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Changes in the chemical composition of paints in the paintings over time on the example of the famous works of van Gogh

 

The facts proving the destruction of chemical pigments

Vincent van Gogh was obsessed with pigments in his paints, and he knew as much or even more about their composition and shortcomings as many of his contemporaries. But the tragic irony is that many of van Gogh's bright red and yellow pigments, which he used in his masterpieces, fade or change color over time.

The destruction of the pigment is certainly not just a problem with van Gogh's work: he used many of the same pigments as other artists of Northern Europe of the late 19th century, such as Pierre-Auguste Renoir or James Ensor. "You can say with confidence that many of the works of that period were probably somehow affected by similar pigment problems," says Ella Hendrix, a senior conservative from the van Gogh Museum in Amsterdam.

However, van Gogh's works have become a kind of lens through which scientists study the degradation of pigment. He was a prolific painter: for 10 years of work as an artist van Gogh created about 1000 paintings. He was also a prolific writer: in letters to family and friends, he discussed in detail the acquired pigments and paints of his recently painted paintings. These written reports are a valuable starting point for scientific research.

As a result, van Gogh's canvases led to numerous discoveries about the decay of constituent particles - or as they are called conservatives "fugitive pigments". This is followed by a series of articles on how the analysis of his paintings helped to highlight the ways of chemical degradation in aging pigments and how this research helps in the methods of display and methods of preserving the unique masterpieces of van Gogh and other works of his time.

 

Red Pigments Red Lake ( Red Lake Pigment) : They Shine Bright, But Fade Quickly

Микрохимическое исследование состава грунта и пигментов     Микрохимическое исследование состава грунта и пигментов

 

Red pigments red lake, used for centuries to decorate illuminated manuscripts and paintings, are extremely prone to fading: organic compounds that make up red pigments, decompose quickly in the presence of light. Van Gogh used several types of this pigment on his canvases, including cochineal, which is extracted from the cochineal insect, and eosin, one of the world's first synthetic organic dyes.

Many of the Reds in van Gogh's works began to disappear "during van Gogh's own life or very soon after," says conservative Ella Hendrix of the van Gogh Museum in Amsterdam. The immediate loss of color was caused by the lack of a form of light control in private homes where his canvases hung.

For example, the pink flowers in "Roses" (shown above) lost their color by 1907, after being hung in his mother's house for 17 years.

Other cases of fading color of his paintings are not always obvious. Consider the landscape of 1888 van Gogh "field with irises near Arles" (shown below). In the letters he called the irises of the picture purple instead of their current bluish hue.

The researchers have since identified the red pigments cochineal and eosin as the cause: the loss of the red shade used to color the colors in purple led to the appearance of blue pigments in the paint.

Identifying long-lost red - like pigments on canvas can be a problem, but conservatives have a few strategies in their hands.

For example, the trick with the identification of eosin is the knowledge that the pigment has four atoms of bromine in its structure, explains Geert van der Snickt from the University of Antwerp. Bromine, an element rarely found in pigments, remains on the canvas as eosin degrades. The researchers, including van der Snick used macroscopic x-ray fluorescence scanning
spectroscopy to visualize the distribution of bromine left faded
eosin in van Gogh's work.

Van Gogh knew red pigments of red lake were prone to fading, but he couldn't resist their vibration, Hendricks says. To make up for this, van Gogh wrote in thick strokes, desperately hoping that the extra paint would keep the colors bright longer. "The paintings wither like flowers," van Gogh once wrote to his brother Theo. "All the more reason to boldly handle them rudely, time will only soften them too much. "

 

Red pigment Red Lead (Red Lead ): the mystery of how it turned into white is solved.

Микрохимическое исследование состава грунта и пигментов

 

Red lead has been used for millennia as a pigment, from ancient Roman times to the 20th century, when society became aware of the health hazards of lead compounds. Van Gogh also used orange-red pigment, including in his landscape of 1889 "Wheat stacks under the cloudy sky" (shown below).

Researchers have long known that red lead can turn white over time - it turns into lead sulfate plus sulfur-containing carbonate mineral (hydro) cerussite after exposure to too much light. But scientists did not know the exact path of chemical degradation. Partly because the "old workhorse", an art-learning tool, is x-ray fluorescence spectroscopy, having difficulty isolating red lead from lead-white, the common white pigment of the base layer used on the canvas. X-ray fluorescence can identify the presence of an element - in this case, lead - but cannot distinguish between different chemicals containing the same element.

Last year, researchers led by Cohen Janssens Of the University of Antwerp used x-ray diffraction to determine the pathway of red lead degradation (Angew. Chem. Int., Ed., 2015, DOI: 10.1002 / anie.201411691). X-ray diffraction is sensitive to differences in the crystal structure of minerals, so the method can distinguish between red lead, white lead and other types of lead. By taking a tiny sample of paint from an art work (see Arrow) where red lead became white, the team determined the presence of a rare lead species called plumbonacrite.

