Shedding Light on the Invisible Details of the Capitol Campus

Photography: the word is derived from Greek and literally means "a representation by means of lines with light." Or, put in a more colloquial way, "drawing with light." The nature of the light that illuminates our world and makes the craft of photography possible, however, is an incredibly complicated subject that has been pondered by some of the greatest scientific minds throughout history.

What is visible, and invisible, to the eye?

One of the most notable discoveries about light is that it is both a particle (the photon) and a wave in the electromagnetic spectrum. This fundamental property of light allows us to describe light in terms of its wavelength. Within the spectrum of electromagnetic radiation, there is a narrow band of wavelengths to which our eyes are sensitive, corresponding to wavelengths between 400 to 700 nanometers. Light having these specific wavelengths and energies color our world; blue light has a shorter wavelength, while red light has a longer wavelength, the colors of which are a function of their wavelengths and the ways in which our eyes and brains perceive light.

The U.S. Botanic Garden Conservatory, and a saucer magnolia tree in bloom with the U.S. Capitol Dome in the background, photographed with an IR/UV monochrome modified camera.

Light with wavelengths near those to the visible spectrum are familiar to us and have a role in photography as well. Infrared (IR) light, for example, has longer wavelengths than visible light, ranging from 780 nanometers to 1 millimeter. This type of light is generally associated with objects that give off heat. Monochromatic, or black and white, photography can be sensitive to light in the near-infrared wavelengths of the electromagnetic spectrum. Specially modified camera sensors, certain types of film, and filters added to lenses can also increase the photographic sensitivity to infrared light. The resulting images made from infrared-sensitive photography tend to have a creative or surreal aesthetic, but have practical applications as well.

Additionally, ultraviolet light, which has a shorter wavelength than visible light, ranging from 10 to 400 nanometers, plays an important role in everyday life as well as photography. Ultraviolet (UV) light is most often associated as being the culprit of a sunburn after spending too much time at the pool. It is also a useful wavelength of light in photography that can reveal details invisible to the naked eye.

A Constantino Brumidi fresco in the U.S. Capitol photographed with standard flashes (left) and with UV flashes (right).

UV photography, in particular, has a long history in scientific and forensic image creation, and it is used by the AOC Photography and Technical Imaging Branch (PTIB) to help assess the conditions of artwork throughout the U.S. Capitol Building, and in the pursuit of scientific knowledge working alongside the United States Botanic Garden (USBG) staff.

How can this type of photography help with art preservation?

The vast majority of the PTIB's documentary mission within the agency is fulfilled by working in the visible light spectrum. However, there are many instances in which photography captured in the IR or UV wavelengths of light provide information or details important to project managers and historic preservationists responsible for the care and maintenance of the buildings and artwork under the purview of the AOC.

Certain molecules, when exposed to UV light, exhibit a glow known as ultraviolet fluorescence. This phenomenon occurs when the energetic UV light causes the electrons of a molecule to "jump" to a higher energy state. When the energy of the electrons return to a lower energy state, a photon, or the particle of light, is emitted from the molecule, causing it to glow. This type of fluorescence is commonplace in ordinary things such as certain naturally occurring minerals, the exoskeletons of many arthropods, the leaves and flowers of some plants, and, most importantly to the work of the PTIB, certain pigments in paints from the 19th and 20th centuries.

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Original paint (19th century) will fluoresce brightly, and areas that appear darker indicate the use of more modern paints.

By using powerful flash units or strobes fitted with special filters that block visible light but allow UV-A and a small portion of UV-B through (wavelengths between 300 and 400 nanometers), the PTIB has photographed many artworks throughout the U.S. Capitol Building to assess their conditions and aide in the preservation and conservation of these priceless works of art. Working alongside the AOC's curator and a team of historic preservationists and conservators, these images show, in vivid detail, where original paint remains, which brightly fluoresces, and where newer paint has been added by previous conservation efforts, which will appear as dark areas in the resulting image. UV photography can also reveal areas where certain varnishes, glues or binders have been used, as well as areas that have been damaged by fungal growth or other chemical contaminants.

The details revealed by the UV photography done by the PTIB play an important role in making decisions on how to best preserve the artwork throughout the many historic hallways and on the ceilings throughout the Capitol campus.

Does UV photography have other uses?

UV photography is not limited to only revealing details of artwork. The PTIB has supported the USBG in documenting the blooms of the Amorphophallus titanum by creating time-lapses, macro images of the flowers hidden down inside the bloom at the bottom of the tall central spadix, and UV images to determine if the plant exhibits fluorescence.

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Views of the A. titanum inflorescence photographed with standard flashes and then with UV flashes.

The USBG is involved in the conservation of the A. titanum, better known as the titan arum or corpse flower, which is an endangered plant indigenous to the tropical rainforests of Sumatra in Indonesia. This rare plant blooms for two to three days every two to three years, can reach a height of 9 feet or more, and smells of rotting flesh to attract pollinators. It is a captivating plant with a complex life cycle, and the study and conservation of this plant has important ecological considerations.

The images of A. titanum created with UV lighting are both visually fascinating and scientifically important. The spathe and spadix of A. titanum exhibited a strong fluorescence in purples and reds, indicating the presence of chlorophyl. The male and female flowers within the spadix also fluoresced strongly, with the tips of the female flowers glowing a contrasting white-blue, potentially helping to guide pollinators with eyes that are more sensitive than ours to UV light to the plant itself.

The Russell Senate Office Building's exterior photographed with an IR/UV monochrome modified camera; A Brumidi mural in the U.S. Capitol photographed with UV flashes.

The preservation and scientific applications of IR and UV photography are important aspects of the Architect of the Capitol's mission and the work done by the Photography and Technical Imaging Branch team. The images themselves, outside of the context of preservation or science, are quite intriguing to view on their own with the understanding that one is seeing what is otherwise hidden in plain sight.