People squat on the ground, dipping hand-woven cloth into pits filled with dye. The fabric comes out blue. These dyers practice an ancient art. But is the art of indigo dyeing . . . dying?

Many dye pits in Kano, Nigeria, appear to be abandoned. Sons inherit the old dyeing tradition from their fathers. But they decide to work in other businesses or for the government instead. The men who remain wear sturdy gloves. They seem to have endless patience, sometimes taking six hours to dye one garment dark blue.

The homespun cloth hangs to dry on razor wire fences topping the walls around the pits. The colors range from sky blue to darkest night. The designs have names like moon and shadow, moon and star, and three baskets. (The “baskets” stand for wealth, education, and power.)

The dye pits were founded in 1498. Back then, they attracted travelers and traders from across Africa. The dye pits helped make the city of Kano one of the most prosperous in West Africa at the time. The fabrics are still used today by the African Tuareg people. Tuareg people’s skin sometimes even turns bluish from the clothes!

The indigo dye pits use no chemicals, 50-year-old Lawan Ismailu explains.

He dips his fingers into the blue-tinged foam and licks them. He smiles. “Smells like chicken,” he says. He also says indigo makes good medicine.

Some workers grumble. They say Chinese fabrics sell for half the price of Nigerian ones, taking money away from local dyers. But the Chinese fabrics are lower quality. They quickly fade.

Millions of Nigerians live in poverty. Dying dyeing just makes things worse.

Many of the abandoned traditional pits are choked with debris. But Mr. Ismailu says they keep the pits in good shape—in case indigo dyeing comes back.