It was the missing chemical link needed by scientists to determine the pathway of degradation from red lead to (hydro) cerussite.

 

 

Pigment Chrome yellow: over time, brown under the sun.

Микрохимическое исследование состава грунта и пигментов

 

To create the Sunflowers, his famous series of still lifes, van Gogh relied on chrome yellow, a family of lead chromate pigments that were introduced to the market only in the early 19th century in the 1810s. Unfortunately, the lightest shades in the yellow chromium family contain sulphate groups, which reduce the stability of pigments in light: these bright spots of yellow on the canvas become brownish-green.

Letizia Monico has held a doctoral thesis. Working with Costanza Miliani at the Institute of molecular science and technology in Perugia, Italy; Cohen Janssen From the University of Antwerp; and others found out why the color change happened.

Examining the old tubes from the chromates of lead paint and tiny samples of the paintings of van Gogh, the researchers found that the darkening happens when the hexavalent chromium becomes trivalent, the reduction, which depletes the pigment in their yellow color (Anal. Chem. 2011, DOI: 10.1021 / ac102424h ).

But other properties of oil paint can also help solve the puzzle. Oil paint dries when cross-linking unsaturated lipid chains in the presence of oxygen and dry matter - usually metal ions - is added to the paint. Metal ions combine with oxygen-generated free radicals to further enhance chromate recovery.

A team of scientists has discovered a simple strategy to slow down the inevitable blackout. When lead chromate pigments absorb blue-green light at 490-540 nm, they act as a semiconductor, releasing electrons that excite color change in chromium.

Therefore, museums could choose lighting that would avoid blue-green wavelengths of light to illuminate paintings similar to those in the "Sunflowers" series, which are determined by their yellow chromatic pigments.

 

 

Cadmium yellow: not as stable as the artists had hoped.

Микрохимическое исследование состава грунта и пигментов

 

As 19th-century artists began to realize that their favorite yellow pigments, chrome yellows, were not resistant to light, a new favorite emerged: cadmium yellow, or cadmium sulfide. In 1890-e years artists such as Claude Monet, who could afford the more expensive cadmium yellow, began to abandon the chrome yellow color, hoping that color on their paintings will be more stable, he says-a conservative from the University of Antwerp, Geert van der Snickt. Van Gogh only used yellow cadmium when he could afford it.

But one variety of cadmium yellow, called gincanico, which forms a rare hexagonal crystal system, fragile and in the long term, he adds.

Van der Snickt discovered that such yellow cadmium is vulnerable to light and oxygen.

Over time, environmental conditions turn it into cadmium sulfate, a white crystalline substance (Anal. Chem., 2009, DOI: 10.1021 / ac802518z). So when van der Snick later saw the orange-grey crust (arrow) nagelem flower of cadmium in "Flowers in blue vase" by van Gogh, he was puzzled.

Van der Snickt and his colleagues took a microscopic sample and analyzed it using synchrotron x-ray diffraction to find cadmium oxalate and lead sulfate instead of the expected cadmium sulfate (Anal). Chem., 2012, DOI: 10.1021 / ac3015627). It turns out that a few decades ago, the conservative noticed that the paint of the masterpiece peeled off and varnished the canvas to protect it - this is something that van Gogh rarely did. Unfortunately, oxalates and lead ions in the lacquer react with cadmium sulfate pigment, causing it to darken, says van der Snickt.

It's just another reminder that protective measures can sometimes do more harm than good, and that each picture is a complex bundle of materials with a unique life story. Rarely is there a one-size-fits-all solution to save a picture.

 

 

Digital restoration: the projection of the original colors to faded masterpieces

Микрохимическое исследование состава грунта и пигментов

 

Time machine

The red pigments used by van Gogh in the Bedroom faded with time, turning the purple-blue wall into blue and the pink floor into brown (shown in the image on the left). Analyzing the deterioration of the pigment of the picture, the conservatives at the van Gogh Museum released a digital version of the" Bedroom", as it would probably look when the work was only written (right).

Museum staff may be aware that the colors of the artwork have disappeared or changed, but they are not always sure what to do with it. Repainting a masterpiece to make it look closer to its original version is strictly prohibited in the Museum world, so many conservatives are considering a strategy called digital preservation, " says Ella Hendrix, a senior conservative from the van Gogh Museum in Amsterdam.

The idea is to find out the chemical composition of the painting and its history: what pigments were used and in what binders were involved colorful chemicals? Was the painting exposed to light, temperature fluctuations or humidity - the usual culprits of the degradation of the picture?

The researchers then recreate the paint recipes in a historically accurate manner and conduct artificial aging experiments on samples that mimic the effects of the environment that the picture might experience. After all, scientists use these experiments to make a reasonable assumption about the exact colors that are present at the original
dry the original, and then produce a digital visualization of the original.

