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The Museum of Ancient Glass in Zadar (Croatia)
Šime Perović
Museum of Ancient Glass in Zadar
Zadar, Croatia
[email protected]
Abstract
This paper discusses the establishment of a glass museum
in Zadar following the discovery of Roman glass finds,
and describes its role in the study and conservation of this
collection. It outlines the restoration of objects prepared
for display in the museum, and provides the results of experiments in reproducing several types of Roman blown
and fused glass.
Keywords: Zadar, archaeology, Roman glass, restoration,
glass museum
Introduction
A significant quantity of ancient Roman glass has been
uncovered in and around Zadar, Croatia, indicating that
glass was pro­duced in this area (Fadić 1997, pp. 73–246).
The preparation for exhibition of glass finds from the Roman province of Dalmatia prompted a wide range of professional and scientific activities.
The Museum of Ancient Glass in Zadar (Fig. 1), which
has a large collection of ancient Roman glass (Fig. 2),
opened in the spring of 2009. The museum focuses on the
manufacturing techniques and aesthetic value of glasses
made in the Roman world (Domijan 2009). Most of the
objects on display came from excavations at Roman ceme­
teries in Zadar (Iader), Nin (Aenona), Starigrad (Argyrun­
tum), and Podgrađe (Asseria). These excavations recovered more than 3,000 complete objects and a comparable
number of pieces requiring restoration.
Many glass objects were found in rescue excavations in
the Relja district of Zadar (Fadić 2006b). About 2,000
graves containing considerable quantities of glass objects
Figure 1
Museum of Ancient Glass in Zadar.
Figure 2
Part of the museum’s Roman glass collection.
75
Figure 3
Glass urn (olla) on the archaeological site (left) and after restoration (right).
were uncovered here. These finds prompted the establishment of the museum for the display and study of these
artifacts, including conservation and restoration work.
While the excavations in Starigrad and Podgrađe were
conducted in the early 1900s, those at the Roman cemetery in Zadar are more recent (Gluščević 2002). At each
cemetery, evidence of both inhumation and cremation
was found. Both of these burial rituals were practiced
dur­ing the Roman imperial age, although the former prevailed in the later part of that period. Some inhumations
in Dalmatia were accompanied by the construction of
graves, while others were not, and cremated remains were
found in urns made of ceramics, stone, or glass (Fadić
2006a, pp. 7–91). Above the sepulchers stood several
types of tombstones (stella, cippus, ara, and epitaph). The
long-term use of the Zadar cemetery is confirmed by the
discovery of Liburnian sepulchers dating from the seventh century B.C. and inhumation tombs from the late
fifth and sixth centuries A.D. Most of these graves are
dated between the first and fourth centuries A.D.
The typology of glass artifacts from the cemetery of
Zadar is extremely broad. Among the finds are mosaic
cups, game counters, bottles, jugs, plates, dishes, beakers,
urns, toilet bottles, droppers, amphorae, and decorative
pins and other jewelry (Isings 1957). All of them came
from tombs (Fadić 1997, pp. 73–246), which also yielded
oil lamps, coins, ceramic artifacts, metal objects, and pins
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Perović
made of animal bone. These items were usually offered to
assist the deceased in the afterlife, and they reflected his
or her social status, occupation, and age.
The size of the collection of Roman glass from the wellpreserved cemetery at Zadar is comparable to that of Aqui­
leia in northern Italy (Mandruzzato and Marcante 2007,
pp. 4–94). These burial items were widely used in everyday
life. For example, large glass urns (olla), which contained
the cremated remains of the dead, were also employed in
storing vegetables (Fadić 2006a, pp. 7–91; Fig. 3). Toilet
bottles, which contained perfumes and balsams, were also
used in cremation, and prismatic jugs served as measuring
vessels for liquids and as tableware (Nappo 2004).
The Museum of Ancient Glass encompasses a wide
range of museological, educational, scientific, and research
activities. It includes a facility for the research of ancient
glass technologies, a department of restoration, a library,
and offices for editorial work on the archaeological periodical Asseria. There is also a workshop in which glassmakers produce about 20 types of Roman glasses; visitors
are also invited to make glasses, some of which are filled
with olive oil and lavender oil.
