Archaeological Conservation

The main goal of archaeological conservation is to stabilize artifacts for long-term preservation. Depending on the condition of the artifact, this can involve chemical treatments, mechanical cleaning, or simply storage in the proper environment.

Page updated on Jul 17, 2020 at 11:53 AM

Conservation of an Historic Ship and Warehouse

220 S Union Ship (13). Courtesy, Anna Frame.

The historic ship discovered on Alexandria’s waterfront in 2016 needs your help!  Early Alexandrians sunk this vessel on the Potomac mudflats over 200 years ago. Archaeologists unearthed the ship, temporarily saving it from destruction. 

After excavating and disassembling the ship, it was transported to a facility here in the city and placed into two large tanks of water to begin the long conservation process. It was later sent to Texas, where researchers from the Conservation Research Laboratory at Texas A&M continue conservation of the ship.

Remains of the 1755 warehouse found at the same site are also undergoing professional conservation at the Maryland Archaeological Conservation Laboratory. This is a multi-year project.

We need your help to ensure the preservation of the fragile wood timbers of the ship for future generations to study and appreciate. Please make a generous donation to the Save Our Ship Conservation Fund

Conservation: Storeroom New imageConservation Survey

Alexandria Archaeology conducted a complete conservation survey of all of its collections in 1989, with funding from the Institute for Museum Services (IMS, now IMLS). The survey was done as part of the process to create a new storage facility. The old storage facility was overcrowded and lacked climate control, causing damage to the boxes.

The conservator, Carol Snow, evaluated storage conditions and made recommendations for the new storage facility, which was built in 1991. She made recommendations for climate control; and for materials for construction, shelving, and packaging that would not off-gas and cause harmful reactions with the artifacts. She also worked with a team to examine each of 3,100 boxes of artifacts, and made recommendations for treatment. Another IMS grant funded conservation treatment for the higher priority artifacts, those that were unstable and would continue to deteriorate without treatment. All artifacts were moved to the new climate-controlled facility and rehoused in recommended materials.

Creamware punch bowl

Conservation and the Urban Renewal Project

Many artifacts from the Urban Renewal Project on the 300 and 400 blocks of King Street were conserved or restored in the 1960s and 1970s. These excavations and the conservation work were conducted by Richard Muzzerole under the auspices of the Smithsonian’s Museum of History and Technology (now the Museum of American History). The conservation work included stabilizing wood, leather and metal objects, as well as restoring ceramic and glass vessels for exhibit purposes, using Plaster-of-Paris infill. Although conservation standards have evolved over the decades, most of these treatments held up very well over time. During the 1989 conservation survey, the conservator reviewed the earlier methods used, and retreated a few objects that had become unstable.

Conservation: Musket Part imageConservation of the Musket in the Privy

Alexandria Archaeology discovered the  Wickham Musket during excavations at the Alexandria Courthouse site in 1978. The gun, cocked and loaded, was thrown into the backyard privy of a house at 106 South Saint Asaph Street some time in the 1860s. The musket was manufactured by Marine T. Wickham between 1822 and 1834. Wickham, a former Master Armorer at the Harper's Ferry National Armory, produced muskets under contract for the government at his Philadelphia factory.

The musket was found in the privy with its muzzle down and broken at the wrist. The waterlogged wood was well preserved, but stained black from the privy. The metal components were badly corroded. An undamaged flint and a leather cushion were still clamped in the jaws of the hammer, which was frozen in the firing position. Priming powder was still in the pan, and x-rays revealed a .69 caliber musket ball with wadding and a powder charge in the barrel. However, the mainspring, which snapped the hammer and flint against the frizzen, was broken.

Volunteer Jan Herman worked with conservator Lynn Arden for a year and a half to preserve and restore the Wickham musket. The gun was carefully taken apart so that wood and metal could be treated separately. The musket was X-rayed, revealing the ball and powder charge. The powder was tested in a laboratory, but was no longer volatile. X-rays were also used to examine the condition of the metal. As the iron and steel components were basically sound, the surface corrosion was removed using an electrolytic tank. Treating the wood was a more time consuming process. The gun was cleansed in successive water baths for six weeks to remove dirt and impurities. Then the water, which filled the cells of the wood, was gradually replaced with a waxy preservative in a process that took six months. This enabled the wood to retain its shape. The musket was carefully reassembled with replacement parts of gray painted wood and wax, clearly distinguishable from the original wood and metal.

