Invisible ink

On behalf of a colleague Nicole Hayes
<nicole [at] ica-artconservation__org> writes

>    I was at a symposium recently and one of the speakers
>    recommended rare books be marked with invisible ink (visible
>    under UV light) so as to be traceable.  He assured the audience
>    that these inks were archival, and called them "Identi-kits."

Some of the commercial products I looked at were specifically
designed for marking property permanently. It seems like a very
unobtrusive method of marking, capable of giving a false confidence
to the owner. The main limitation for conservation application is
that exposure to light can cause the inks to stop fluorescing under
UV light. Some of the basic experiments I performed for this
research revealed that the optical brighteners in the ink could be
almost entirely exhausted if exposed to sunlight for one day.  So if
a marked item was exposed to enough UV exciting light, it would look
clean for resale. My testing did not address extended artificial
aging to examine possible yellowing of the ink and substrate over
time, but there is published research in optical brightening agents
(OBA) and Dayglow paints showing the marks go a dull brown when the
UV excitation is exhausted. So there is no long-term guarantee that
these markings would stay invisible.

Of course, we would presume that the light exposure of a page in a
volume housed at a cultural institution would be far less than the
exposure I mentioned above. Nevertheless, I think it's important to
consider non-ideal situations when we are talking about theft, since
"recovery" only happens after the item has been removed from our
care and control. Regardless of the chosen marking method, a
determined and informed thief could easily deface these markings and
obscure the book's provenance. Personally, I do not think invisible
ink has many advantages over other, more traditional, marking
methods such as stamping, embossing, and plating.

Sonja P. Reid


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                  Conservation DistList Instance 23:22
               Distributed: Wednesday, December 23, 2009
                       Message Id: cdl-23-22-001
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