Topics Related to Conservation Highlights
When we think of glass today, we mostly think of something like clear, flat window glass – impervious to water and unchanging across the years. Sure, if someone hits a baseball through it the window will break, but there’s not much you can do to chemically damage the glass itself… right?Glass is made of three major components: silica (from sand), a flux (potassium or sodium compounds), and a stabilizer (calcium, magnesium, and lead compounds).
Salt is bad for most things; it breaks apart glass and ceramics, corrodes copper alloys, and contributes to the decay of organic materials. It is especially bad for iron artifacts and, after 300 years in the ocean, the iron from Queen Anne’s Revenge is very, very salty.
After 300 years on the sea bed, the condition of objects is highly variable. When objects are in very good condition it’s easy to tell what they are made of, but when things have rusted, rotted, and decayed away that gets a lot harder. With extremely damaged objects conservators run into one fundamental problem: how do you fix something if you don’t know what it’s made of?
After resting on the ocean floor for 300 years, it is only natural that the artifacts would become salty. The salt in seawater is soluble (dissolved in a liquid, such as water) which allows it to enter most of the materials found on the site. Salt enters the artifact through the process of osmosis; a concentrated solution (seawater) goes through a membrane (the surface of the artifact) to a less concentrated solution (inside the artifact) to balance the amount of salt on both sides.
Not only do we raise large, immediately recognizable objects from QAR such as cannons and anchors, but we are also constantly on the search for minute remnants of shipboard life.
In following along on our adventures in conservation, you may have learned a new term often heard in the lab: concretion. As described in previous entries, concretions can contain a wealth of artifacts, made of many different materials. Corrosion is the driving force behind the development of concretion on iron and the subsequent envelopment of other artifacts nearby. We find a lot of iron on Queen Anne’s Revenge, thus a lot of corrosion, and in turn, a LOT of concretion.
The bulk of artifacts recovered from maritime environments, the Queen Anne’s Revenge included, are found in a concreted state, which is a cement like formation over the artifact that must be removed before further treatment can continue. After the concretion is initially assessed by the conservator via visual review and x-ray, the conservator can then begin the concretion removal process.
The Queen Anne's Revenge has been hidden off the coast of North Carolina for almost 300 years. Those years have not been kind, slowly eroding away the organic components of the ship and encasing the metals of the ship in concretion. The sea is not particular in its encasement; like the celebrated Blob of monster movies, it not only encases the metals but anything next to it as well. Concretions can be small enough to fit in your hand, or large enough to encase a cannon – or an anchor. The Lab in Greenville has literally thousands of concretions from the site.
Archaeological conservation is the applied science of preserving artifacts. According to the Society for Historical Archaeology, “Conservators prevent objects from deterioration through careful examination, documentation, analysis, preservation, restoration and preventive care.” In our case, these archaeological materials come from a submerged saltwater site, which adds a level of complication to the work needed to protect the artifacts for future study and interpretation.