The archive of a newspaper that’s more than 150 years old can conceal treasures. This is the story of a treasure rediscovered.

In the basement of the Gothic Revival building at 901 Mission St. sat, until recently, a box of negatives damaged by heat or age — probably both. The boxes themselves were decades old, the negatives inside them decades older. The label on the envelopes: “Golden Gate Bridge — Construction.” Four words that signaled something special.

At first, thoughts turned negative: These must be ruined; these can’t be salvageable. Then the inspection began, white-gloved hands pulling memory after memory from a pile that could be mistaken for garbage and carefully scanning the negatives to reveal photos that hadn’t been seen in decades.

About half the negatives showing the under-construction Golden Gate Bridge were as damaged as the boxes that held them. Bubbling and cracks scarred the surface emulsion. Many, however, were only slightly damaged. Some had no creases or blemishes at all. Cropping and light damage-repair editing made some look almost new, or as new as 82-year-old photos can look.

After the scanning came the research. Negatives like these usually don’t come with detailed caption information, or even the name of the photographer who shot them. Some have a year — 1936, 1937 — scratched across the negative’s face.

With a little digging, a story began to come into focus. Several of the shots are of the “last steel,” the stage that signified the spanning of the Golden Gate. A few images are of the “last rivet,” driven on April 27, 1937.

More than one speaker at the ceremonial event compared the final rivet, made of California gold, to the last spike of the Transcontinental Railroad at Promontory Summit in what was then Utah Territory. Alas, the rivet gun, typically used for steel, was too powerful, and it sprayed gold flakes all over the dignitaries in attendance in San Francisco. As the gun was pulled away, the rivet broke apart and disappeared. A steel rivet was used to finish the job.

No caption information is needed to grasp the tremendous scope of the Golden Gate Bridge project. At the time, the bridge’s 4,200-foot main suspension span was the longest in the world. It remains the second-longest in the United States behind the Verrazano-Narrows Bridge in New York.

Construction for the Greatest Bridge Ever Built started Jan. 5, 1933, as operators swung two large steam shovels into action at Lime Point in Marin County, digging a pit for the anchorage. Four years later, they were grading the roadway and finishing the approaches.

Despite being limited by 1930s technology, the engineers finished the project ahead of schedule and under budget. The builders returned $110,000 to the Golden Gate Bridge and Highway District upon completion.

More from Chronicle Vault

•History on the page: Read the story behind what’s arguably The Chronicle’s greatest front page: the edition of May 28, 1937, marking the debut of the Golden Gate Bridge. [Chronicle]

•And you thought your job was tough: Meet the 1950s painters who risked their lives to keep the Golden Gate Bridge that perfect shade of International Orange. [Chronicle]

•Another Bay Bridge? See renderings of some of the ridiculous cross-bay proposals over the decades. [Chronicle]

•A salute: Let’s give the king of Golden Gate Bridge stunts his due. Robert Niles is a classic San Francisco character. [Chronicle]

•Ka-boom: Remember when a major Bay Area bridge was blown sky-high over the bay? [Chronicle]

From the Archive is a weekly column highlighting more than 150 years of San Francisco stories pulled from The Chronicle’s archive. It is written and edited by Bill Van Niekerken, the library director of The Chronicle, and Tim O’Rourke, the newsroom’s assistant managing editor and executive producer of SFChronicle.com. It is part of Chronicle Vault, a newsletter that publishes at noon Wednesdays and 8:30 a.m. Sundays. Sign up for the newsletter here, and follow Chronicle Vault on Instagram. Contact Bill at bvanniekerken@sfchronicle.com and Tim at torourke@sfchronicle.com.