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When Acrylic Paints Get A Spa Day

Andy Warhol's acrylic portrait of Brooke Hayward needed the surfactant that had exited the painting to be cleaned off. Conservation scientists used surface imaging technology to monitor the cleaning process. Credit: MOLAB.

When acrylic paint was introduced in the late 1940s it was a boon for artists with a penchant for instant gratification: Acrylics dry within hours, compared to the weeks and sometimes months it takes for oil paint to completely harden.

But few things in life are perfect, and acrylic paint is no exception. In order to keep pigments stable in the acrylic polymer base, paint makers had to include additives called surfactants. Unfortunately, after a few years or decades, the surfactants get itchy feet and rise out of the paint to the surface of the artwork.

Once there, these surfactants can leave a white film on priceless paintings and they can also be sticky, attracting dirt and grime to the artwork.

In this week’s C&EN, my colleague Celia Arnaud digs deep in to acrylic paint chemistry and talks with conservation scientists about what they do to remedy the problem of wandering surfactant.

Unfortunately, many existing solvents that might be used to clean off the surface of acrylic artworks tend to make the paint swell… This makes museum staff nervous because it’s not clear what long term consequence come from this swelling. Another problem is that solvents that don’t cause acrylic paints to swell aren’t typically good cleaners.

That’s why researchers at the Tate Galleries in London, the Getty Conservation Institute in LA and the DOW chemical company have teamed up to try and find a solvent that cleans but does not swell acrylic paint. At the same time researchers at the University of Delaware are working with Golden Artist Colors, a paint company, to work out good cleaning conditions for acrylic paintings.

If these researchers hit paydirt, acrylic paintings around the world will finally get that facial treatment they’ve all been needing.

Oldest Paint-Making Workshop Dates Back 100,000 Years

An ancient abalone shell used for paint making and storage. Credit: Science/AAAS.

When early humans wanted to paint their bodies, cave walls and anything else for that matter, they used ochre, the red and yellow pigments found in earth and rock.

Today archeologists are reporting the discovery of a 100,000 year-old ochre-making workshop—the oldest to date–in the Blombos cave along the Cape coast of South Africa.

This pushes back the date–by nearly a factor of two—for when early humans produced and stored chemical products such as paint. The next oldest evidence of a workshop dates from 60,000 years ago.

The discovery shows that 100,000-year-old humans “had an elementary knowledge of chemistry and the ability for long-term planning,” note the authors of the Science

paper (DOI: 10.1126/science.1211535), which includes Norway’s Christopher Hensilwood.

It’s pretty of amazing to think that a group of Middle Stone Age humans had a paint factory in operation.

Apparently the ancient workers first ground the ochre pigments (which are iron oxides and hydroxides) out of rock. Then they heated up animal bones to extract fat and marrow which was used as a binder for the ochre pigments. The early humans also added a bit of charcoal to the mix.

Then the paint was stored in abalone shells. Normally there’s a little air hole found in such shells but the ancient workers blocked the hole so that the paint would last longer. Pretty smart for a caveman (or cavewoman).

Location, location, location. The Blombos cave along South Africa's Cape coast. Credit: Science/AAAS.

Incidentally, up on the embargoed Science

media site, where journalists can download photos of the pigment-making artifacts, there’s also sequence of amazing shots of the coastal workshop cave.

I think it’s pretty clear that this workshop discovery also reveals that ancient humans were early adopters of the real estate truism: location, location, location.

Mercury In Platinum Prints Makes Things Sepia–Or Does It?

Experts have long thought the warm, brownish sepia look comes from mercury bichloride added in the development process, but research shows this is not necessarily true. Credit: Wikimedia Commons.

Around 1889, Gertrude Käsebier, a 37-year-old, unhappily married mother of three, decided to go to art school.

A decade later, around 1900, Käsebier’s photo studio in New York City was so successful that her platinum print portraits were “the thing to have,” in turn-of-the-century socialite circles, says Tram M. Vo, an independent conservator who has been collaborating with Dusan Stulik at the Getty Conservation Institute.

“At the time, photographers charged about $12 for 12 prints,” Vo says. “Käsebier charged people $25 just to sit for a photograph and $5 for a single print.”

There’s not a lot known about Käsebier’s techniques in the dark room because she didn’t leave many notes behind. So Vo is trying to learn about her methods using an analytical technique called X-ray fluorescence spectrometry (XRF). Conservation scientists use XRF to get a list of the chemical elements present in an artwork using X-rays—all without touching or destroying the artwork.

In particular, Vo wants to learn more about the so-called sepia look in many of Käsebier’s prints. Sepia is the word used to describe when black and white photographs have a brownish tint that gives the shots a warm feeling.

