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Introduction
Manganese stained glass
Accelerated light ageing
Conclusions Results
References
During the recent conservation work on
Sweden’s largest church window, The Son’s
window from 1892 in Uppsala Cathedral,
questions were raised about the type of
protective glass that should be installed.
Some of the stained glass was noticeably
discoloured and the concern was that the
process of discolouration would continue if
not appropriately protected from sunlight.
The chemistry of a “browning” phenomenon
of manganese compounds in glass (present
as either colourant, decolourant, impurity or
contaminant) has been studied extensively by
other researchers [1-4].
The presence of manganese in the
discoloured glass was confirmed by non-
destructive X-ray fluorescence spectroscopy
(XRF).
At the Swedish National Heritage Board a
small area (2 cm2) with both original “light”
and discoloured “dark” stained glass was
exposed to accelerated light ageing under a
high UV metal halide lamp. The exterior side
of the glass piece was directed towards the
light source.
Spectral reflectance curves of the light area measured from the
interior side of the glass piece. Upon light ageing the curves
decrease in reflectance to approximately the same level as the
naturally dark area and a bit further.
The accelerated ageing investigation on a
manganese containing stained glass from the
late 19th century showed that the greatest
extent of colour change had already occurred
and that any additional colour change would
most probably not be noticeable by eye.
Following this project, it was decided to install
one of the more aesthetic protective glasses,
slumped float glass with a thin wash, rather
than the more expensive option of a full UV
protective glass.
1. J. Ferrand, 2014. Le phenomene de brunissement des vitraux
medievaux: criteres d'identication et nature de la phase d'alteration,
PhD Thesis, Universite Paris-Est. (French) https://tel.archives-
ouvertes.fr/tel-00962174 (accessed 2016/05/04)
2. J. Ferrand, S. Rossano, C. Loisel, N. Trcera, E. D. van
Hullebusch, F. Bousta and I. Pallot-Frossard, 2015. Browning
Phenomenon of Medieval Stained Glass Windows, Analytical
Chemistry, 87(7), pp 3662–3669.
3. S. Cagno, G. Nuyts, S. Bugani, K. De Vis, O. Schalm, J. Caen, L.
Helfen, M. Cotte, P. Reischig and K. Janssens, 2011. Evaluation of
manganese-bodies removal in historical stained glass windows via
SR-μ-XANES/XRF and SR-μ-CT , Journal of Analytical Atomic
Spectrometry, 26, pp 2442-2451.
4. G. Nuyts, S. Cagno, S. Buganic and K. Janssens, 2015. Micro-
XANES study on Mn browning: use of quantitative valence state
maps, Journal of Analytical Atomic Spectrometry, 30, 642-650.
LIGHT AGEING OF DISCOLOURED MANGANESE STAINED GLASS
FROM UPPSALA CATHEDRAL
Erika Andersson1, Marei Hacke2, Kaj Thuresson2, Yvonne Fors2
1 Uppsala Cathedral Stained Glass Studio, Svenska Kyrkan i Uppsala, Box 897, SE-751 08 Uppsala, Sweden, erika.s.andersson@svenskakyrkan.se
2 Riksantikvarieämbetet / Swedish National Heritage Board, Kulturvårdsavdelningen, Konserveringsvetenskap / Conservation Science, Box 1114, SE-621 22 Visby, Sweden
0 5 10 15 20
- keV -
0.0
1.0
2.0
3.0
4.0 x 1E3 Pulses
Si
Si Ca Ca
Mn
Mn
Fe
Fe Cu
Cu Zn
Zn
Sr
Sr
Sr
Ba
Ba
Ba
Pb
Pb
Pb K
K
Uppsala Cathedral (photo by Mark Wilson: Wikimedia commons)
Conservators at Uppsala Cathedral Stained Glass Studio working on
a panel of The Son’s window (photo: Johan Nilsson)
Along the upper part of the image is an area that had been shielded
from sunlight by a synthetic mastic and the lug bar (which secured
the panel in the window), now showing that the colour has changed
from pinkish brown to a darker brown. The XRF spectrum was
obtained from a discoloured area of the pink-brown stained glass
piece (top right in image)
The discolouration process was followed
spectrophotometrically through regular
reflectance measurements of the “light” and
“dark” areas from both the interior and the
exterior sides of the glass piece.
Pink-brown stained glass piece showing the area that was exposed
to accelerated light ageing (grey) and the “light” and “dark” areas
used for colour measurements.
light area
dark area
After eleven days of accelerated light ageing
the lighter area had discoloured to nearly the
same level as the naturally aged dark area.
Accelerated ageing was carried on for
another eight days with the UV filter removed,
causing both the light and dark areas to
discolour further. However, despite the
addition of UVB and UVC light, the
discolouration continued at a slower rate. The
further “browning” was measurable by
spectrophotometry but it was not visible by
eye.
Spectrophotometric measurements expressed in units of colour
change (delta E 2000) and plotted againts the total irradiance of UV
light received by the glass piece during nineteen days of accelerated
ageing.
The logarithmic trendlines in the graph above
show that the rate of change starts to level
off.
The colour change for the previously
unexposed light area was significant and
reached ~7-8 ∆E values after eleven to
fourteen days of ageing which represented
the natural colour change “browning” that had
occurred over the entire glass piece where it
had been exposed to sunlight.
The additional ~1-2 ∆E values caused by
further light ageing up to nineteen days were
not noticeable by eye. Similarly, the colour
change of ~1-2 ∆E values induced in the
already sunlight exposed dark area was
measurable but not noticeable by eye.
Accelerated ageing was carried out for a total
of nineteen days, of which eleven were with a
UV filter installed and eight without. The
filter cut nearly all radiation < 295 nm) and
reduced the UVA part of the lamp spectrum.
Sol lamp spectrum (with H2 filter, grey; without filter, purple) and
sunlight spectrum as measured on a sunny day in May in Visby,
Sweden
µW/cm2/nm
2