Working together with colorist scientist Roy S. burns at the Rochester Institute of technology and the Dutch dyeing and coating company AkzoNobel, Hendricks focused on bringing back time to the faded red pigments in van Gogh's "Bedroom." The purple walls of the painting in 1888 turned into a blue color, because the red starch of cochineal-red-yellow
the red lake pigment, made of organic compounds, disappeared with time.

Another red pigment red lake, eosin, was used in the lines of the bed frame boards and in the red tile floor. Hendricks says the floor loses its pinkish hue, becoming more brown when the red pigment degrades.

Another advantage of digital recovery is that it's a time machine that works both ways, she notes. Moving forward, the Museum staff can use the degradation kinetics obtained for the colors of the artwork to look into the future. Using predictions about the fading of the pigment, Hendricks says that the van Gogh Museum management decided to reduce the light intensity projected on the "bedroom" when it is displayed, to 50% of its previous value, from 150 to 50-60 Lux, to mitigate color Deterioration. The team is now translating their "color time machines "technology to" an iris Field near Arles, " whose purple irises fade to blue.

 

 

Vincent van Gogh: the true colors of the artist's paintings discovered by scientists

The chemical analysis of the microscopic fragment taken from one of the three studied paintings revealed the true colors.

Микрохимическое исследование состава грунта и пигментов

 

Scientists recreated the original colors of Vincent van Gogh's famous "Bedroom" in the Yellow house in Arles, where he lived with his friend and mentor Paul Gauguin, until they broke up with the disastrous consequences for Vincent's mental health.

The chemical analysis of the microscopic fragment taken from one of the three bedroom paintings shows that the true color of the walls in the painting was purple, not the faded blue cornflower blue we see today, the researchers found.

This discovery is considered very significant because the actual walls of the real bedroom were white, so the original color of the walls in the paintings is interpreted as a bright sign of the emotional mood of van Gogh, says Francesca Casadio, a scientific restorer at the art Institute of Chicago.

"The walls of the bedroom in Arles were whitewashed. So purple is his own interpretation - his own intention to Express the peace of mind or imagination, " said Casadio.

It is very unusual for an artist to paint an empty room, so the fact that van Gogh made three paintings from his bedroom in Arles, where he hoped to create a community of artists with his friend Gauguin, is seen as an expression of his need for a place he could call home - especially since he lived in 37 places in 37 years.

Van Gogh finished his first painting in the bedroom in October 1888, which is now stored in Amsterdam. He wrote two more works in September 1889, after he cut off his ear and suffered a nervous breakdown, one work now in Chicago and the other in Paris.

Despite the fact that the walls in the painting in 1888 look today cornflower blue, the letters written by van Gogh to his brother Theo, described the colors quite differently, saying that he painted the walls of "pale purple".

 

Микрохимическое исследование состава грунта и пигментов

 

"In these letters he describes the colors of the bedroom. He wanted to make the picture beautiful, but also to Express his emotional landscape. He says he wants to paint simplicity with a bright color, " Dr. Casadio said.

A spectrogram of x-ray fluorescence of a microscopic fragment of paint from the walls of the first picture of the bedroom showed that the fading of the pigment turned a light blue color.

The original color was purple, which did not disappear from the side of the canvas, Dr. Casadio said.

 

 

"Three-quarters of the pigments you see in the Bedroom didn't exist 80 years ago. All of them were new inventions of the chemical industry of that time.

Artists used them, yellow, red, pink. Unfortunately, many of them, as we find out, change colors, " she said. "This is really important because we know that the walls in this room were whitewashed, they are not purple at all.

Thus, in the original Amsterdam painting, they convey a sense of peace and complement the other colors in the room, such as the yellow color of the chairs. It was supposed to feel at home and more peaceful, " she Told the American Association for the advancement of science in Washington.

 

 

There are facts confirming van Gogh's experiments with pigments:

- his many letters to brother Theo and close friends.

- the conclusions of scientists that a large number of pigments artists invented themselves ("Three-quarters of the pigments that you see in the" Bedroom", did not exist 80 years ago. All of them were new inventions of the chemical industry of that time.

Artists used them, yellow, red, pink. Unfortunately, many of them, as we find out, change colors », - Dr. Casadio, scientific restorer at the art Institute of Chicago)

Most of van Gogh's contemporaries also experimented with various pigments due to the limited palette of colors of the time, as they also wanted to Express their unique vision and bring something new to the world of art.

This means that the chemical analysis of the works of Renoir, Claude Monet, Klimt, Picasso, etc.must be very carefully and carefully approach to the analysis of the chemical composition of pigments.

 

 

Conclusion:

Based on the above information, it is safe to say that the results of chemical analysis and conclusions from the obtained results can often be erroneous, for the following reasons:

1. - the use of outdated technical means in the analysis of chemical composition

2. - lack of information about the original chemical composition of the pigments used by the author

3. - lack of information about external factors (temperature, light, humidity, etc.) that have affected the picture for a long period of time