Later, Sarah Mastrangelo would remember the eye, how it suddenly appeared, staring up at her from within the belly of the empress of Mexico.

She gasped.

“What is that?” she said out loud.

A photographer standing next to her peered over to take a look.

“It’s an eye,” he said.

She looked again. What’s it doing there? Why is there an eye hidden beneath the empress’ heavy robes? “Have I been staring at this too long?” she wondered.

Mastrangelo is an art conservator, someone used to finding things that don’t look the way they necessarily should, things that appear where they shouldn’t necessarily be, particularly with very old paintings like the one she was working on.

But not this, never this.

All kinds of thoughts flitted through her mind as she looked at the eye, bathed in infrared light. In the ordinary light of day, there was no eye to see. But under infrared light, there was no mistaking it.

Mastrangelo first encountered the eye in 2017, when she was scrutinizing works for possible exhibition in the Philadelphia Museum of Art’s enormous new suite of galleries — the Robert L. McNeil Jr. Galleries dedicated to early American art — as part of the $233 million transformation of the museum’s inner core, opening to the public May 7.

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Because the 22,000 square feet of new gallery space would house a rethought narrative of early American art, conservators were poring over many works related to Indigenous culture, enslaved people, and paintings and objects produced by competing European strongholds, particularly the Spanish Empire.

Many of these works had not been on view for decades — if at all.

And that is why, when the Frank Gehry-designed galleries open Friday, paired formal portraits of Agustín de Iturbíde, emperor of Mexico, and his wife, the empress, Ana María, painted by Josephus Arias Huarte in 1822, will be on display, hung in a prominent corner.

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But that is not all that will be there.

These two portraits are actually four portraits.

What Mastrangelo, 30, eventually found beneath the Mexican portraits, hidden away like shadowy palimpsests of an earlier order, were two very fine portraits of the king and queen of Spain, Charles IV and Maria Luisa of Parma. They are still there, hanging upside down beneath the painted Iturbídes.

It was Maria Luisa’s eye that Mastrangelo first encountered over three years ago.

As she peered through the eerie infrared light, Mastrangelo first thought the eye could be a painter’s sardonic allusion to the empress’ endless labors producing her 10 children, a private mark left by the artist, Huarte, beneath his final layer of paint. Perhaps it had some other, hidden, even magical significance.

Although the Iturbídes have been in the museum’s collection since 1922, they have been exhibited sparingly, most recently about 20 years ago. And they had never been seriously scrutinized before Mastrangelo began looking closely at them.

It was about time.

The empress of Mexico — she liked to be called Madam — fled that country after her husband was executed in 1824. She brought their portraits as she made her way circuitously to Philadelphia, arriving in the early 1830s and then living for 30 years mostly at 226 S. Broad St., now a Michael Graves-designed concrete parking garage. (Known for her piety and taste for luxury, Madam now lies in the burial vault of her church, St. John the Evangelist Church on South 13th Street, near City Hall.)

Given this history, Mastrangelo could tell the portraits had been through a lot — not surprising since Madam had probably rolled them up for her travels. Mastrangelo could clearly see how previous conservators sought to cover up damage by painting over cracks and filling in gaps where there had been large losses of paint. The canvases bore a kind of toxic sheen from clouds of yellowed varnish.

By any measure, then, the paintings would represent a challenge to a conservator, although at that point it didn’t seem like an unusual one.

After giving the paintings the once-over with her naked eye, Mastrangelo put them under the microscope. That’s where she first got the inkling that something more was going on, something odd.

The empress’ image appeared to have two “grounds” — two layers of paint, not one as would be expected — laid down by the artist to create an appropriate surface for his work. And there was paint separating the two red grounds.

“And so I was like, ‘This is very curious, especially because there’s these blues. I know they should be red grounds, but why am I seeing blues and grays and whites?’” she recalled. “I was like, ‘What is happening?’”

It was at that point she decided to look at the work under infrared light with a special camera. And then the eye appeared, staring up.

“Everything was like the usual, OK, I see nothing, all right, fine, fine, fine. And then, ‘Oh my God!’” she said.

