Monitoring colour change for objects on display

At Imperial War Museums (IWM) we are preparing objects for our First
World War galleries opening next year and would like to develop a
practical process to monitor changes in condition of objects whilst
they are on display.  The display incorporates a wide variety of
media on paper with varying light sensitivity and we want to be able
to monitor colour change for some of these.

In the past we have generally used facsimile objects for long term
display of paper objects, however we are keen to display 'real'
objects wherever possible.  Therefore, we have developed a risk
matrix for light exposure that incorporates the estimated light
sensitivity of objects, their significance and the rate of change
acceptable to us.  This is used to inform our facsimile and rotation
policy.  To assist in validating this approach and due to the
unknown nature of many of the inks and pigments, we need to be able
to monitor colour change in a straightforward but quantifiable way.
We would do this as part of a scheduled condition checking programme
to determine if the rate of colour change is faster (or slower) than
we have anticipated and our rotation or facsimile programme needs to
be adjusted accordingly.

We are interested in finding out whether anyone has experience of
using a colorimeter or spectrophotometer as part of a
condition-checking procedure or can recommend any other successful
method to monitor colour change over the medium to long term.

Of particular interest to us would be:

    Ability to monitor colour change of the order of 1 just
    noticeable fade/change (c. 1-2 Delta E)

    Repeatability - especially as we may have to borrow or hire
    equipment for each condition checking cycle

    Colorimeter or spectrophotometer - cost and ease of use

    Is testing in-situ possible?

    Sample spot size--for much of the material we are concerned with
    the fading of handwritten text

Note that we have also been considering micro-fading as part of the
initial assessment.

Fiona McLees
Paper Conservator
Imperial War Museum, London


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                  Conservation DistList Instance 27:2
                  Distributed: Thursday, June 13, 2013
                        Message Id: cdl-27-2-017
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