Paper Conservation: Decisions & Compromises

locally to prevent its continued deterioration;
and 7) rebind the Atlas in a historically sympathetic
binding.
Method
XRF was conducted using a Bruker Tracer TurboSD
spectrometer with a rhodium anode and
silicon drift detector. The instrument was operated
with vacuum pumping, a titanium filter,
and either 15 kV and 55 μA or 40 kV and 20 μA
for 180 seconds. Results were analyzed quantitatively
with Bruker Calprocess software and linear
calibration from metal-doped samples of Whatman
paper developed at LC; due to imperfect
calibration standards, quantitative results have
up to about 20% uncertainty depending on the
element and variation in the paper (4). Initial UV
fluorescence examination was done with a hand
held UVL-56 Blak-Ray lamp at 366nm. More extensive
spectral imaging was conducted on select
maps before and during treatment using a Mega
Vision Monochrome E6 39 Megapixel camera system
and light emitting diodes (LED) illumination
at 13 narrow spectral bands from the UV through
the infrared range.
Results and Discussion
Following disbinding and guard removal, conservators
tested alum removal in guards taken from
the deteriorated maps by blotter washing on a
suction table with either a 50% ethanol-modified
aqueous solution or a pH 7.5 aqueous solution.
XRF measurements before and after treatment
showed that the ethanol-modified blotter
washing only removed about 40% of the alum,
while pH 7.5 water easily removed the agent, as
measured by K concentration. After testing the
guards, the Nona Asiae Tabula (Fig. 2) was chosen
for initial map treatment because it had significant,
white alum surface deposits, was the least
fragile of the maps in poor condition, and was
the easiest to handle.
The conservation treatment involved four
separate steps of blotter and suction table washing
using various solutions. The first treatment
used 50% ethanol and 50% water adjusted to pH
8.0 with Ca(OH) 2
. XRF measurements indicated
that only about 25-30% of the alum agent was removed
by this method; however color sensitivity
to water led us to try this protocol first. Nevertheless,
this solution caused minor color transfer.
The second step focused on local treatment of
offset staining from verdigris. Here ethylenediamine
tetraacetic acid (EDTA) and NaBH 4
were
successful at removing excess copper from the
paper and reducing the staining. However, EDTA
left a residue in the paper that is visible with
UV fluorescence. In the third step, blotters used
for washing were wet with aqueous solution
brought to pH 8.5 using calcium hydroxide. This
was effective for removing the excess alum in the
paper overall. By not spraying the recto, we were
able to minimize movement of color. The fourth
treatment used calcium bicarbonate-saturated
blotters in an attempt to increase the amount of
calcium left in the paper. Table I describes the
succession of steps, the solutions used, and the
results obtained; Table II shows XRF results for
paper areas, excluding the offset stains.
After treatment, the Nona Asia Tabula map appears
significantly brighter, treated staining
from verdigris offset is considerably reduced,
and the paper feels stronger and more flexible.
XRF analysis of the map and blotters before,
during and after treatment shows the effective
removal of potash alum in the paper as well as
copper in areas of verdigris offset. Copper content
in areas treated near verdigris does not appear
increased, within the margin of error. EDTA
residues remain in treated areas, as detected by
UV fluorescence, and are the subject of further
study.
Conclusion
The value of combined XRF and spectral analysis
as treatment monitoring and decision-making
tools is demonstrated as an integral part of the
conservation of a 16 th century atlas with verdigris
and old restoration damage. The treatment
of one map has been a step-by -step process of
trial and review, involving analytical monitoring
and compromises. This process has lead to
formulation of detailed procedures for six other
maps in the volume in poor condition, as will be
discussed. Current conservation measures include
removal of a potash alum-based “strengthening”
agent by blotter-washing with pH-adjusted
aqueous solutions on a suction table. Development
of methodology for reduction of copper
staining and possibly also conversion of browned
verdigris is in process with the aid of these tools
and Raman spectroscopy.
ICOM-CC Graphic Documents Working Group Interim Meeting | Vienna 17 – 19 April 2013
31