In today’s digital world, giving a photo a sepia look is just a Photoshop click away. But when Käsebier wanted to give her platinum prints the sepia look she had to use dark room chemistry.
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Keeping Visitors Out To Keep Cave Paintings Safe

Guest post from Carmen Drahl, a C&EN’s Associate Editor and Haystack blogger.

Overview of the best preserved area of the famous Polychrome Chamber in Altamira Cave. At the end are members of the research team and micro-environmental monitoring station. © MNCN-CSIS, Spain

Growing up, I spent every summer in northern Spain, living in my grandmother’s Oviedo flat and wandering the city and surrounding villages with distant cousins. One of my greatest regrets is never having taken the 3 hour drive to what my grandma called “las Cuevas de Altamira”, the storied caves and UNESCO World Heritage Site that house some of the world’s most striking examples of Paleolithic art.

The caves have been closed to visitors on and off since their discovery in the late 1870s. But they’ve been shuttered indefinitely since 2002, because microbial colonies encroached on the priceless scenes of bison and deer on the stone ceilings. Government officials in Cantabria, the Spanish autonomous community where the cave is situated, would like to reopen Altamira to tourists. Today, in a policy forum in the journal Science (DOI:10.1126/science.1206788), researchers led by Cesareo Saiz-Jimenez from the Spanish Council for Scientific Research (CSIC), argue that would be a bad idea. The team, which has been dealing with the microscopic invaders firsthand, says that letting visitors back into the cave’s fragile ecosystem would quickly undo any good that the closure has done and could cause irreparable damage. Continue reading →

Conserving Mosaics: A Nod To The Chemistry Nobel Prize

When blogger David Bradley posted this lovely image of a Moorish mosaic, I knew I had to learn more about how tile art is conserved.

In honor of today’s Nobel Prize in chemistry to Dan Shechtman for the discovery of quasicrystals, I thought I’d write a little post on the world of mosaic art conservation.

Bear with me–there is a connection.

(This is precisely what I said when Paula Artal-Isbrand, a mosaics conservator at the Worcester Art Museum, answered the phone. Luckily, she didn’t deem me a random freak and then hang up.)

OK. So back to the Nobel Prize. Quasicrystals are regular patterns of atoms that never repeat themselves, much “like the fascinating mosaics of the Arabic world,” noted the prize’s press release.

This got me thinking–and blogger David Bradley too—because moments later he tweeted the perfect Moorish mosaic example you see here. And I knew I had to learn a bit more about mosaic art conservation and restoration.
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Using A Digital Light Projector To Restore Mark Rothko Paintings

Different versions of the same painting. Left: the Rothko painting in its faded form. Middle: The ektachrome photo that had turned too red with time. Right: The painting color-corrected back to 1963. (Apologies for the distorted shot. I was sitting off-center from the PPT projection.)

One of the coolest talks I saw at the ICOM-CC conference in Lisbon last week came from Jens Stenger, a conservation scientist at the Harvard Art Museums in Boston. He had the tricky task of figuring out what to do about five paintings by Mark Rothko in the museum’s collection that were so damaged from sunlight exposure that crimson paint on the canvas had turned to blue.

If just a tiny corner of the paintings were light damaged, museum staff might have considered retouching the artwork with a little paint. But a massive fraction of the massive panels were seriously light-damaged.

And these days the trend in art conservation is to minimize interventions on art, especially contemporary art. So a team of curators, conservators and scientists decided that, “repainting was NOT the way to go,” Stenger said.

But everyone thought museum visitors would want to know how the artwork had looked before the light damage. So what to do?

The solution Stenger came up with is pretty cool: Figure out the exact coloration of the originals. Display the artwork as is, but set up a digital light projector that can cast an image on to the canvases. This projected image temporarily makes the paintings appear as they did when Rothko finished them in 1963. Switch off the projector and the paintings are returned to their current-day states. It’s effectively restoration with an undo button. (And as an aside, the amount of light delivered by the projector is not sufficient to continue to harm the painting.)
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Conserving Contemporary Art… And Your Favorite Mix-Tape

This light artwork involves a lot of electronic toy dogs suspended from plastic bags. This complex installation was made by Francisco Rocha.

I spent most of today learning about what museum scientists and conservators are doing to keep contemporary art in tip-top shape. (This whole week I’m at ICOM-CC, the huge art conservation science conference currently taking place in Lisbon.)

These folks who are developing life-extension treatments for some pretty quirky art and artifacts. I’m talking about gigantic chandeliers made from hundreds of illuminated plastic bags suspended from the ceiling, each bag containing a little electronic toy dog that barks and moves its legs. Gotta love it.

