Paul Gardullo lifted an iron ballast from a Portuguese slave ship that sank in 1794 out of a crate Wednesday morning and hefted its weight in his hands.

“Anytime I come into contact with the objects from the São José, it’s an incredibly moving experience,” said the curator of the Smithsonian’s National Museum of African American History and Culture. Artifacts from the São José–Paquete de Africa arrived Wednesday at the museum’s storage facility after a research-and-recovery project that’s been going on since 2010.

The long, rectangular ballasts, used to hold the ship down, offset the weight of its human cargo and kept it balanced in the water as it carried 512 enslaved Mozambicans across the sea.

“In some ways, [they] stand, in the case of this particular ship, for the people who were enslaved on board,” Gardullo said. “This ballast that’s here with us … is incredibly important … because of its symbolic and almost spiritual status of standing in for human beings. It’s our job to recalculate the weight of this iron, not as slavers did, but according to a new moral compass—one that hopes to make the mute iron speak for the souls of those lost on board.”

The São José sank in turbulent waters in December of 1794, so near to the shores of Cape Town, South Africa, that the vessel was able to signal for help. The captain, crew and about half of the captives were rescued, but 212 Mozambicans drowned. The survivors were resold into slavery in the Western Cape. Some of the ballasts from the vessel are among artifacts that are being loaned to NMAAHC for a decade. Researchers also found the remnants of shackles. This is the first historically documented shipwreck with enslaved Africans aboard.

An international research partnership, the Slave Works Project, spearheaded the discovery of the São José wreck. It includes researchers from George Washington University, NMAAHC, the U.S. National Park Service and the Iziko Museums of South Africa (Iziko). Working the site of the wreck was a challenge for divers because of strong currents and churning sands.

“When the wind is in the wrong direction, it isn’t divable at all,” said Jaco Boshoff, a maritime archeologist with Iziko who is principal investigator at the site of the wreck. He was with Gardullo when the iron ballast was unpacked Wednesday morning, and they lifted it together. “It’s a rough site. That’s why the wreck isn’t intact. It’s scattered all over the sea bed.”

While scientists are supposed to remain objective, Boshoff said that divers sometimes became emotional while working, especially on days when they had to deal with rough seas and they were being shaken up underwater.

“You come up and you think about it—it’s a tough dive, and you start realizing these guys were shipwrecked and they had to fight for their lives,” Boshoff said. “In this sea, they didn’t have what we had on, wet suits and scuba gear, and those guys had nothing. … Then it starts hitting home.”

At a reception Wednesday night celebrating the arrival of the artifacts at the Embassy of South Africa, the ambassador for the Republic of South Africa, H.E. Mninwa Mahlangu, spoke of the significance of finding this wreckage off the Cape Coast in an affluent area now known as Clifton Beach.

“Clifton is usually associated with beach parties and huge mansions, not slave-ship wrecks. It is therefore ironic that this site of pleasure also conceals a layer of calamity and pain,” the ambassador said. “The unfolding narrative of the São José is a powerful reminder that South Africa has emerged from a past scarred by the injustices of slavery, colonial conquests … and labor exploitation.”

He added that a global approach is needed to uncover the story of slavery and its legacies.

“The legacies of slavery and colonialism, such as racism and economic exploitation, persist, and in researching this significant history of slavery, we should be mindful of how the knowledge will help us comfort and overcome these legacies,” said Mahlangu.

Iziko’s Boshoff, a white South African, thinks the find is vital for his country because people don’t understand how pervasive the slave trade was. He also noted that there could be descendants of the Mozambican slaves who survived the wreck.

“Although I am a white person, I might even have some of that blood in my veins,” Boshoff said. “If your ancestors have been in South Africa for more than 200 years, this myth of pure race doesn’t exist. It’s just not possible. For me, in a sense, that makes it more valuable.”

The Smithsonian’s Bunch said that the artifacts will remind people that the effects of slavery still exist in everything, from the way race relations have played out in America to the fact that the economic engine for almost every nation in the world was the slave trade. It’s a global story, Bunch said, but he wants the exhibition to have a special message for African Americans.

“The key here is I want to help people overcome any fear, any stigma, any sense that ‘I’m a little embarrassed that my ancestors were enslaved,’” Bunch said. “When I walked down the ramp that they walked down and … saw that beautiful ocean … I was trying to imagine what it was like to basically look back and realize you’re never going to see your land again, but you’ve got to keep moving forward.”

Bunch added: “That notion of ‘I wish I was as strong as my enslaved ancestors’ is what I hope a lot of people will get out of this.”

The artifacts from the São José will be featured at NMAAHC in the exhibition “Slavery and Freedom” when it opens Sept. 24, 2016, which coincides with South Africa’s celebration of Heritage Day.