Glass Restoration
The conservation workshop of the Archaeological Museum Zadar has restored items of wood, metal, ceramic,
stone, and paper, as well as glass artifacts dating from the
Roman and medieval periods (Batović 1980). This work
is now also performed in the Museum of Ancient Glass,
where the most demanding interventions are made (Pe­ro­
vić 2008). Special attention is focused on nondestructive
chemical and physical analyses, and high-magnification
examinations are supplemented with spectroscopic measurements and particle-induced X-ray emission (PIXE)
analyses that are made in collaboration with the Ruđer
Bošković Institute in Zagreb (Perović forthcoming). These
studies provide information on glass compositions, including coloring and opacifying agents (Arletti and others
2006). Our experiments are designed to determine the
composition of opaque Roman glasses. We found, for
example, that objects made by reheating crumbled glass
(pasta vitrea) (Moretti 2002, pp. 61–68) were similar to
other opaque glasses (Perović forthcoming).
One hundred glass objects were restored for permanent exhibition, and 21 objects required intensive intervention.
Although the composition of Roman glass is homogeneous, differences in degradation are normally based on
variations in the composition of local soils. Degradation
leads to weathering, after the leaching of alkalis from the
network of the glass (Pallecchi 2000) caused by the effects
of humidity on the glass. The absorption of water is the
primary means of forcing alkalis to migrate toward the
glass surface, where they leave behind layers that laminate
and scale. In addition to weathering, some glasses show
Figure 4
Process of devitrification, shown at magnification of 40X.
evidence of poor annealing (ibid.). Such objects have a
tendency to form microcracks (about 0.1 mm; Fig. 4).
They need to be restored to stable microclimatic conditions (relative humidity [RH] of 55%, and temperature of
18°–20°C), so as to slow the degradation processes (Hill
1993). RH values suggested by other authors for the storage of archaeological glass range from 40% (Daintith
1988, pp. 5–18) to 45%–50% (Venturini 2000). We have
chosen the value of 55% RH because we are treating mainly fresh archaeological finds that are in good shape, and
we want to avoid any stress or shock that might result from
changing their microclimatic environment.
Stage 1: Stabilization and Cleaning
Modern methods of preserving and restoring ancient
glass artifacts can be divided into two stages. The first involves the stabilization and cleaning of the object (Daintith 1988, pp. 5–18; Venturini 2000). The most important
function of stabilization is to slow the processes of weathering and devitrification. Many of the samples in the Department of Restoration and Research in the Museum of
Ancient Glass in Zadar required treatment of this kind.
The cleaning was normally done with mechanical tools,
motor-driven brushes, and scalpels, while the most delicate interventions were carried out under the microscope.
The most resistant impurities were treated in a solution of
alcohol and demineralized water.
Stage 2: Restoring the Glass
The first step in restoring the glass is recomposition by
gluing the fragments with a slow-bonding adhesive. This
so-called indirect gluing process avoids the mistakes in
the angle of the fracture connections that are inevitable
in direct gluing. It is impossible to connect all of the fragments at an ideal fracture angle, and thus an object cannot
be reassembled properly with direct gluing. We join fragments by the application of a special prosthesis or clamp
made of brass or copper. Cyanoacrylate glue is normally
used to affix the prosthesis to the surface of the glass, and
after all of the fracture angles have been adjusted, we inject the glue into the cracks. The catalysis of the glue requires 24 hours, after which the prosthesis is removed
with special solvents (Petek 2004). In the case of objects
with very thin walls, which could not survive the use of a
metal prosthesis, we employ tape in rejoining fragments.
The Museum of Ancient Glass in Zadar (Croatia)
77
Figure 5
Type of integration for structural stability.
The next step in restoration is integration, which is carried out for structural stability (Fig. 5) or aesthetics (Fig.
