Shedding light on faded artifacts: How to rediscover marks using UV light and phone apps
The artifacts that we find in the archaeological record can tell us so much about the past – but what happens when the decorative elements of an artifact are worn away? Luckily, technology has provided with potential tools to help us identify faded applied color labels on glass artifacts and overglaze designs on ceramic artifacts!
Let’s start with some background information about the types of artifacts discussed in this blog post. Applied color labels, or ACLs, have existed since CE 221 in China. Through time, there was a transition from manually created screen prints to a machine that could apply silkscreens to curved surfaces by the early 1930s (Lockhart and Brown 2019). Decorative overglaze ceramics typically have decorative designs painted on top of the glazed-ceramic surface (Florida Museum n.d.). Because of the way that these decorations are applied to their respective artifacts, they can wear off with time.
Recently, we cataloged a green glass bottle from the Spartan Village project that had only shadows left from the original ACL. We were able to identify the writing on the bottle by rotating the bottle under strong light. We identified it as a “Better Air” air deodorizer, a product that would have been used to help obliterate “obnoxious odors” in the home. While we were able to eventually identify this artifact and the words that would have been a part of the ACL, it took a few hours to identify the directions and additional information on the sides of the bottle.
Inspired by a thread in a historical archaeology listserv (yes, listservs still exist!), we decided to use a long-wave ultraviolet (UV) flashlight to identify the writing quicker (Walter et al. 2021) . UV light is electromagnetic radiation that can help us detect any features not be seen with just visible light (Pinter 2017). Because it is relatively affordable (and CAP already has UV flashlights in the lab to help identify uranium glass from previous excavations), this method could provide CAP fellows with a quick and effective way to find out what ACLs would have said before they wore off.
We found that the ACL shadows were, in fact, readable under the long-wave UV light. The angle of the UV flashlight was easy to manipulate too, allowing us to read the phrases on each green-glass fragment relatively easily. This process was simple and quick, providing future CAP fellows a quick and effective way to conduct future cataloging and research of glass artifacts with only ACL shadows present.
Glass artifacts are not the only ones that lose their designs over time. Archaeologists face similar identification issues with the fading of decorative overglaze ceramics. So we decided to test the UV flashlight on a whiteware ceramic with decorated overglaze.
While the outline of the design was roughly visible with the UV flashlight, it still was not clear. So we decided to use iDStretch, an app designed for iPhones to help enhance rock art and faint pictographs. This method uses decorrelation stretch, enhancing images that are hard to see with the human eye (Harman n.d.).
After trying out a few different color combinations, we were able to identify the shape of the leaf design that had worn off with time. By using iDStretch, we can more easily identify any shadows present from previous decorative overglaze designs.
Technology allows archaeologists to quickly identify any missing decorative aspects of artifacts in a quick timeframe. This lets us better describe and identify the artifacts that we come across, especially here on MSU’s campus!
The Florida Museum
No date “WHITEWARE, OVERGLAZED- type index.” Article, floridamuseum.ufl.edu. Available online, https://www.floridamuseum.ufl.edu/typeceramics/type/whiteware-overglazed/. Accessed November 2021.
Lockhart, Bill and Bob Brown
2019 “The Glamorous Applied Color Labels.” Article, sha.org. Available online, https://sha.org/bottle/pdffiles/ACLArticle2019.pdf. Accessed November 2021.
No date. “DStretch.” Article, dstretch.com. Available online, https://www.dstretch.com/. Accessed November 2021.
Walter, Susan, Denis Gojak, and Keith Doms (2021) “Fugitive Exposure” HistArch Listserv. November, 2021
2017 “Applying ultraviolet lighting in machine vision applications.” Article, vision-systems.com. Available online, https://www.vision-systems.com/cameras-accessories/article/16737654/applying-ultraviolet-lighting-in-machine-vision-applications. Accessed November 2021.