UV-Visible spectra of iron gall ink

I have two non-conservation colleagues who are trying to enhance the
image of mechanically abraded "faded" iron gall ink on parchment.
They are imaging at very high resolution (800 ppi at 48-bit) using a
BetterLight scanning back, a 120 mm Schneider Apo-Symmar lens, with
full spectrum fluorescent lights.

They have tried removing the infrared filter with no improvement in
contrast between ink and parchment.  That is, the IR filter used on
the camera lens to yield only the "visible" image.

The only minor enhancement they have be able to achieve is using UV
light, with no filtering.  The abraded ink areas show a blue-green
fluorescence, while the parchment alone shows the traditional modest
green fluorescence.

They are seeking a UV-Visible spectra to give them an idea of
filters (not necessarily photographic filters), including Schott
notch filters, that might be used to enhance the contrast between
areas of abraded ink and non-inked parchment.  They have done all
the standard procedures of separating out the "green" vs the "blue
and green" channels in photoshop, inverting one image and enhance
with curves as necessary, etc.  They need to know if filtering of
some type will enhance the contrast.

Thus, I'm asking for either (1) the source of a UV-Visible spectra
of iron gall ink on parchment, or (2) the analysis of that spectra
calling out areas between about 300nm and 750nm that show
differences between parchment with iron gall ink and non-inked
parchment.

Tim Vitale
Print, Drawing, Photographs and
Electronic Media Conservator
Digital Imaging and Consulting
Preservation Associates
1500 Park Ave
Suite 132
Emeryville, CA 94608
510-594-8277


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                  Conservation DistList Instance 18:19
                 Distributed: Monday, October 25, 2004
                       Message Id: cdl-18-19-012
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