The Pharaoh Apries was not exactly popular. He lost his kingdom to someone who, according to Herodotus, once farted in his face, and in 570 BC was strangled by the Egyptians he once ruled. But he had an excellent palace. Built in the northern part of the ancient Egyptian city of Memphis, Apries’s palace was a sprawling 524 feet by 354 feet. The Pharaoh would enter the grounds through an enormous gate decorated with seven limestone reliefs, one of which depicted the pharaoh under a star-filled blue sky. Other scenes have been lost to time.

Though the colors of these reliefs have dulled to what seems now like variations on tan, they were once spectacular, with vivid greens, creamy whites, and brilliant Egyptian blue. Now, an international team of archaeologists has analyzed paint samples from Apries’s gate and found two, unexpectedly “new” yellow pigments that have never before been identified in Egyptian antiquity art. “We did not initially have a clue of what they were,” says Kaare Lund Rasmussen, a chemist at the University of Southern Denmark and a co-author of the group’s study, published this summer in Heritage Science. Other team members are based at the Glyptoteket in Copenhagen, the British Museum, and the University of Pisa.

The ruins of Apries’s palace in Memphis. Neithsabes

With an abundance of Egyptian palatial ruins to choose from, the team decided to study Apries’s because it was constructed after a long period of isolation, at a time when Egypt had opened up contact with the Mediterranean and constructed a trading colony on the Nile Delta, Rasmussen says. “We thought that maybe we could contribute to the enlightenment of the Greek-Egyptian relations and the exchange of culture between them,” he says.

When researchers analyze pigments found in old paintings, they often take samples smaller than a millimeter in in length, order to preserve the image. But with massive Egyptian sculptures, scale is less of an issue. The samples from Apries’s gate ranged from 10 to 20 square centimeters. “They are small on an Egyptian scale, but certainly not microscopic,” Rasmussen says. The researchers studied a column adorned with palm fronds and four relief fragments. The full scenes have long since crumbled away, but they depict a number of recognizable subjects, including a lotus leaf, half a loaf of bread, and the name of the jackal god Wepwawet.

Some of the gate fragments analyzed. The bottom two have been painted with lead-tin and lead-antimonate yellows. Ole Haupt

The researchers ran each fragment through a battery of non-invasive tests, including microscopy and examination under ultraviolet fluorescence. At first, the paint told a familiar story: Several pigments were commonly used in Egypt at the time, such as white made from gypsum, green from atacamite, red from hematite, and Egyptian blue from copper. But the yellows proved much more vexing.

Most yellow pigments that the ancient Egyptians were known to use consisted of yellow ochre, a mixture of clay and iron oxide. People have painted with ochres for hundreds of thousands of years: The earliest example dates back 285,000 years, at the Homo erectus site GnJh-03 in Kenya, according to LiveScience. Other ancient Egyptian yellows included orpiment—an arsenic sulfide mineral that glittered as brilliantly as gold but, as its name suggests, was dreadfully poisonous—and iron sulfates that produced pigments the color of a lemon.

The researchers detected arsenic, lead, and antimony in the yellow paint—meaning it was more than just orpiment. Kaare Lund Rasmussen

The researchers expected the yellow lotus leaf fragment to be a pigment that archaeologists were already familiar with. “We all thought that the yellow color must come from orpiment,” Rasmussen says. Research on Egyptian painting after the Bronze Age shows that Egyptians often painted large-scale reliefs using a mixture of orpiment and yellow ochre, the authors write. (Pure orpiment was reserved for the gilded look of sarcophagi.)

But after analyzing the pigment with micro-X-ray fluorescence spectroscopy, they found clear traces of arsenic, lead, and antimony. “We realized of course that this could not be only [orpiment],” Rasmussen says. The elements they detected suggested the presence of other lead-based components, specifically lead-antimonate yellow and lead-tin yellow. The fragments they examined also included a superficial layer of wax, which Rasmussen speculates might have made the yellow even shinier. “Maybe they tried to emulate the luster of gold,” he says.

Lead-tin yellow, which was discovered at the Palace of Apries, also appears in “The Milkmaid” by Johannes Vermeer. Public Domain

These lead-based yellows were way ahead of their time: They had previously been found in paintings dating back to the Middle Ages, with lead-tin yellow appearing in the 14th century and lead-antimonate yellow appearing at the beginning of the 16th century. Lead-tin yellow can be spotted prominently in Johannes Vermeer’s “The Milkmaid,” painted in either 1657 or 1658. Both pigments disappeared from popular use in the mid-19th century. “The Egyptians at this time had the technology to either manufacture these pigments, which would be amazing, or had the knowledge to identify them and the knowledge where to find them in nature,” Rasmussen says.

The authors now believe that these pigments originated in Egypt, but they hypothesize that Europeans “(re)invented” them during the Middle Ages. Now that the researchers have pushed back the historical timeline of sophisticated yellow paints, they hope to hunt down any other uses of the pigment in the ancient world. With ancient trade routes in mind, Rasmussen knows where he wants to start looking. “Could it be in Greece?” he asks.