Classic Mexican art stood the test of time with the help of this secret ingredient

In Gallery 209 of the Metropolitan Museum of Art sits an 18th-century wooden batea, or circular tray, from Mexico way back when it was a viceroyalty of Spain. Created by the Indigenous artist José Manuel de la Cerda, the batea is covered in jet black, shiny lacquer, which is well known as a protective and decorative coating. 

The surface of the batea is adorned with gold, orange, and red motifs of flowering trees, picturesque houses, and men on horseback to depict a scene from the Latin poem “Aeneid” when the protagonist provokes his enemy and starts a war. During his life, de la Cerda’s craftsmanship was sought after by the elite, says José L. Lazarte, the assistant paintings conservator at the Met. 

“It’s just such a beautiful thing to look at, and totally worth it for a court of any sort,” he says. Bateas like de la Cerda’s were not only popular in Mexico, but were also prized among European royalty. The art pieces were even captured in Spanish still lifes, Lazarte says. 

While it takes incredible mastery to create art like de la Cerda’s lacquer war scene, it also takes considerable expertise to preserve such art for centuries, or even millennia, so people can marvel at it today. That’s where conservators like Lazarte come in. But to be able to safeguard a piece for generations to come, he needs to know how it was made and what it was made of to tailor the treatment. 

Therein lies the challenge. Most of the scientific techniques and resources used by conservators are specific to Western European art, leaving a big gap in knowledge when it comes to the rest of the world, including colonial Latin America. 

“There are a lot of assumptions that are made about Latin American [art] based on European works,” Lazarte says. In an effort to fill that gap, the Met, the Hispanic Society Museum & Library (HSML), and Weill Cornell Medicine in New York City are collaborating on a project that focuses on one special material, chia oil, and how it might have been used as a binder and drying agent in Mexican masterpieces like de la Cerada’s. 

Funded by a two-year Research and Development Grant from the National Endowment for the Humanities, the researchers will start by analyzing five pieces of lacquerware that were created between the 16th and 19th centuries. They will then apply their findings to the analysis of several paintings from the same geography and era.  

Mexican lacquerware has a long history that extends to as early 500 B.C.E, far before the Spanish ever set foot in the Americas. “Lacquer is one of the most complex of all the Mexican folk art,” says Marta Turok, the coordinator of the Ruth D. Lechuga Center for Folk Art Studies at the Franz Mayer Museum in Mexico City. (She is not directly involved in the project.)

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To create lacquerware, a paste is made from many ingredients, including the fat of a scale insect called aje, a pigment with the desired color, and some type of drying oil. The last component helps bind all the ingredients together, keeps the mixture liquid long enough to work with it, and ensures the lacquer dries as a shiny, durable surface when applied to wood, says Monica Katz, the former objects conservator at the HSML.

While European art used linseed oil, made from flax seeds, as the standard drying agent, there is evidence to suggest that artists in colonial Mexico were using chia oil. The chia plant is native to the Latin American country and has had many culinary, medicinal, and religious uses throughout the centuries. To harvest the oil, some Indigenous communities toast and grind the plant’s seeds; afterward, they add a bit of water to form a sort of dough, and then wring it out with a cloth. Every day they twist it a bit more to slowly extract the oil drop by drop, according to Turok.  

Chia oil was used as a drying agent in pre-Hispanic, Indigenous lacquered gourds. But experts aren’t sure how extensively it was used after the Spanish colonized Mexico. Studying localized art techniques through historical records can help conservators understand different patterns—but because the vast majority of the surviving documents were written by colonists, the descriptions are far from objective. 

“They saw what they wanted to see,” Katz says.

So, the collaborators from the three institutions are turning to new scientific analyses to identify the materials themselves. “The objects can’t lie to us,” Katz says. 

But the methods they’re testing have their own pitfalls, many of which mirror the issues with the historical documentation.

The fields of heritage and conservation sciences are growing rapidly, but many of the tools available today are geared toward Western European art and specifically, inorganic materials, says Julie Arslanoglu, a research scientist at the Met and one of the principal investigators.

There is currently no method for identifying chia oil in art or distinguishing it from other drying oils like linseed, according to the Met. Around 2014, a de la Cerda lacquered writing cabinet owed by the HSML was sent to the Museum of Fine Arts in Boston for an exhibit; in return, the museum’s furniture conservators ran exhaustive tests on it. They were able to learn what pigments were used in the painted decorations and lacquer, what materials were used in the preparation layer, and even what type of wood the cabinet was made from. But they hit the limits of their methods and weren’t able to figure out exactly what the drying oil was. 

“When we get to other types of oils or materials that are used in the rest of the world, there are efforts to characterize it or classify it,” Arslanoglu, a research scientist says. “But it doesn’t have that same definitive identification.”

