An 18th-century bronze cannon used in the Battle of the Alamo has been the subject of a preservation effort to remove an unusual substance that was growing mysteriously on its surface.
The effort, led by a team of specialists from the anthropology department at Texas A&M University, involved the development and application of a special acid solution to get rid of the chalky, white substance, which recently appeared on the weapon in a rare occurrence.
It is thought it could be a byproduct of chemicals used in previous conservation efforts on the historically significant artifact.
"This is a really interesting cannon. It has a long and exciting story, especially for Texas history," Kimberly Breyfogle, a Ph.D. student in the Texas A&M Nautical Archaeology Program who collaborated on the project, told Newsweek.
The cannon is being kept at the museum of the Alamo, a historic Spanish mission and fortress compound founded in the 18th century by Roman Catholic missionaries in what is now San Antonio.
"The Alamo was built as a mission under Spanish colonial rule in the 1700s with the intention of evangelizing local Native Americans. It was used for military and medical purposes after it stopped being a functioning mission," Breyfogle said.
The Texas site is perhaps best known for the Battle of the Alamo, which took place from February 23 to March 6, 1836. This battle is considered to be an iconic event in the Texas Revolution (1835-1836)—a rebellion by U.S. colonists and Hispanic Texans (known as Tejanos) against the Mexican government.
The Battle of the Alamo was won decisively by Mexican forces, which reclaimed the mission from the Texan Army. But the revolution ultimately resulted in a split from Mexico and the founding of the Republic of Texas in 1836. The republic was later annexed by the United States, in 1845.
"During the Texas Revolution, the Alamo was besieged by the Mexican Army while a small Texan force attempted to defend it. The battle was an overwhelming defeat for the Texans, but became a rallying cry for later battles in the revolution and inspired the Texan forces to fight harder in memory of those killed at the Alamo," Breyfogle said.
Although the origin of the cannon affected by the white substance is uncertain, research suggests it was most likely cast in the 1760s in what is now Mexico and sent to the then-capital of Spanish Texas (or Tejas), Los Adaes, which is located today in Louisiana.
"It was moved around the area as needed until the Texas Revolution, and was used in a variety of important battles including the Battle of the Alamo," Breyfogle said.
Beside the Alamo, the cannon is thought to have seen action during the Battle of Medina in 1813 amid the Mexican War of Independence (1810–1821)—a conflict fought between the people of Mexico and the Spanish colonial government—and the Battle of Concepción in 1835, considered to the be the first major engagement of the Texas Revolution.
The cannon shows signs of damage—for example, it is missing several parts, such as the trunnions and cascabels.
As the Mexican Army was retreating after its defeat at the Battle of San Jacinto, fought on April 21, 1836—the final and decisive clash of the Texas Revolution—soldiers mutilated and buried their cannons so the Texan Army could not use them.
"This is probably one of those cannons: used for decades in Spanish colonial Texas before seeing action during the Texas Revolution and being destroyed and buried by the Mexican Army to prevent it from falling into enemy hands," Breyfogle said.
The white, chalky substance growing on the cannon might have posed a threat to the preservation of the artifact had it been left unchecked.
"We don't know the long-term side effects of letting the substance grow on the cannon. In this scenario, we did not want to find out through inaction," said Christopher Dostal, an assistant professor of anthropology at Texas A&M who was involved in the preservation efforts, in a press release.
"We've spent the better part of a year and a half trying to work out why this substance is growing," he continued. "It turns out, this might be a byproduct of the chemicals used in the cannon's conservation process back in 2008 and again in 2019. The substance is a precipitate of these chemicals starting to crop up on the outside of the cannon."
To develop a method to remove the white substance, Dostal and his colleagues created small bronze ingots with a similar composition to that of the cannon. The team then applied chemicals to the ingots like those used in the previous conservation efforts and conducted a number of tests to determine the best treatment.
Thanks to their investigations, the team found that a solution of formic acid was capable of removing the white substance on the cannon's surface without damaging the metal below, which they applied to the weapon using a tennis ball on a stick. This solution caused the substance to practically disappear.
During their experiments, it took several applications of the acid to completely resolve the issue. As a result, the team expects that more applications will be necessary to fully remove the powder and supplies have been left with the Alamo staff so that they can continue the process as needed.
"Although the fix is probably not permanent (yet), it was still really exciting to see the cannon once the powder had been removed," Breyfogle said.
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