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By Jeffrey Levin
Its most impressive hour may be night.
When darkness removes most traces of modernity and lights from
below shine upon it, Prague Castle looms over the red-tile-roofed
buildings that surround it with a sweeping grandeur that knows few
equals. The 20th century slips into the shadows, leaving behind
the architecture of history.
For a thousand years, the castle on Hradcany Hill has been the
political and religious heart of Prague and the lands of Bohemia.
The seat of government for kings, emperors, and presidents, it grew
over the centuries, becoming the largest medieval castle in existence.
Just as Prague Castle visually dominates the city whose name it bears, St. Vitus Cathedral dominates the castle. Located in the center of the castle grounds, St. Vitus is massive and imposing, its Gothic spires towering above the 18th century buildings that mark the castle's perimeter. Begun in 1344, it is the third church to stand on the site. Here, in this place, Bohemian kings were crowned.
Here, too, they are buried. Among those reposing within the cathedral
is the nation's patron saint, St. Wenceslas, a prince of Bohemia
murdered in 929 by his pagan brother.
When daylight returns to Prague, St. Vitus remains the city's most
striking architectural landmark. Yet even the sun does not fully
reveal on its exterior one of the cathedral's great artistic treasures—a rare medieval glass mosaic. Out in the open, but nevertheless
barely seen, it is obscured as the result of a combination of weather,
climate, and the elements of its own composition.
The Last Judgment
Six hundred years after the death of Charles IV—King of Bohemia
and Holy Roman Emperor—Prague bears witness to the imperial ruler's
vision of his chosen capital. A man of education, diplomatic skill,
and religious feeling, Charles transformed the city into a political,
cultural, and economic center, establishing the first university
in central Europe, planning a new district for the city (Nové
mesto, or New Town), and initiating numerous public works that
still stand: the Carolinum, the university's central hall; the tower
of the town hall in Old Town square; and the Charles Bridge over
the Vltava River, which divides the city. Of all of Charles' projects,
the most ambitious was undoubtedly St. Vitus Cathedral.
In 1370, the Emperor ordered the creation of an unusual work of
art on the exterior of the cathedral's south entrance. The entrance,
which faced the emperor's residence and served as the entry point
for coronation processions, was to have over its three portals a
glass mosaic depicting the Last Judgment.
Mosaic making was not a craft common to the Bohemian artisans of
the time. Still, according to records, this large and complex glass
mosaic was completed by the following year. In the center of the
mosaic, Christ is encircled by a mandorla (an almond-shaped aura
of divinity) surrounded by angels. Kneeling beneath this image are
the saints of Bohemia and, below them, Emperor Charles IV and his
fourth wife, Elizabeth of Pomerania. The panel to the left depicts
heaven, while the right panel depicts hell.
The speed and quality with which the mosaic was executed fuels
one of the lingering mysteries of its creation. Who performed the
work on The Last Judgment? In technique and style, the mosaic
resembles one found at Orvieto Cathedral in the Umbrian region of
Italy, the single other Gothic building in Europe with a large exterior
glass mosaic. Some experts believe that only Italian craftsmen (perhaps
even those who worked on Orvieto) would have had the experience
and skill necessary to accomplish in such a relatively short period
the remarkable work in Prague. The fact that Charles IV himself
had journeyed to Italy just a few years prior to the mosaic's construction
adds weight to this contention.
But a close examination of the faces of the figures in the mosaic
prompts a glimmer of doubt. The features are clearly Slavic in appearance,
a physiognomy quite different from that found in the works of Italian
mosaicists. How likely is it that Italians would have created facial
characteristics such as these?
There are, unfortunately, no documents from the period that might
have solved this puzzle. Such items as bills for the construction
of the cathedral were archived beginning in 1372—one year after
the mosaic's completion.
While questions may always remain regarding the artisans who made
the mosaic, its extraordinary quality is not in doubt. "This is
a unique object of visual art which has no companion east of the
Rhine and north of the Alps," says Dr. Eliska Fucíková,
Director of the National Heritage Department of the Czech Republic's
Office of the President. But for much of its existence, this rare
work of art has gone unseen. Sitting in her office in Prague Castle,
the ringing of noonday bells heard through her open window, Dr.