Or they’re working on sculptures made from random objects covered in aluminum paint that are now degrading beneath the metal veneer. Or Nazi typewriters found at bombed Gestapo headquarters. Continue reading →

In Lisbon, Cultural Heritage Science’s Biggest Conference Gets Going

It's not San Francisco folks, it's lovely Lisbon... Credit: Wikimedia commons.

I’ve just arrived in Lisbon, Portugal, along with 900 other delegates interested in the conservation of art and artifacts, for the International Council of Museum’s Committee for Conservation (ICOM-CC) conference.

The mega meeting happens every three years and this time it’s taking place at a conference center in the shadow of the Ponte 25 de Abril, a bridge so reminiscent of San Francisco’s Golden Gate Bridge that I almost got a craving for sour dough. (That’s before I renewed my love affair with pastel de nata, Portugal’s joyous custard pastries.)

The menu for this year’s conference looks so good, I’m not sure whether it is physically possible to take in all the great talks that are scheduled.

Just this afternoon I’m going to learn about conserving wall paintings from Guatemala to India. There’s also a session about the trend among natural history museums to transfer animals (such as sharks) that are currently preserved in formaldehyde or ethanol in to other preservation solutions.

(The problem with formaldehyde is that it’s carcinogenic for museum staff, and DNA in the samples is compromised, thus thwarting the new trend of sequencing the genome of such artifact animals. The problem with ethanol is that long term storage in the alcohol can bleach color from animal samples and mess with their skin texture.)

I don’t want to miss out on the talks about analytical technologies used for auntheticating the origin of ancient photographs, nor how to detect microbial contamination in paper-based cultural heritage–even before any damage is done. And there’s also a whole section on environmentally sustainable conservation, which I touched upon in a previous post.

Stay tuned this week for more conference goodies from Lisbon. Até logo!

Greening Up Conservation Science

My pedestrian Photoshop attempt to give an Egyptian sculpture a greener feel. With apologies to Amenhotep III and thanks to Wikimedia Commons.

Cultural heritage is important so valuable art and artifacts should be protected at any cost, right?

Not so, says May Cassar, the director of the Center for Sustainable Heritage at University College London.

Most museum, galleries and archives take it as a given that air conditioning and pollution filtration are a must for keeping valuable collections in comfortable living conditions, she says.

“But air conditioning and particularly pollution filtration come at a very high cost–not only to institutional budgets but also from an environmental point of view” because fossil fuels are consumed to drive these systems, Cassar explains. “To me it is a double standard to damage the environment outside but protect the environment inside for collections.”

She’s trying to encourage people in cultural conservation careers to consider the environment outside–and not just around valuable collections.

So for example, Cassar advocates that museums in temperate climates–such as the UK–accept some minor risks to collections if there is a possible gain for the environment. For example, a museum might normally use air conditioning to keep humidity in between 50-60%. If the building’s internal humidity would normally only ever range from 40-65%, reaching the outer extremes only rarely, it could be fine for the museum to eschew humidity control without substantially increasing risk to the collection, she says.

Of course, it’s true that some museums don’t have the luxury of a temperate climate… Consider the soul-destroying humidity of Washington DC’s summer months (I barely survived two of them), or the corrosion potential from the high salt concentrations found in the air around ocean-side museums, or the problem New York City’s sooty air pollution raises for valuable collections.

But there may be other ways for museum, archive and gallery staff to go green.
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Dating Silk With Some Fluffy (But Good) Science

Just a little fluff can reveal the age of silk artifacts, such as the age of this Egyptian textile from 900 A.D. Courtesy: The Textile Museum

Scientists at the Smithsonian have come up with a new way to figure out the age of ancient silk artifacts, such as flags, clothing and tapestries, using just a bit of fluff that’s fallen off the valuable textiles.

The only other scientific way to date silk is by carbon-14 dating, which requires about 100 times more sample than the new technique. (There’s another out-dated “stress-strain measurement” test, which as the name suggests, can put precious silk artifacts through some major mechanical procedures to do the dating. Sounds like just the perfect technique for getting on a textile curator’s black list.)

Anyway, the new technique monitors a component of silk called aspartic acid. Silk is essentially a bunch of intertwined proteins extruded from a silk worm, and aspartic acid is found within these proteins.

Aspartic acid can exist in two forms, the L- and D- forms, which have the same chemical formula but are mirror images of each other. When a silk worm extrudes the silk protein, the aspartic acid is only in the L-form, but over time it transforms into the D-form.
Continue reading →

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