Mastrangelo had been looking very closely at the paint surface through her infrared camera lens, and when she pulled the camera back from the canvas, the eye became part of “this ghostly face of a woman.”

Because the red ground of the painting absorbed so much of the infrared light, that ghostly face was all that Mastrangelo could make out. Time to bring in the x-radiography.

“It was like boom!” Mastrangelo recalled feeling when the hidden portrait materialized like a solidifying poltergeist beneath the x-rays.

Mastrangelo could barely contain herself.

“Get out of town! I was so excited,” she said. “It was just so thrilling to [see] these really beautiful finished portraits just underneath these paintings. They’re flipped upside down, so you have to rotate them 180 degrees to see the portraits. And as you start really exploring these portraits, you realize, actually how nice they are, the ones below. …

“It was clear that it was a different artist, and that, looking at the technique, it was technically better and stylistically, it was very different, and I could tell from the dress and just the way the costumes were in the ornamentation that it was from decades earlier, an earlier period.”

Much more study is needed. Mastrangelo believes the portrait of Charles IV is an excellent copy of a portrait of the king by Goya.

Why would the king be obliterated by another painting? Probably for a practical reason — canvas was in short supply in Mexico and when Iturbíde seized power and a coronation portrait was desired, Charles and Maria Luisa became expendable. After all, they represented the old order anyway.

“It’s not a coincidence that this was the king and queen,” Mastrangelo said. “Constantly things are being reused, canvases are being reused, but the fact that it’s the king and queen of Spain, you know, being replaced with this new emperor and empress just fits. Stuff like that was definitely purposeful.”

There are other revelations to be found in the museum’s reinstallation of American art. Some of these works, like the portraits of the Iturbídes, and a historically intriguing painting of a Black youth with a parrot, have given up secrets precisely because they have been looked at with fresh eyes keen on rethinking the question What is important in understanding the origins and development of American art?

The youth with the parrot, probably in the museum collection for a century, has never been on exhibition.

Mastrangelo also worked on that piece, an image in which the subject is holding a North American bow in one hand and a parrot in the other. No one can say who painted it. But Mastrangelo believes it was originally part of a much larger painting, now lost.

Kathleen A. Foster, the museum’s senior curator of American art, noted that the figure is dressed in fine silks and is surrounded by vegetation reminiscent of South America.

“We think it’s like from the middle of the 17th century, the artist isn’t known, although it may have been painted in Holland by a Dutch artist,” Foster said. Or in Brazil, which had a Dutch colony.

“It opens up this whole story of transatlantic cultures,” Foster said. “The point is, we’ve got four different continents represented in this little painting, and it, it represents the tangle here of cultures.”

Other works, like Charles Willson Peale’s famous Staircase Group (1795), with its illusion of an actual staircase leading up from a step on the gallery floor, have been studied and buffed and rebuilt until their familiarity is now like a gallery beacon.

Lucia Bay, 41, the museum’s associate conservator of paintings, researched 18th-century door frames and steps and moldings for her Staircase work. She read everything she could find about how the painting was displayed by Peale in 1795 when he hung it in his museum at the American Philosophical Society, Fifth and Chestnut Streets. What would be the most authentic way to maintain the illusion of a stairway disappearing up into the darkness?

(And of course she spent countless hours repairing innumerable cracks in the painting, largely at shoulder height, probably made by all the people walking up and poking. Are those stairs there?)

Still other works, like an elaborate bedstead that belonged to Joseph Bonaparte, Napoleon’s older brother, underscore the city’s imperial splendor in antebellum America, when Philadelphia was home to exiled royalty like himself and the empress of Mexico.

Bonaparte lived in Philadelphia as well, at 260 S. Ninth St., before he departed in 1816 for his newly built estate, Point Breeze, in Bordentown, Burlington County.

“Every time we reinterpret and reinstall a big part of the collection, it becomes a juggernaut of conservators and curators working together to find new ways to look at the collection and to explore more deeply what we have,” said Mark Tucker, 66, the museum’s director of conservation. “The expansion of gallery spaces and the development of new interpretive approaches as you see in the American galleries, it’s a huge motivation to explore the depths of the collection, and as a result we found some remarkable objects.”

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