Fucíková explains the mosaic's "sad story." Although
it has been cleaned and covered with protective coatings on a number
of occasions in its history, over time the mosaic eventually always
vanishes beneath a whitish, opaque layer of corrosion products that
cover its surface. Such is the case today.
"It's absolutely invisible," she says. "If you tell someone there
is a mosaic there, the obvious question is 'Where?'"
Standing in the castle court near the cathedral's south entrance,
one can see that the mosaic is indeed obscured, as if dusted with
a coat of chalk. Of the 31 shades of colored glass that make up
The Last Judgment, all that emerge are a dull, rusty looking
red, a pale green dimly reminiscent of tarnished copper, and gold,
primarily in the upper left and upper right corners, from an early
20th century restoration. Figures can be seen, but most details
and facial features cannot.
All in all, the mosaic appears bleached and faded, vanishing beyond
discernment.
The Mosaic's Conservation
Since October 1992, the Getty Conservation Institute (GCI) and
the Office of the President of the Czech Republic have been collaborating
on a project to conserve the St. Vitus mosaic. This effort comes
after a series of interventions on the mosaic, the first as early
as the 15th century, followed by at least one or two in the next
century. In 1619 the mosaic was reportedly plastered over, but it
was later uncovered and restored. A series of restorations was conducted
in the 19th century, the most drastic occurring in 1890, when the
mosaic was removed from the cathedral wall in 274 sections and placed
in storage until 1910, when it was reinstalled and repaired.
Beginning in the 1950s, the mosaic again underwent a number of
treatments to deal with the continuing problem of clouding over.
Each treatment proved successful only temporarily. Part of the problem
was the Communist government's failure to heed the advice of the
Czech conservators conducting the treatments who urged that a consistent
regimen of cleaning be maintained.
By the mid-1980s, The Last Judgment had vanished again.
When the GCI approached the government in Prague about developing
a joint conservation project, the St. Vitus mosaic was at the top
of the Office of the President's list of conservation priorities. The objective of the project is the mosaic's thorough cleaning,
followed by the application of a treatment that will dramatically
slow the return of the opaque layer. However, as is standard with
GCI special projects, intervention is being preceded by a complete
review of existing documentation, a thorough study of the causes
of the problem, and an extensive investigation of possible treatments.
A good deal of information on the mosaic's past restorations has
been culled from the Prague Castle archives. The project team also
consulted with Czech conservators who worked on the mosaic in recent
decades, and reviewed their records. In addition, two Italian mosaic
specialists who had worked on St. Vitale Church in Ravenna were
brought in to examine The Last Judgment and report on its
current condition. They concluded that while it will be a great
challenge to avoid "a repetition, after restoration, of the corrosion
process now in progress," the mosaic generally remains in good condition
beneath the present corrosion layer.
It is already clear that the kind of glass used in the mosaic,
which differs from Italian glass, is a factor in the corrosion process.
The making of glass involves the melting of sand (i.e., silicon
dioxide) with a flux such as soda (sodium carbonate). In central
Europe, unlike Italy, soda was not easily available in medieval
times, so glassmakers used potash (potassium carbonate), which was
extracted from the ashes of burned wood.
"While soda and potash are similar compounds, glass made of potassium
is less stable and more soluble than sodium-based glass," explains
Dr. Dusan Stulik, Acting Director of the GCI's Scientific Program
and project leader for the St. Vitus effort. "The potassium-based
composition of the St. Vitus mosaic's glass is a real problem."
Another factor is the protective coatings of waxes and resins of
various kinds that have been applied since the reinstallation of
the mosaic. These coatings themselves have degraded and contributed
to the mosaic's near opacity today.
The mosaic's problems are exacerbated by its location. While most
Italian mosaics are situated in interiors or in some way sheltered,
The Last Judgment is completely exposed in a climate with
greater extremes than those found to the south. In addition to being
subjected to wind, rain, and snow, the mosaic, on the south side
of the cathedral, can heat to up to 52 degrees centigrade during
the summer and drop to minus 20 degrees in the winter. An environmental
monitoring station, installed in June 1993 by Shin Maekawa of the
Getty Conservation Institute, recorded this information, as well
as data on air temperature, relative humidity, dew-point temperature,
wind speed and direction, and solar radiation. All the data are
being integrated in the development of long-term conservation strategies
for the mosaic.
