The discussion of the practical uses of UV light is great. I've used it
enthusiastically as a way of getting a new perspective on an artifact even
though it is ambiguous as an analytical tool.

Fluorescence is often controlled by factors other than the chemistry of the
artifact. For instance as glass decomposes it loses its transparency and
appears to fluoresce little or not at all. Also one's eyesight must be
conditioned to dark conditions to see weak fluorescence and to distinguish
colors well. Two observers often disagree on what color they're seeing
because color rendering decreases with light levels.

Most lamps give off a small amount of violet visible light. If the artifact
is reflective it can appear to be fluorescing violet. If a non-reflective,
non-fluorescing artifact is placed next to that artifact it will appear to
be black when in fact both artifacts are non-fluorescing.

Then there is the interplay between the power of the lamp, the sensitivity
of one's eyes and the particle size of the material being studied. This
becomes important when trying to distinguish fluorescing versus
non-fluorescing chemicals- like bone or limestone fragments in sediment. If
the particle is too small, the lamp too weak or the eyes too insensitive a
fluorescing material will be missed.

There is also the problem of differing colors coming from chemically
identical objects. Large optical calcite crystals usually fluoresce rose
colored under long and short wave light but sometimes they can fluoresce
distinctly orange under shortwave UV presumably due to minor impurities.

With that said I often pass artifacts under both my short and long wave
lamps just to see what I may have missed under visible light. Usually the
results are ambiguous or just highlight characteristics that are visible
under natural light but I'm sometimes led in directions of inquiry that I
wouldn't necessarily go in.

Since the power of the equipment can make a big difference I use the
strongest I could find:
Shortwave UV- Sprectroline Model R-51A (still available)
Longwave UV- Spectroline Model SB-100 (no longer available superceded by
SB-150)

The awkwardness of working under dark conditions is the worst practical
problem. Like observing the stars at night one sees far more after 30
minutes in the dark. When you group a large number of small artifacts for
dark condition observations at one time you have a good chance of misplacing
a bit here or there. While there are many solutions to this I like to
recycle my Stouffers microwaveable dishes as object trays. They are black
and don't fluoresce much (and they come with frozen meals in them!).

Both lamps require safety precautions, especially the shortwave lamp which
is quite powerful. One has to suit up with a full face mask and cover all
exposed skin. People who use UV goggles alone have been known to get
sunburned hands and from reflected shortwave UV.  And of course shortwave UV
in particular can damage the artifacts.
--

Dennis Piechota
Conservator
Fiske Center for Archaeological Research
University of Massachusetts at Boston
100 Morrissey Blvd.
Boston, MA 02125-3393
TEL: 617-287-6829
FAX: 617-287-6857