Conservation: Lee Street Shoe imageConservation on a Water-logged Site

If you had visited the Alexandria Archaeology Museum in the summer of 1998, you would have seen conservator Lisa Young, her assistant Christen Runge, and Alexandria Archaeology volunteers treating artifacts that were excavated from the  Lee Street Site. The site included a Civil War era U.S. Military Hospital complex at the corner of North Lee and Queen streets. Most of the artifacts in need of conservation came from a privy, or out-house, where the artifacts remained wet throughout 130 years of burial. The wet environment, due to the depth of the privy and its location in the tidal flats of the Potomac River, allowed an extraordinary degree of preservation. A wonderful assortment of the artifacts from this site are now on display in the Alexandria Archaeology Museum, including leather shoes and fragments of harnesses and haversacks, wooden tools and brushes, and metal bullets, buttons and lamps.

Preservation of the artifacts is an obligation of those excavating any site, and wet sites always have higher conservation needs. In preparation for the conservation project, a conservation survey was conducted in which all of the objects from the Civil War privy were examined and several hundred of the most significant and unstable objects were selected for treatment. Many artifacts are on display in the Museum.

Waterlogged Wood:  Waterlogged wooden artifacts retain their shape as long as they remain wet. If allowed to dry without conservation, wood will warp, shrink and crack. The conservation team first cleaned the wood, and then soaked it for several months in a liquid wax called Polyethylene Glycol (PEG). The PEG filled the wood cells and helped the object to keep its shape. The artifacts were then stored in a freezer and later freeze-dried, just like coffee or space-food.

Water-logged Leather: Leather shoes and straps from the privy were in excellent condition--still flexible and supple--but would have stiffened and cracked if allowed to dry without treatment. Conservation treatment involved removal of water from the leather cells and introduction of an inert wax consolidant that holds the shape of the object.

Metal Artifacts: Lead musket balls, brass buttons and buckles, copper coins, a tin cup and other metal objects were heavily corroded after 130 years of burial in the damp earth. They had to be carefully cleaned and stabilized to prevent further deterioration. The artifacts were mechanically cleaned with a scalpel and fiberglass brush or by a technique called air-abrasion, in which powdered walnut shells or tiny glass beads are directed at the object. The artifacts are then coated to protect the surface. The copper and brass objects from the site are unusually bright and shiny after conservation, due to a protective layer of black sulfide corrosion that was found underneath the more familiar green copper carbonate corrosion.

Conservation: Wagon Wheel MAC Lab imageConservation of a Wagon Wheel

This three-foot tall wooden wheel with metal rim was found with partial remains of a wagon near the ruins of a barn in West End Village, at the  site of the US Patent and Trademark Office on Duke Street. The site was excavated by Goodwin & Associates in the spring of 2002. The wagon, possibly a one-horse agricultural cart, dates to the latter half of the 19th century, and is a reminder of the agricultural community that still existed in Alexandria in the late 19th and early 20th century. Along with artifacts in our collection from the Virginia Glass Factory and the beer cellar which underlies Duke Street, the wagon wheel presents a picture of the West End at the turn of the century, and of a Duke Street which is very different than today.

Prior to conservation, the wheel was kept damp (as it was found) at the Goodwin lab in Frederick, Maryland. The wheel was transferred to the Maryland Archaeological Conservation Laboratory at Jefferson Patterson Park for treatment. Examination and assessment of the wheel was conducted by Rececca Cashman under the supervision of Howard Wellman. During examination, the wheel was kept in a tank filled with purified water. Detailed investigation included x-ray to assess condition of the metal components, metal sampling to detect chloride content, and thin-section species identification of the wood. The wheel was further documented with sketches and photography. Dirt and corrosion were removed with mechanical cleaning, and the iron elements were desalinated using electrolytic reduction. The wood was stabilized using polyethylene glycol (PEG) to displace water and provide bulking stability after drying. The object was then freeze-dried – the MAC Lab has one of the few facilities in the country with a freeze-dryer large enough for an object of this size. The surfaces were stabilized with a coating, and the wheel was returned to Alexandria Archaeology where it is stored in a stable climate-controlled environment when not on exhibition.

Conservation: Civil War trunk plateConservation of Civil War Artifacts

Another museum conservation project was the conservation of artifacts from several Civil War camp sites. The metal artifacts recovered from these sites included lead ammunition, iron rifle parts, and copper alloy accouterments such as cartridge box plates, saddle shields, shoulder scales, buttons, knapsack hooks and hat horns.

Some artifacts could be protected for the future with proper packaging. While most artifacts are kept in a stable environment of around 45-50% relative humidity, metals must be kept in a much drier environment to prevent corrosion. Micro-environments, consisting of air-tight polyethylene food-storage boxes and a packet of a desiccating agent called silica gel, are created to maintain a dry environment for the metals. The silica gel absorbs moisture in the air, and indicating crystals turn color to indicate when the silica gel should be changed to maintain the dry conditions. Other artifacts needed mechanical cleaning and coating to preserve them, and to make them stable enough to be used in exhibitions.