Treating the Problem
Early in the project, the GCI team met with a group of leading
Czech conservators to help develop a consensus on intervention.
Prior to the Institute's involvement, there were two schools of
thought within the Czech conservation community: one group believed
that the mosaic should be removed, new housing found, and the original
replaced by a copy; another group maintained that the mosaic should
be treated in situ. After a series of discussions, the Czech group
came to the consensus that treatment in situ was the appropriate
approach.
Encompassing 84 square meters (904 square feet), the mosaic contains
about one million tesserae, most approximately one centimeter in
size. In April 1994, photographic documentation of the entire mosaic
was performed. Three hundred images were made, detailing the mosaic's
present condition. Transferred to photo compact discs, the images
will enable conservators to create high-resolution condition maps
of the mosaic.
Investigation has already begun into possible treatments to be
applied to The Last Judgment once cleaning is complete. The
GCI is working with the Fraunhöfer Institute for Silicate Research
in Würzburg, Germany, testing several treatments including
a composite treatment that has been used on medieval stained glass.
Part of the treatment testing program are ten small test mosaics
and one large one. Each test mosaic contains several different tesserae
including: (1) test glass, developed by the Fraunhöfer Institute,
with a known corrosion rate; (2) original tesserae from the mosaic
(discovered in archives and presumably left from the mosaic's removal
in 1890); and (3) three types of modern mosaic glass. The test mosaics
have all been treated with different materials being considered
for use at St. Vitus. In May 1994, the large test mosaic was installed
in the vicinity of the cathedral. The smaller test mosaics are being
subjected to accelerated aging experiments at the GCI and in Würzburg;
these experiments simulate cycling of temperature, humidity, UV
radiation, and pollutant concentrations. The results will determine
whether coatings can protect the mosaic from the extremes of climate
to which it is exposed and, if so, what the maintenance cycles of
cleaning or recoating will have to be.
While actual treatment of The Last Judgment is anticipated
in early 1996, all involved, including the Office of the President,
are emphasizing thoroughness over speed.
"They want us to make sure that everything is done properly, so
there isn't any pressure applied on us time-wise," says Dr. Stulik.
"This kind of patience is unusual, but very appropriate given the
mosaic's past problems."
Born and raised in Prague, Dr. Stulik well understands the desire
of the Czech government to be certain that the St. Vitus mosaic
is returned to visibility with great care. If the cathedral is the
heart of Prague Castle, then the mosaic is arguably at its most
precious spot. In a chamber of the cathedral behind the mosaic is
the royal treasury where the Bohemian coronation jewels are stored.
Beneath the chamber is the Chapel of St. Wenceslas. From the standpoint
of history, observes Dr. Stulik, "this was the center of power and
religion."
An Emperor's Legacy
When Charles IV died in 1378, St. Vitus Cathedral had been under
construction for 34 years. But despite three and a half decades
of work, the cathedral was centuries from completion. War, internal
strife, and other problems interrupted the building's progress,
and it was not until 1929, exactly a thousand years after the death
of St. Wenceslas, that the cathedral was finished. By then, The Last Judgment mosaic had passed from sight numerous times, only
to be resurrected by new generations seeking to recover Prague's
medieval masterpiece.
Today in the Prague Castle courtyard in front of the cathedral's
south entrance, tourists wander through, mostly oblivious to the
unique creation close at hand. Occasionally a guide will point out
the mosaic to the visitors gathered around him or her, and they
will look up, squinting, trying to make out the stunning art that
lies beneath the white layer of corrosion.
Perhaps some day soon they will need no one to show them The Last Judgment. Instead, as they turn the corner into the courtyard,
the glass mosaic, its colors brilliant in the sun, will capture
their vision without coaxing, and they will gaze with awe and amazement
at an emperor's shimmering legacy.
Jeffrey Levin is Editor of Conservation, The GCI Newsletter.
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