Today it stands on a picturesque square in the capital, discolored and allegedly damaged by a careless restoration team — a casualty, officials say, of an act of monumental boneheadedness.

Last week, Mexico’s National Institute of Anthropology and History issued a report alleging that a restoration job ordered by the city government was botched and has resulted in “irreversible damage” to the historic bronze, which was cast before Napoleon declared himself emperor of France.

Experts claimed they found the culprit on scaffolding at the work site: a bucket containing a 60% nitric acid solution. The use of such stuff, they said, has been known for decades to be a bad choice for metal restoration work, and its application has caused new corrosion and discoloration, affecting more than half the surface of “El Caballito,” which means “The Little Horse,” even though it’s nearly three stories high.

The institute has pledged to bring legal action against the contractor, Marina Monument Restoration. King Carlos’ newly splotched face has appeared on the front pages of the major newspapers. And Mexicans — who tend to be as proud of their history and culture as they are wary of their government — have reacted with collective exasperation. A cartoon ricocheting around Twitter depicts the statue scrawled with a new imagined name: “La Burradota,” literally “the big burro,” but colloquially “the big screw-up.”

The scandal is proof, if any was needed, that art restorers are the field-goal kickers of the culture world — specialists whose work tends to go largely unnoticed until they shank a big one. In this case, however, the owner of the restoration company, Arturo Javier Marina Othon, is pushing back. In a public statement, he said the stains were ancient, his methods were justified and the story had more to do with a government too dysfunctional to care for its cultural heritage.

“I’m not lying when I say that 90% of the sculptures and monuments at the national level are in deplorable shape,” he declared.

Marina argued that his solution was only 30% acid and was perfectly safe for cleaning the layer of grime that accumulates on outdoor statuary. In a fiery five-page letter, he painted himself as a scapegoat, declared himself a passionate advocate of the “history of the fatherland” and denounced the government for failing, he said, to protect Mexico’s cultural treasures.

The controversy threatens to be a problem for Mexico City Mayor Miguel Angel Mancera, who does not need another stain on his short record in office. He and his team, who took the reins of the city in December, have been widely criticized for their handling of a case this year in which a dozen clubgoers were abducted from a bar and slain. Adding to the pressure, both of Mancera’s most recent predecessors had counted the restoration of Mexico City’s historic core as a signature achievement.

On Wednesday, Mancera declared that his government would “act firmly to establish responsibility.” A day later, city officials in charge of the capital’s historic zone announced that they had met with the experts from the institute, who, apparently contradicting their initial report, assured the officials that the damage could be reversed.

“El Caballito,” the work of the great Spanish neoclassical sculptor and architect Manuel Tolsa, has seen its share of controversy. After Mexico won its independence from Spain in 1821, the statue was, understandably, deemed out of sync with the national mood and was moved from Mexico City’s main square into storage. It eventually landed in its current spot in front of the National Art Museum in a plaza named after Tolsa.

On Friday morning, the statue was obscured by blue sheeting that had been wrapped around a barn-like scaffolding. A number of Mexicans hurrying to work could be seen peeking through the sheets to get a glimpse.

“This is one of the monuments we’ve admired for years,” said Ruben Ramos Calderon, 59, a worker in an accounting office. “Instead of doing something good, they’ve damaged it.”

The Mexican press, meanwhile, has been using the opportunity to remind its readers of the way bronze statuary is spiffed up in the city of Juarez. Officials there claim that Valentina, the cheap and popular hot sauce, works like a charm.

Cecilia Sanchez of The Times’ Mexico City bureau contributed to this report.