Unusual use of blue pigment found in ancient mummy portraits

Mostly untouched for 100 years, 15 Roman-era Egyptian mummy portraits and panel paintings were literally dusted off by scientists and art conservators from Northwestern University and the Phoebe A. Hearst Museum of Anthropology as they set out to investigate the materials the painters used nearly 2,000 years ago.

What the researchers discovered surprised them, because it was hidden from the naked eye: the ancient artists used the pigment Egyptian blue as material for underdrawings and for modulating color -- a finding never before documented. Because blue has to be manufactured, it typically is reserved for very prominent uses, not hidden under other colors.

"This defies our expectations for how Egyptian blue would be used," said Marc Walton, research associate professor of materials science and engineering at Northwestern and an expert on the color blue. "The discovery changes our understanding of how this particular pigment was used by artists in the second century A.D. I suspect we will start to find unusual uses of this colorant in a lot of different works of art, such as wall paintings and sculpture."

The best Roman-era painters tried to emulate Greek painters, who were considered the masters of the art form. Before the Greek period, Egyptian blue was used everywhere throughout the Mediterranean -- in frescoes, on temples, to depict the night sky, as decoration. But when the Greeks came along, their palette relied almost exclusively on yellow, white, black and red.

"When you look at the Tebtunis portraits we studied, that's all you see, those four colors," Walton said. "But when we started doing our analysis, all of a sudden we started to see strange occurrences of this blue pigment, which luminesces. We concluded that although the painters were trying hard not to show they were using this color, they were definitely using blue."

The study was published this month by Applied Physics A, a journal focused on materials science and processing. The research collaboration is part of the Northwestern University-Art Institute of Chicago Center for Scientific Studies in the Arts (NU-ACCESS), for which Walton is a senior scientist.

"Our findings confirm the distinction between the visual and physical natures of artifacts -- expect the unexpected when you begin to analyze an artwork," said Jane L. Williams, a conservator at the Hearst Museum and a co-author, along with Walton, of the study. "We see how these artists manipulated a small palette of pigments, including this unusual use of Egyptian blue, to create a much broader spectrum of hues."

The researchers studied 11 mummy portraits and four panel painting fragments. The 15 paintings were excavated between December 1899 and April 1900 at the site of Tebtunis (now Umm el-Breigat) in the Fayum region of Egypt. They now are housed in the collections of the Hearst Museum at the University of California, Berkeley.

The fragile mummy portraits are extremely lifelike paintings of specific deceased individuals. Each portrait would be incorporated into the mummy wrappings and placed directly over the person's face, Williams explained.

While working on the conservation treatment of these paintings, Williams had many unanswered questions about their materials and techniques, but without a conservation science division at the Hearst Museum, she had limited means to investigate. Working with NU-ACCESS made a comprehensive technical survey of the paintings possible, Williams said.

Walton and his Northwestern team brought expertise in scientific analysis of cultural heritage materials and some of the latest technology for the non-destructive analysis of artworks to the Hearst Museum. The study quickly revealed some surprises.

The researchers uncovered the unexpected uses of Egyptian blue -- the first man-made pigment, inspired by lapis lazuli, the true blue -- using a routine battery of different analytical techniques, such as X-ray fluorescence and X-ray diffraction. Six of the 15 paintings have the unusual use of blue, the researchers found.

The skilled painters employed blue for underdrawings, to modulate clothes, the shading on clothing and in other not necessarily intuitive uses of Egyptian blue, a pigment used for millennia before these paintings were made.

"We are speculating that the blue has a shiny quality to it, that it glistens a little when the light hits the pigment in certain ways," Walton said. "The artists could be exploiting these other properties of the blue color that might not necessarily be intuitive to us at first glance."

Research on these paintings, which is ongoing, will contribute to the international collaborative study project Ancient Panel Paintings: Examination, Analysis and Research (APPEAR), initiated by the J. Paul Getty Museum. APPEAR aims to create an international digital database to compile historic, technical and scientific information on Roman Egyptian portraits.

"Our collaboration with NU-ACCESS makes it possible for the Hearst Museum to contribute to this project at the level of much larger museums, like the Getty or the British Museum, that have conservation science divisions," Williams said.
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Reference:

EurekAlert. 2015. “Unusual use of blue pigment found in ancient mummy portraits”. EurekAlert. Posted: August 26, 2015. Available online: http://www.eurekalert.org/pub_releases/2015-08/nu-uuo082615.php

New study shows South Africans using milk-based paint 49,000 years ago

An international research team led by the University of Colorado Boulder and the University of Witwatersrand in Johannesburg, South Africa has discovered a milk-and ochre-based paint dating to 49,000 years ago that inhabitants may have used to adorn themselves with or to decorate stone or wooden slabs.

