Though modern house paint is usually a benign mix of synthetic pigment, acrylic, water and fillers like clay or zinc oxide, in earlier eras, creating paint was a dangerous business. While some colors came from harmless organic sources — curdled milk, charcoal, mild mineral ores — others were toxic or unstable. Modern safety regulations have made scarce or extinct some of the shades that made historic structures and great paintings so vibrant: the lead-derived white that Vermeer used to depict sunlight; turbith mineral, or “queen’s yellow,” made from a mercury-based concoction; the arsenic-derived hues of the wallpaper that papered Napoleon’s prison home on the remote island of St. Helena (which some historians believe may have contributed to his death).

Much of Felgueiras’s time is spent tracking down the dwindling supplies of arcane ingredients to recreate these historical hues. There is ivory black, made from charred antique elephant tusks; cochineal, a lush scarlet pigment derived from crushed South American beetles, and vermilion red made from mercury, which is both poisonous and relatively volatile.

Still, some colors remain tantalizingly out of reach, including Arrabida red, which was sourced from a special limestone only found in a defunct Portuguese mine. “Mixed with white pigment, it explodes into incredible pinks,” Felgueiras says. “But for some reason, the elderly woman who owns the mine doesn’t want to reopen it again just for me.” Lost forever, as well, is Indian yellow, a transparent fluorescent glaze made from the urine of cows in rural India that had been fed exclusively on mango leaves. The color, which Felgueiras describes as “heartbreaking,” disappeared because the cows were undernourished by the leaves, which contain urushiol, the noxious ingredient in poison ivy. But Felgueiras never gives up hope that someone is hoarding a vial or two.

At any time, Felgueiras is working on just a handful of colors; generally, he can only complete one a day. The mixing process is arduous: Hand-grinding pigment can take hours, and the linseed oil, which binds the pigment, must be added carefully. Once applied, Felgueiras’s oil-based mixtures can take up to a week to dry entirely. Ancient finishes such as copper verdigris glaze, a metallic green, which was born in the Roman era and later revived during the chinoiserie craze of the 1750s, can require several coats to achieve the desired effect. And unlike today’s paints, which are designed for easy application and longevity (“Basically plastic,” Felgueiras says, with revulsion), some of these hues are, by nature, unstable. Van Gogh once wrote that “paintings fade like flowers”; today, art conservators have an evocative descriptor for the chameleon nature of such paint colors: fugitive. “They don’t just fade, they actually change,” Felgueiras says. “Which is part of their beauty.”