ConserveO Gram

December 2000 Number 1/9

The Use Of Ultraviolet Induced Visible-Fluorescence In The

Examination Of Museum Objects, Part I
A commonly available ultraviolet lamp can be All forms of electromagnetic radiation are
used as a tool to aid in the examination of classified according to wavelength.
museum objects. Ultraviolet radiation is Wavelengths are measured in nanometers (nm).
invisible to the naked eye. However, when it is A nanometer is one billionth of a meter.
emitted from an ultraviolet lamp and directed at
the surface of an object, it is often transformed
into visible colors. These colors are known as
ultraviolet-induced visible fluorescence. In
conjunction with other examination techniques,
observation of this fluorescence can help
collections managers to answer questions
regarding the identification of materials and the
condition of artifacts. In turn, this information
may aid in making decisions regarding issues
such as handling, storing, and cataloging of
collections. (See Conserve O Gram 1/10, The
Use of Ultraviolet Induced Visible-Fluorescence
Figure 1. The Electromagnetic Radiation Spectrum.
in the Examination of Museum Objects, Part II
for more information.)
Visible light is the only portion of the
electromagnetic spectrum that can be seen by the
Much effort has been made in recent years to
human eye. Visible light radiates at
limit the exposure of museum objects to
wavelengths between 400 and 700 nm. UV
ultraviolet radiation. Over time, ultraviolet from
radiates at shorter wavelengths, between visible
both artificial sources and natural sunlight has a
light and X-rays. (See Figure 1.)
cumulative effect on materials and can cause
damage and fading of items such as textiles,
The ultraviolet portion of the electromagnetic
paper, and other organic objects. The amount of
spectrum can be further broken down into the
ultraviolet radiation absorbed by an object
following regions:
during a brief examination using an ultraviolet
lamp is very small. If a pertinent question about
the object can be answered using ultraviolet- • UV-A, commonly known as long-wave UV,
induced visible fluorescence, the use of this near-ultraviolet, black light, or Wood’s light
technique may be considered acceptable. (between 320 and 400 nm)

The Electromagnetic Radiation Spectrum • UV-B, also known as medium-wave UV

(between 280 and 320 nm)
Ultraviolet (UV) radiation, along with visible • UV-C, often referred to as short-wave, far-
light, infrared, radio waves, x-rays, and the less ultraviolet, or germicidal UV (between 180
familiar gamma rays and cosmic rays, is a form and 280 nm)
of electromagnetic radiation. (See Figure 1.)
National Park Service Conserve O Gram 1/9

Of these regions, UV-A (long-wave) and UV-C curtains and shades can be used on windows,
(short-wave) are the most useful in examining and sand snakes can be placed at door
museum objects. Commercially made long- thresholds. With overhead lights or a task light
wave UV lamps and short-wave UV lamps are turned on, place the object securely on a table or
readily available from various vendors. easel. Use weights as necessary to secure the
object in place. Plug in the UV lamp (unless it
Ultraviolet-Induced Visible Fluorescence is battery-operated), and take care that the cord
is not tangled and that it cannot accidentally
Many natural and synthetic materials transform knock over the object while it is moved in the
the ultraviolet radiation that strikes them into dark.
longer wavelength visible radiation or visible
light. This phenomenon is referred to as Turn off the room lights and let your eyes adapt
ultraviolet-induced visible fluorescence. When to the darkness for a minute or two. Observe the
UV radiation is absorbed by a reactive material, object under UV radiation. Areas that appear
electrons are pushed temporarily into a higher totally dark are not fluorescent. Some non-
energy state. The absorbed radiant energy is fluorescent surfaces (e.g. metals) may reflect
released as these electrons return to their normal some of the small amount of visible light that is
state. Much of this released radiant energy, or emitted from the UV lamp. Be careful not to
fluorescence, has wavelengths in the visible light confuse this reflection with fluorescence. Turn
region and thus can be observed. Whether on a dim task light as necessary for a frame of
fluorescence occurs at all, as well as the color, or reference or to take notes.
specific wavelength of the fluorescence, depends
on the material under illumination and the Never attempt to move or reposition the object,
wavelength of the UV radiation that is used. or to clean, test, or otherwise alter an object
under UV illumination. These activities should
Personal Safety be undertaken only when the room or task lights
are turned on. The UV lamp should only be
Long-term exposure to UV radiation can lead to used to examine an object.
serious and irreversible vision problems,
including cataracts, glaucoma, and macular Remember, the colors of the observed
degeneration. It is recommended that protective fluorescence will depend on the material and the
eyewear be worn at all times when working with wavelength of the UV light that is being used. It
a UV lamp. It is especially important when is important to use a UV lamp with the
working with lamps emitting appropriate wavelength for the question(s) at
UV-C, or short-wave UV, which is most hand. For example, many adhesives used in
damaging to the eyes. Safety glasses of coating and repairing objects fluoresce under
polycarbonate and other plastics, made long-wave UV and do not fluoresce at all under
specifically to filter UV light, are commonly short-wave UV. Therefore, a long-wave UV
available. Glasses that fit over prescription
lenses can also be purchased. lamp should be used to determine if an object,
such as a ceramic, has been broken and repaired.
On the other hand, many mineral specimens
Examining Art and Artifacts fluoresce characteristic colors under short-wave
UV and do not fluoresce under long-wave UV.
Therefore, a short-wave UV lamp should be
To view an object with a UV lamp, choose a
used to aid in classifying and cataloging this
dark room, such as a storage or photography
type of collection. (See Conserve O Gram 1/10,
area. Fluorescence is not very bright, so as
The Use of Ultraviolet Induced Visible-
much as possible, eliminate sources of stray
Fluorescence in the Examination of Museum
light through windows and doors. Block-out

