks on the deep blue. But if pyrite was present when the Old Masters ground the pigment, then all bets are off regarding hydrolytic stability.
I regret those positions have been filled by a couple of pool ornaments I know..... :-)
DARN! Couldn't I nail you for discriminatory hiring practices or nepotism or something? You have made a comparative judgement on my pool ornamentation skills without any evidence!
Very interesting. Yhanks for posting
-PJ
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