The effects of oil contamination on cultural resources will continue to be a challenge to the Gulf Coast region for years to come. NCPTT is meeting this challenge with technical research support for state and federal land managers, and for the public.
|Jason Church collects samples of oil-saturated sand northwest of the outer wall of Fort Livingston, Grand Terre Island. The dark patches on the sand in the foreground are areas where "mousse" that washed up on the beach melted into the sand. The structure's walls are tabby, faced with brick. Note the high tide line indicated by the dark oil staining on the brick and the tabby in the background.|
At the request of the Louisiana Office of State Parks, NCPTT researchers visited Fort Livingston to document oiling, sample crude oil from the rupture, and provide guidance for cleaning up the site. The crude oil samples will be used in future research projects.
The National Center provided advice for containing the oil away from sensitive historic structures to the National Park Service’s Gulf Islands National Seashore and other locations. NCPTT also partnered with Louisiana State University to evaluate and test rapid documentation methods in Grand Isle, La., and further north along Bayou Lafourche.
Early in the response efforts, NCPTT coordinated with other federal agencies to develop protocols and best practices to document and protect cultural resources. Additional efforts included providing public maps showing location of historic structures and sites in relation to the oil spill.
NCPTT continues to participate in regular NPS-organized conference calls with federal agencies about cultural resources response in the affected area. More recently, the National Center developed general guidance for removal of crude oil contamination from historic structures. Fact sheets are planned for removal of crude oil from archeological objects.
A new research project is under development to test surface washing agents on historic materials. Results of this research will help responders select appropriate cleaners from those listed on the Environmental Protection Agency National Contingency Plan Product Schedule.
New Study Expands Research for Removing Crude Oil from Historic Brick
by Katherine Langdon
Since the summer of 2010, NCPTT has been actively researching the removal of crude oil from objects and sites of cultural significance, such as Fort Livingston. This 19th century coastal fort on Grand Terre Island, Louisiana, was badly contaminated by the 2010 Deepwater Horizon oil spill. Our scientists visited the site twice last year to perform some preliminary studies on oil removal, and this summer I have been continuing with research on removing weathered oil from historic brick. The goal is to find a cleaning method that effectively strips the oil from the masonry without causing additional harm to either the structure or the environment.
Historic brick is much more fragile than most modern brick because it was fired to a lower peak temperature, leaving it softer, more porous, and more prone to environmental damage than higher-fired, vitrified brick. Crude oil presents a triple threat to historic brick because it mars the appearance, traps moisture (encouraging mold and salt crystal growth), and contains acidic chemicals (and so will corrode lime mortar, which is basic). Thus it is important to find a way to remove the oil quickly and efficiently while keeping the following goals in mind: the cleaning method must not be acidic (i.e., it must have a pH of 7.0 or higher), must not leave a water-impermeable residue, and must not abrade or discolor the brick.
|Katherine Langdon at Fort Livingston testing cleaning methods on oil-contaminated bricks, July 2011.|
|Scientists removing a clay poultice from a test brick-- this product seems to be working!|
In the lab I am using historic bricks from Atlanta, Texas, which are similar to the bricks at Fort Livingston. These samples are soaked in salt water, coated in crude oil, and put through accelerated weathering to simulate the conditions of historic bricks along the coast. This week, the samples came out of the QUV accelerated weathering tester. I will begin the cleaning stage of the experiment to compare many products that meet our requirements. Recently we tested many of them on-site at Fort Livingston for comparison to the lab samples, and some of them did quite well! The final research and findings will be published on the NCPTT website in a couple of months.
All ‘dem Bones: Cleaning Oil from Archeological Bone.
|Bone samples to be tested.|
The effects of oil spills in terrestrial and marine environments are a growing concern globally, but understanding and mitigating these effects is a top priority at NCPTT.
Bone is a material with which most of us are familiar. Bone is made up of a combination of proteins: minerals like calcium and potassium: and vitamins. Bones are primarily made of “osseous tissue.” Two types of osseous tissue are in bone, compact and spongy. Compact osseous tissue forms the hard, smooth surface that most people imagine when thinking of bone. Spongy osseous tissue is the same material, but softer and fills the hollow interior.
Shell, like bone, acts as protective outer layer or exoskeleton created by a marine organism. The shells you find washed up on the beach are the remains of the organism after it has died. Shells are typically composed of calcite, calcium carbonate and conchiolin.
Many cultures, present and past, have utilized bone and shell for tools, weapons and ornamentation but what happens when these materials come into contact with crude oil? How do we remove the oil? Can we restore these artifacts if they do come into contact with crude oil? And once cleaned how will this affect their future curation?
That is what we here at NCPTT are trying to find out. Using unprovienced archaeological samples, we are experimenting to find the best method for removing oil from artifacts of bone and shell. The initial stages of the study included a thorough literature review, experiment design and selection of surface washing agents and/or surfactants.
|Erin White takes color measurements of bone samples before they are treated.|
The experiment will start with documenting the physical condition of the samples prior to applying oil. This involves analyzing the color with the Minolta CR 400 Colorimeter, recording the mass, etc. Once the oil is applied, half of the samples will be cleaned. The other half of the will be placed in a QUV artificial weathering chamber, for approximately 800 hours to simulate real world conditions. This will simulate artifacts that have been exposed to oil and allowed to weather over time before cleaning. Once this stage is complete, we will test each of the selected cleaners on the samples. At the end of the study, we hope to have evidence for best method for removing oil from bone and shell artifacts.
Special Thanks to the Charleston Museum for the donation of bone and to the Southeast Archeological Center for the donation of shell for the project.