While the use of ochre by early humans dates to at least 250,000 years ago in Europe and Africa, this is the first time a paint containing ochre and milk has ever been found in association with early humans in South Africa, said Paola Villa, a curator at the University of Colorado Museum of Natural History and lead study author. The milk likely was obtained by killing lactating members of the bovid family such as buffalo, eland, kudu and impala, she said.

"Although the use of the paint still remains uncertain, this surprising find establishes the use of milk with ochre well before the introduction of domestic cattle in South Africa," said Villa. "Obtaining milk from a lactating wild bovid also suggests that the people may have attributed a special significance and value to that product."

The powdered paint mixture was found on the edge of a small stone flake in a layer of Sibudu Cave, a rock shelter in northern KwaZulu-Natal, Africa, that was occupied by anatomically modern humans in the Middle Stone Age from roughly 77,000 years ago to about 38,000 years ago, said Villa. While ochre powder production and its use are documented in a number of Middle Stone Age South African sites, there has been no evidence of the use of milk as a chemical binding agent until this discovery, she said.

A paper on the subject was published online June 30 in PLOS ONE. Co-authors were from the Italian Institute of Paleontology in Rome, Italy; the University of Geneva in Switzerland; the University of Pisa in Italy; the University of Monte St. Angelo in Naples, Italy; and the University of Oxford in England. The excavation was directed by Professor Lyn Wadley of the University of Witwatersrand, also a paper co-author.

Cattle were not domesticated in South Africa until 1,000 to 2,000 years ago, said Villa. Wild South African bovids are known to separate from the herd when giving birth and usually attempt to hide their young, a behavior that may have made them easy prey for experienced Middle Stone Age hunters, she said.

The dried paint compound is preserved on the stone flake that may have been used as a mixing implement to combine ochre and milk, or as an applicator, said Villa. The team used several high-tech chemical and elemental analyses to verify the presence of casein, the major protein of milk, on the flake.

At both African and European archaeological sites, scientists have found evidence of ochre—a natural pigment containing iron oxide than can range from yellow and orange to red and brown - dating back 250,000 years. By 125,000 years ago, there is evidence ochre was being ground up to produce a paint powder in South Africa.

It has been proposed the ochre was sometimes combined by ancient Africans with resin or plant gum to use as an adhesive for attaching shafts to stone tools or wooden bone handles, Villa said. It also may have been used to preserve hides and for body paint, she said, noting that a roughly 100,000-year-old ochre-rich compound blended with animal marrow fat was found at the Middle Stone Age site of Blombos Cave in South Africa.

Body painting is widely practiced by the indigenous San people in South Africa, and is depicted in ancient rock art. While there are no ethnographic precedents for mixing ochre with milk as a body paint, the modern Himba people in Namibia mix ochre with butter as a coloring agent for skin, hair and leather clothing, Villa said.
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Reference:

Phys.org. 2015. “New study shows South Africans using milk-based paint 49,000 years ago”. Phys.org. Posted: June 30, 2015. Available online: http://phys.org/news/2015-06-south-africans-milk-based-years.html

Terracotta Army's vibrant make-up was made of ox glue

The 8000 strong warriors of the Terracotta Army in Xi'an, China, are a formidable enough sight today – but imagine if you could see the whites of their eyes and the blood in their cheeks. When the army was buried 2000 years ago the life-size figurines were painted in a variety of bright hues, including green, blue, pink, red, black, white and lilac. Only traces of that colour remain now, after looting, fire, centuries of water damage and exposure to the open air – all of which took their toll on the paint.

Now we know how these vibrant pigments adhered to the brown clay – animal glue made from ox parts. A team from Northwest University and the Museum of Emperor Qin Shihuang's Terracotta Army, Xi'an, made the match by comparing the protein molecules in the original paint with artificially aged model samples daubed with different types of binding media.

Now that the paint's components are better understood, researchers can develop ways to conserve what paint is left, particularly on the thousands of soldiers that still remain to be unearthed.
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References:

Williams, Anna. 2014. “Terracotta Army's vibrant make-up was made of ox glue”. New Scientist. Posted: August 6, 2014. Available online: http://www.newscientist.com/article/dn26007-terracotta-armys-vibrant-makeup-was-made-of-ox-glue.html#.U_z9-ijGprU