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Thank you for joining the St. Augustine Lighthouse & Maritime Museum for Mission Accomplished: Preserving a Revolutionary War Shipwreck. This is the second of a four-part series showcasing the Museum mission to discover, preserve, present, and keep alive the stories of the nation’s oldest port as symbolized by our working St. Augustine Lighthouse.
As mentioned in the previous Mission Accomplished segment, artifacts look like “lumps of rock” called concretions when archaeologists find them on the ocean floor. Also discussed was removing concretion material from the cannon, a messy job done outside. In this segment, you’ll find out what happens after the concretion is removed and how other, smaller concretions are conserved and made ready to display in an exhibit.
At the shipwreck site or shortly after arriving in the lab, objects “vitals” are taken, including measurement and weight, and each concretion is photographed.
All objects have to stay submerged in water after removal from the ocean so they won’t rust away in the air.
Unlike cannon, you can’t tell what the smaller objects are just by looking at them. This concretion is pictured shortly after archaeologists brought it onto the research vessel. Taking a que from doctors, artifact conservators use X-rays to see what’s inside smaller concretions.
Here is its X-ray. Look closely. What do you see?
Did you see the hammer, padlock, and nails and lead shot?
Here’s another concretion, and here’s the X-ray from it. Again, look closely. What do you recognize in this X-ray? This one is especially interesting because of all the different objects in it. Did you see a pistol, hook, lead shot, iron spike, medallion, a ring, and a hank?
Notice the ring and the hank, which was used to hang sails on yard arms, are nearly transparent. This is because there is nothing left of the actual object. It is just a cavity in the shape of the original object that rusted away inside the concretion. The brighter objects showing in the X-ray are less deteriorated. Knowing what’s inside in advance helps conservators plan the next steps of conservation before removing the concretion. With ring-shaped cavities, conservators will drill a small hole into the concretion and fill the void with epoxy to make an exact replica of the now-gone artifact.
The pistol, as another example, has several types of materials, including different metals and a wooden handle, all of which will need different types of treatment.
With the X-ray in hand, the next step is to remove the concretion from around the objects. Smaller objects require more delicate treatment than the hammer and chisel used on the cannon. Conservators slowly and carefully chip away at the concretion using an air scribe.
Once an object is dislodged from the concretion, it is immediately submerged in water to await to the next phase.
The main problem to solve on objects shipwrecks is removing the corrosive salt that gets chemically bonded to the objects. Without proper treatment, the salt will turn artifacts, especially iron ones, into rust pretty quickly once exposed to air. You can see that with these untreated cannons in this picture.
Museum Conservators use a process called electrolysis. First, the object is placed in a container and hooked up to a low-voltage electrical current.
Then soda ash is dissolved in purified water.
Once poured into the container, the soda ash interacts with the electrical current to to chemically remove the salts over time.
Ph and salt levels in the water are routinely checked, and when salt levels get high enough, the water is drained and replaced and the process continues. When the salt levels remain consistent for a few weeks to a few months, electrolysis is complete. The amount of time this process takes depends on several variables, such as amount of salts in the environment the artifact was in and the size of the object.
The large cannons from the Revolutionary War shipwreck took five years to conserve. Smaller objects, such as nails might take 3 to 6 months.
The objects are then rinsed with hot water to remove residue from the electrolysis process. Once cleaned of this, objects are coated with corrosion inhibitor and sealed with marine oil to protect the surface.
Once dry, the object is ready to put on display!
All told, the Museum has conserved nearly 1,200 objects from over 200 concretions from the Revolutionary War shipwreck, preserving its story for generations to come. Mission Accomplished!
Again, thank you for joining the Virtual Museum today. We appreciate your continued interest and support! #LoveYourLighthouse and donate today, or take advantage of deep discount opportunities by visiting www.staugustinelighthouse.org.
For more on artifact conservation work, visit the St. AugustineLH YouTube channel for a Behind the Scenes conservation lab tour or search “conservation” on the Museum blog. And, be sure to visit our Virtual Museum webpage to see all our upcoming online opportunities including more Mission Accomplished Segments, Ask the Expert, Behind the Scenes Highlights and Facebook Live Sunsets and other events.