Paper Conservation: Decisions & Compromises

Fig. 2
Atlas, the Crown papers are in very good condition,
exhibiting quite white color and expert
sheet formation. These watermarks appear identical
to those that make up the separate sheets of
LC’s prized sixteenth century Map of the World
printed by Martin Waldseemüller. The Lily papers
are in fair to good condition, but the pulp
is less evenly processed and dispersed, and the
sheet is generally not as white in color. On the
other hand, a large portion of the papers without
watermarks are in markedly poor condition
and show deterioration of the green pigment.
Compared to the Crown or Lily papers, this pulp
is clearly less well-processed, the formation of
the sheet is rather uneven, and the paper is light
brown to tan.
Non-invasive, quantitative X-ray fluorescence
spectroscopy (XRF) analysis of the papers used
in the Rosenwald volume and other LC copies
of Ptolemy’s Geographia strongly suggests a
correlation between condition and elemental
composition in the paper. The Crown papers have
a calcium (Ca) to iron (Fe) ratio of about 16:1. In
contrast, Lily and unwatermarked papers in poor
condition contain Ca:Fe ratios of about 6:1. This
evidence suggests that the presence of a relatively
large quantity of Ca and low proportion of
Fe, combined with high quality processing, has
helped protect maps and colorants from degradation,
even in the presence of the copper-based
green pigment, which was confirmed by polarizing
light microscopy to be verdigris (2). The
other colorants appear to be organic-based and
remain unidentified. The difference in inherent
paper quality is further supported by our observation
that in four different copies of the Atlas,
the same maps appear brown, even in uncolored
versions.
Records show that in 1938, Philadelphia dealer
A.S.W. Rosenbach sold the book to Rosenwald,
who subsequently donated it to LC. Cover board
pastedowns and repairs on the maps provide us
with good evidence that the Atlas had undergone
several rebindings including one in the mid-20th
century. These conclusions are pertinent to the
analytical finding of a heavy brush application of
potash alum/gelatin solution on the seven maps
in poor condition. This agent was most likely applied
during the last rebinding in an attempt to
strengthen papers that had become weakened
during natural aging. What is remarkable is that
this “strengthening” treatment coincides with
poor condition of both verdigris and the paper
support. This lies in sharp contrast to maps still
in good condition, which show the presence
of relatively minor amounts of potassium (K)
and sulfur, from original preparation for handcoloring,
that remains benign in its influence
on aging. In addition, close examination of the
restored maps shows that while the verdigris has
turned brown in most of these maps, it remains
bright in the gutter regions, where a guard paper
with a high Ca:Fe ratio plus significant amounts
of zinc (Zn), was adhered. These guards were in
place before the alum agent was brushed onto
select maps, protecting the paper and verdigris
pigment in the centerfold from further discoloration
both physically and through the beneficial
action of Ca- and Zn-containing compounds.
With many of the questions regarding the Atlas’
condition and history answered, the current
project goals address the conservation treatment
approach and methodology. This paper describes
the use of quantitative XRF, along with spectral
examination, as decision-making tools during
treatment. Based on the initial technical examination
and analysis, the following treatment
plan was established: 1) remove the non-original
binding; 2) remove guards from deteriorated
maps that need stabilization or that prevent
complete opening of folios; 3) remove the potash
alum-gelatin strengthening agent from the seven
restored maps; 4) reduce discoloration from verdigris
offset; 5) restore a better Ca:Fe balance in
the conserved maps; 6) treat the altered verdigris
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013
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