Ottawa - Canadian Association for Conservation

The Auto-fluorescence of Asian Lacquer
Marianne Webb, Senior Conservator, Decorative Arts
Royal Ontario Museum, Toronto ON
For several years conservators have noticed that Asian lacquer sometimes appears to fluoresce under
ultraviolet light. This study was undertaken to determine the circumstances of auto-fluorescence of
Asian lacquer. To begin, dozens of lacquer objects from the Royal Ontario Museum and the author’s
collection were examined. They all appeared to fluoresce. New sample boards were made and also
examined, which also fluoresced. It was determined that Asian lacquer always fluoresces, ranging in
colour from orange to muddy yellow, although due to the weak fluorescence of many objects it is not
always readily apparent. Several factors play an important role in observing the florescence, such as
quenching, ultraviolet lamp quality and the room environment.
Conservators studying lacquer observed that Asian lacquer fluorescence appears to increase
in intensity when the surface of the object has been previously damaged by exposure to light.
Experiments conducted on both fresh and aged samples of different types of lacquer demonstrate this
to be true. Asian lacquer exhibits a marked increase in fluorescence as well as a shift in colour from
orange toward yellow when exposed to UV and visible light for an extended period of time.
How is this knowledge useful to conservators? Experience has shown us that the degradation
products formed during light exposure are soluble in polar solvents. In fact this is why it is difficult
to safely clean lacquer without removing the top water soluble layer and possibly the decoration
along with it. It has been suggested that the increase in fluorescence could be a guide to cleaning,
as the fluorescence should return to its original state if the degradation products were removed.
Experiments were conducted on 12 objects with severe light damage. After cleaning with water, some
objects increased in fluorescence, some decreased and some remained the same. This indicates it is not
a good guide to surface changes during cleaning.
Although our knowledge of the chemistry of Asian lacquer auto-fluorescence is limited at the
moment, the phenomena can still be of some use in treatment. Because fluorescence increases with
light degradation, the colour and intensity observed can be used as a tool to determine the state of the
surface. When identifying Asian lacquer, it can be used to eliminate some look-alike materials and to
distinguish pigments. It is also useful to determine the treatment history of the object since objects
recoated with urushi or western varnishes are readily apparent.