Conservators have many tools to clean artifacts at the Maryland Archaeological Conservation Lab. A new tool employed in the lab this summer can be sourced here on the grounds of the Jefferson Patterson Park and Museum (JPPM): thorns!

Thorns are ideal for cleaning soft archaeological artifacts that are easily scratched, like gold and gilt surfaces (Auffret and Nikolaus 2019). They're also sharper than other tools used around the MAC Lab, like bamboo skewers and porcupine quills, so they’re great for getting into hard-to-reach places. Thorns are harvested, allowed to dry and harden, and mounted in a pin vice to make them a handheld tool to use under the microscope.

Thorns were most notably used by the UK conservation team that cleaned the Staffordshire Hoard, a collection of 4,000 7th century gold and garnet cloisonné and filigree artifacts excavated from a potato field in England. This team selected several types of plants based on what was available in England (The Institute of Conservation 2015). The thorny plants used by the Staffordshire Hoard team aren’t available in Maryland. With the help of Lindsay Hollister, JPPM’s horticulturalist, conservators selected two species that could be sourced here at the park.

Black locust trees (Robinia pseudoacacia) are native to the western Maryland mountains but have since spread to most of the state (Ujeta-Esteban and Tayviah n.d.). They are fast growing trees that like sunny, disturbed areas, and thorns are more common on new growth (Huntley 1990). At JPPM, black locusts are found along field edges, and low hanging branches are often in the way of our mowing crews.

Common greenbrier (Smilax rotundifolia) is a climbing vine with glossy green leaves native to the Eastern US including Maryland (JPPM n.d.). Individual vines grow into thickets that provide cover for birds and small mammals. Greenbrier thorns have black tips. At JPPM, greenbrier is common along field edges and occurs in patches in the woods.

Thorns recently helped in the cleaning of a historic copper alloy spur. A chalky white substance was embedded in microscopic divots across the spur. This may be an old coating or old polishing compound and needed to be removed. While a scalpel tip could fit in most of the divots, copper alloy is softer than steel and could be easily scratched. Both a bamboo skewer and porcupine quill were too large to fit into most of the divots, so a black locust thorn came to the rescue.

References Cited

Auffret, Stéphanie, and Sydney Beall Nikolaus

2019    Cleaning of Wooden Gilded Surfaces: An Experts Meeting Organized by the Getty Conservation Institute. Los Angeles: Getty Conservation Institute. http://hdl.handle.net/10020/gci_pubs/gilded_surfaces.

Huntley, J.C.

1990    "Robinia Pseudoacacia L." In Silvics of North America: Volume 2. Hardwoods, edited by Russell M. Burns and Barbara H. Honkala. Southern Research Station, USDA Forest Service, 1990. https://srs.fs.usda.gov/pubs/misc/ag_654/volume_2/robinia/pseudoacacia.htm.

The Institute of Conservation

2023    "ICON News: The Magazine of the Institute of Conservation," May 2015. Accessed August 1, 2023. https://www.icon.org.uk/resource/icon-news-58-may-2015-pdf.html.

Jefferson Patterson Park and Museum (JPPM), Maryland Department of Planning

2023    "Common Greenbrier." Accessed August 17, 2023. https://jefpat.maryland.gov/Pages/education/plants/common-greenbrier.aspx.

Ujeta-Estaban, K., and Tayviah V.

2023    "Black Locust." Glen Arboretum, Towson University. Accessed August 17, 2023. https://wp.towson.edu/glenarboretum/home/black-locust/.