Deep-dive projects like this are important to start building a material timeline, says Lazarte, also one of the principal investigators. 

Because the researchers can’t rely on much of the historical documentation to identify the materials in the Indigenous Mexican art, there are very few scientific reference materials. While it can be frustrating to start from scratch, they say, they’re also exciting to draw a road map for future studies.

“What we want to show is this is how you could do this for any material that’s unknown,” Arslanoglu says. In this way, they could help create a methodology “to let the objects speak about where they came from, how they were made,” she adds.  

To identify chia oil in the objects, the researchers are looking primarily at three markers: lipids, proteins, and DNA. But they’re casting a wider net with their analysis because one technique might not work on its own—something Arslanoglu and her colleagues have found to be true more often when analyzing materials outside the purview of classic Western European artists.

To identify chia oil in the objects through its lipids and proteins, the researchers are using two forms of mass spectrometry, which involves breaking up a big molecule into smaller pieces that are easier to “read.” Proteins, for example, get split up into smaller chains of amino acids called peptides; the pieces are then ionized so the researchers can look at the mass-to-charge ratio for clues that help identify the source of the molecule as a whole. But characterizing the proteins for chia oil can be difficult, even with mass spectrometers, because there are far fewer public databases to reference for plant peptides versus animal peptides, Arslanoglu explains.

“Collagen has been sequenced for pretty much every animal on the planet very, very well. So if you want to go find out the collagen sequence of a hippo, you’ve got at least some sequences in the database that will help you,” she says. 

Chia peptides, on the other hand, have not been DNA sequenced at all, which means the researchers have to turn to the more time-consuming approach of de novo sequencing. They break down each sample and ionize it twice to reconstruct the original molecule, rather than using databases to find a match with an already-known substance

And while Arslanoglu says the lipid profile between chia and linseed oil might be similar, the molecules themselves are not. “If [chia oil] was used, it should be chock full of chia DNA,” says Christopher Mason, a professor of genetics, physiology, and biophysics at Weill Cornell Medicine who is tasked with DNA analysis. His method of sequencing can also provide a wealth of information beyond chia oil.

To demystify the ingredients of the lacquer, Mason is trying shotgun sequencing, which involves identifying all the genetic codes in a sample, even if they’re tiny fragments. Even though they are primarily looking for chia DNA, there is still a lot of information to be gleaned from the rest of the DNA present. 

“You can still discern if it’s plant, animal, human, microbial, or viral DNA,” Mason explains. “You can tease it all out.” 

As a result, the oil becomes a “time capsule,” he says, storing all the DNA that was present when it was painted onto the lacquerware. That could include traces of any plant pollen in the air while the object was made, or the ancestry of the original artist.

“It’s like doing 23andMe on a painting,” Mason notes. 

But to do this analysis, Mason says he will need extensive control samples to ensure he is not just detecting the DNA of all the people who have handled the object over the centuries. 

While the project’s primary inspiration was to identify the type of oil used to better conserve Indigenous Mexican works, the implications of this research could reach further.

The materials in a piece of art can open up a window into the global trade of the era and show where the artists were using materials from local sources, Europe, or across the world. When Mexico was colonized by Spain, it forced a birth of new cultures and identities over the next 300 years. Studying materials like chia oil can hint at how these interactions played out in everyday wares and objects.

“The more you know about the materials of the object, the better you could be at interpreting that object and also telling its story,” Arslanoglu says. 

[Related: The ancient Mexican city of Monte Albán thrived with public works, not kings]

What’s more, determining what techniques and materials artists used in the past can help preserve Indigenous traditions today. Since the 1990s, Turok has been working with Mexican lacquerware artisans to create more durable pieces that can withstand the test of time. As they looked back on older examples, they noticed that the lacquer used in the late 20th century to today was coming off in chunks, whereas the 18th and 19th century decorations were still in good shape. Through historical research, Turok and her colleagues found lists of materials but no instructions. Some of the artisans, however, suggested that the reason the older pieces were faring better was due to the possible use of chia oil. 

 “We really relied on some of the older, traditional artists,” Turok says. “It was oral tradition being handed down.”

The majority of the modern crafters Turok was working with used linseed oil in part because it was 10 times cheaper than chia oil. But when one expert demonstrated his method of applying heated chia oil to a damaged piece of lacquerware, the coating stopped caking off. Turok says this could be because chia oil helps rehydrate the lacquer and protect it against changes in humidity.

According to Turok, the results of this project with the Met would not only aid conservators like her, but also potentially help keep the practice alive for years to come. Doing so requires a deep look at the materials to understand the people behind the lacquerware.

“When you start to think about how [art] was created, someone had made all of those choices,” Arslanoglu says. “This gives you another way to appreciate all the things that affect an artist. It’s not just making beautiful things—it’s the history.”