Unidentified growth removed from Alamo cannons

televisionResearchers at Alamo A&M University have been working to resolve a conservation issue with an 18th century bronze cannon used in the Battle of the Alamo on March 6, 1836. An unknown white powdery substance has been growing on the surface of the bronze four-pounder cannon. This substance has not been found on any other bronze or iron cannon at the Alamo Museum.

The cannon was located in central Mexico and subsequently deployed to the border, where it took part in several battles, including the Battle of Medina in 1813, the largest land battle in Texas history. At some point, perhaps during the Battle of Concepción in 1835, it was captured by the State of Texas and brought to the Alamo. It was made using a sand casting technique with an unusual metal composition. The team found lead and other atypical metals in the mix, and casting defects and bubbles were clearly visible. Given the limited technology of the foundry, it is surprising that the cannon survived decades of battlefield combat without ever exploding.

“We spent a year and a half trying to figure out why this substance was growing,” Dostal revealed. “It turns out that it was probably a byproduct of the chemicals used during the restoration of the cannon in 2008 and 2019. This substance was a precipitate of these chemicals and it started to appear on the outside of the cannon.”

To replicate this result, Dostal and Breyfogle made their own bronze blocks with a similar composition to the cannon. They then applied the same method and treatment to these blocks.

“This is a rare case and it took us a lot of time to figure out the exact cause,” Breyfogle said.

They are not sure what the white substance is, but it is a precipitate from an electrolysis process that was previously used to clean the cannon. Instead of cleaning it, the corrosive chemicals in the electrolysis tank combined with the non-standard metal composition of the cannon and formed carbonate crystals that are now damaging the surface of the cannon.

To remove the white substance and prevent it from reappearing, the researchers used another chemical, a solution of 5 percent formic acid and deionized water. It removes the chalky deposits without damaging the bronze underneath. They applied the solution to the outside of the cannon with a cloth and then used a tennis ball with a stick to apply it across the entire bore of the cannon. The white substance disappears on contact, but restorers had to apply the solution several times over the course of several months. The process took place in full view of the public. Now, the cleaned cannon is complete and back on display at the Alamo Museum.

The hope was that this chemical wouldn’t suffer the same unintended consequences as the last one, but ultimately the conservation team preferred to risk using a diluted organic acid that the cannon might encounter as it rolled over an anthill, nettle, or pineapple, rather than allowing the white substance to proliferate, with its potential long-term side effects.

Because the team’s restoration of the cannon takes place during the museum’s normal hours, many school groups are able to observe the process, and Lanham said their conservation work also has a valuable educational dimension, inspiring the next generation of historians and conservationists.