Textile sample being placed in the spectroscopy detector for analysis. Important chemical information about samples is revealed by the spectrum produced through UV spectroscopy. Photo: Jeffrey Levin.

Ultraviolet/Visible Spectroscopy (UV/VIS) comprises a suite of multi-purposed tools that cross over and provide support functions for many types of studies. At one level, it is used to characterize the reflectance spectra of colored materials, such as pigments and dyes. Monitoring change in reflectance as a function of exposure to light, pollution, natural aging, or conservation treatments determines risks and stability of artifacts that incorporate those colorants. The reflectance spectrum also helps in characterizing a colorant when used with other methods to analyze artworks.

Beyond reflectance spectra of materials, these techniques can also examine the emission spectra of light sources themselves, and the transmission spectra of filters. Thus they offer additional methods to assist conservators and scientists estimate damage functions and preventative conservation techniques in exhibition lighting. We use six different instruments manufactured by Varian, Ocean Optics, and Control Development.

Applications:

UV/VIS studies of Andean dyes and colorants have yielded new information about trade and activities during the era and in the region where they were used.

By converting changes in visible reflectance spectra to human perceptible color space and then calculating differences in that color space, minute by minute, it is possible to focus a very narrow beam of intense light directly onto an artwork and to measure its light exposure sensitivity without knowing anything about the chemical make-up of the artifact, deriving that information with virtually no damage.

Emission and transmission spectra in the ultraviolet and visible light regions continues to be a good method to calculate the color rendering properties of new lighting technologies such as "white" LEDs when compared to incandescent or daylight. In addition, it measures the extent of protection from UV filters.

Color change has also let us to explore the benefits of alternative atmospheres for light-sensitive artifacts—nitrogen and argon typically being the two alternatives.

UV/VIS has also been used to investigate and to identify:

• dyestuffs in tapestries from the Gobelin and Savonnerie workshops of France;
• organic colorants on ancient Egyptian sarcophagi.

Further reading:

Wallert, Arie. "The Analysis of Dyestuffs on Historical Textiles from Mexico." In The Unbroken Thread: Conserving the Textile Traditions of Oaxaca, edited by Kathryn Klein. Getty Conservation Institute. 1997.

Wallert, Arie and Boytner, Ran. "Dyes from the Tumilaca and Chiribaya Cultures, South Coast of Peru." Journal of Archaeological Science 23 (1996): 853-861.

Wallert, Arie and Boytner, Ran. "Class, Control, and Power: The Anthropology of Textile Dyes at Pacatnamu." In South American Textile Traditions, edited by Margaret Young-Sanchez. Denver Art Museum.