2 The Use of Ultraviolet Induced Visible-Fluorescence, Part I

Conserve O Gram 1/9 National Park Service

Objects, Part II, for further information and for Fine Arts 2 (1934): 153-157.
guidelines in choosing a UV lamp.)
Marsh, Moreton. “UV or not UV.” Maine
As with any examination or analytical technique, Antique Digest, January 1980, 1C-6C.
avoid drawing conclusions about an object based
on ultraviolet-induced visible fluorescence Rorimer, J.J. Ultra-Violet Rays and Their Use
alone. Instead, it is best to make observations in the Examination of Works of Art. New York:
and to use these in conjunction with other Metropolitan Museum of Art, 1931.
evidence about the object. This caveat is
especially true with regard to issues of Warren, Thomas S., Sterling Gleason, Richard
authenticity. C. Bostwick, and E. Verbeek. Ultraviolet Light
and Fluorescent Minerals: Understanding,
Acknowledgments Collecting and Displaying Fluorescent
Minerals. Baldwin Park, CA: Gem Guides
The author would like to thank Dan Kushel, Art Book Co., 1999.
Conservation Department, Buffalo State
College, for his valuable contribution to this
Conserve O Gram.

The author would also like to thank Spectronics Martha Simpson Grant
Corporation of Westbury, New York, for Objects Conservator
permission to reproduce the diagram of the Austin, Texas
electromagnetic radiation spectrum illustrated in
Figure 1.

References

De la Rie, E. Rene, “Fluorescence of Paint and

Varnish Layers,” Parts I, II, III. Studies in
Conservation 27, no. 1: 1-7; no 2: 65-69; no. 3:
102-108.

Eastman Kodak Company. Ultraviolet and

Fluorescence Photography, Publication #M-27.
Rochester: Eastman Kodak Company, 1969.

Lyon, R.A. “Ultra-violet Rays as Aids to

Restorers.” Technical Studies in the Field of

The Conserve O Gram series is published as a reference on collections The series is distributed to all NPS units and is available to non-NPS
management and curatorial issues. Mention of a product, a institutions and interested individuals by subscription through the
manufacturer, or a supplier by name in this publication does not Superintendent of Documents, U.S. Government Printing Office,
constitute an endorsement of that product or supplier by the National Washington, DC 20402; FAX (202) 512-2250. For further information and
Park Service. Sources named are not all inclusive. It is suggested that guidance concerning any of the topics or procedures addressed in the series,
readers also seek alternative product and vendor information in order contact NPS Museum Management Program, 1849 C Street NW (NC 230),
to assess the full range of available supplies and equipment. Washington, DC 20240; (202) 343-8142.

The Use of Ultraviolet Induced Visible-Fluorescence, Part I 3