The Secret Life of Artifacts: Exposed

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You’ve seen the conservators in the USS Monitor Center on the live web cam, but have you ever thought about what’s going on inside those tanks when the conservators aren’t covered with gunk?  My name is Leanna, and I’ve been interning with The Mariners’ Museum for two years.  I’m a junior at Christopher Newport University studying chemistry, and minoring in art history and leadership.   Chemistry plays an integral part of the conservation process. 

Last semester, I researched the process of conserving marine recovered copper artifacts, like many of those recovered from the USS Monitor wreckage. 

Hull of the USS Monitor

Copper is a very durable material, and can outlast other materials in the harsh marine environment.  Though copper is more corrosion resistant than iron, the high concentration of water and salts (like chlorides) causes accelerated deterioration. 

Copper alloy butt plate from a rifle

Ensuring these salts are removed is especially important, as salts can lead to a condition known as “bronze disease”, a condition that can destroy an entire artifact.  When artifacts are brought out of the ocean, they must be kept wet in order to prevent chlorides from being trapped.  Deconcretion, or the process of removing foreign sediment from artifact, is an important first step as it reveals more of the artifact’s surface.

Conservator deconcreting artifact with a pneumatic scribe

Not only does this give a more accurate representation of the item, but it also allows a greater surface are for chlorides to be removed.  A variety of solutions are used to facilitate chloride removal, including deionized water and sodium sesquicarbonate.  Additionally, a process known as electrolysis helps ­remove salts from the artifacts. 

http://www.marinersmuseum.org/sites/default/files/electrolyticreduction.swf

The negative charge of the electric current helps to repel the negatively charged chloride ions (Cl-) from the artifact and into solution.  Chloride levels are monitored using a method known as ion chromatography, testing the solution the artifact is kept in. 

Ion chromotography system in action

Desalination (the removal of salts) is complete when the chloride levels remain low.  Electrolsis also reduces copper corrosion products back to more stable copper corrosion by the addition of electrons.  Following desalination, the artifact must be dried, as water can re-facilitate corrosion.  This is typically done either by setting the artifact under a fume hood in the open air, or placing it in a solvent such as alcohol that helps to remove the water.  A chemical known as benzotriazole (BTA) is then applied, and forms a barrier between the artifact and the surrounding environment.  An additional coating is applied for extra protection and can cause the artifact to either look matte (dull) or gloss (shiny) based on the coating used and desired final appearance.

Note the unique patina on the surface of this artifact

I’ll be writing another blog soon that goes into detail regarding the specific chemical reactions.  If you have any questions, I look forward to hearing from you in the comments section!