Measuring fading of light-sensitive pigments

The recent analysis, by Raman spectroscopy, of a New Kingdom
Egyptian child's mummy case within our collection has identified the
use of orpiment as the yellow pigment for the face and (one
surviving) hand. Some fading of this light-sensitive pigment is
assumed to have already taken place. Since the mummy case is
intended for display, we would like to ensure it receives
appropriate lighting to control the risk of any subsequent fading.
We would be interested to hear from anyone who has undertaken, or is
aware of, any qualitative analysis of the fading of orpiment.

Following on from this, we are considering the purchase of a
portable spectrophotometer to monitor the mummy case, and other
objects and 2-dimensional artworks, to measure and examine fading
before it becomes visible to the eye. We would be interested in
hearing from anyone who has used a spectrophotometer for this
purpose, and particularly if and how they have determined the limits
of "acceptability", when using for example, and Delta E* as a
measure of difference between CIE L*a*b* values.

Rob Lewis
Assistant Conservator (Archaeology)
Cultural and Leisure Services
The Burrell Collection
2060 Pollokshaws Road
Glasgow G43 1AT
+44 141 2872592
Fax: +44 141 2872597


                                  ***
                  Conservation DistList Instance 19:29
                 Distributed: Tuesday, December 6, 2005
                       Message Id: cdl-19-29-022
                                  ***