6). In the latter instance, missing parts of objects are replaced with synthetic reconstructions. On a large glass
cup (modiolus) of which about 35 percent of the body was
missing (Fig. 6a), for example, a replacement was made
by injecting epoxy into a two-part silicone mold. The
mak­ing of such molds is sometimes a complicated pro­
cedure (Mertik and Lemajič 2007), which involves the
preparation of a matrix—a complete positive of the artifact—before the mold is created. Modeling wax or clay is
normally used in the production of the matrix. After the
positive is designed, the mold is prepared with silicone
rubber of sufficient hardness. The mold must then be retouched by a fast-rotating polisher and attached to the
damaged artifact. Figure 6b shows the preparation for injecting the synthetic material inside the prepared mold.
This type of integration is particularly necessary when
objects such as the Zadar modiolus are to be placed on display (Perović 2008; Fig. 6c).
Figure 6a (above, left)
Type of integration for aesthetics.
Figure 6b (above)
Processes of recomposition and restoration
with two-part silicone molds.
Figure 6c (left)
The object (modiolus) after intervention.
78
Perović
Figure 7
Museum facility for glass
experiments.
Figure 8
Production of copies of
Roman blown glass.
Three considerations govern our restoration work: (1)
reversibility, (2) minimal intervention, and (3) accentuating reconstructed parts, which must be different in appearance from the original. In our effort to respect the
original construction of an object, we sometimes attempt
to make a reconstruction that is stable and then create
copies made of glass or synthetic materials in the museum’s workshop (Fig. 7).
Experiments in the workshop are designed to help us
understand how ancient artisans fashioned glass objects,
especially by glassblowing (Stern 1995, pp. 34–44). The
nearly 20 forms of beakers and other objects (Fig. 8) are
made with two- or three-part wooden or metal molds. We
work with various recipes, and we are researching the
techniques of manufacturing “archaeological” glass described by Moretti (2001). An example of our experimental work is the reproduction of a polychrome glass
bowl dating from the first century A.D. (Fig. 9). We applied a cylindrical mold and the fusion technique in order
to make a copy of this artifact (Fig. 10). In general, the
materials used for fusing glass in molds have different
thermal characteristics that create stresses when an object
is annealed. To eliminate problems, we tried to choose
materials and shapes that can withstand these stresses.
Sipo­rex, an aerated concrete that is employed by civil engineers, showed optimal characteristics for this purpose.
It is very inexpensive, and that is an important considera­
tion because the mold, which can be easily shaped, should
Figure 9
Dish made of fused polychrome canes: copy (a) and original (b).
The Museum of Ancient Glass in Zadar (Croatia)
79
References
Arletti and others 2006
Rosella Arletti and others, “Roman Coloured and
Opaque Glass: A Chemical and Spectroscopic Study,” Applied Physics A: Materials Science & Processing, v. 83, no. 2,
2006, pp. 239–245.
Batović 1980
Šime Batović, “Rad Arheološkog muzeja u Zadru od
1973. do 1976. godine,” Diadora (Zadar), v. 9, 1980, pp.
549–617.
Figure 10
Mold for fusing glass.
be used only once. For the reproduction of the bowl, we
employed a four-part mold (Fig. 10). We placed the decorated glass disk inside the mold and heated it in the kiln.
The spaces between the parts of the mold served as absorption areas, which, together with the absorption capability of the aerated concrete, allowed us to successfully
reproduce the ancient glass piece. After fusing, the bowl
had to be cut to smooth and polish the rim.
Conclusion
The recently opened Museum of Ancient Glass houses a
large collection of Roman glass that was uncovered in sev­
eral archaeological excavations at ancient cemeteries in
and around Zadar. It includes a facility for conducting
experiments that are designed to explore ancient glassmaking techniques, as well as a department for restoring
broken or damaged objects. About 100 objects have been
restored, and 21 have undergone intensive work.
In addition to developing all of the museum’s departments, future goals include extending collaborative efforts
with other cultural, educational (e.g., Zadar University),
and tourist organizations in Zadar. The museum should
also become a key Croatian institution for research on
glass and glassmaking.
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The Museum of Ancient Glass in Zadar (Croatia)
81
Glass and Ceramics Conservation 2010
Interim Meeting of the ICOM-CC Working Group
October 3–6, 2010
Corning, New York, U.S.A.
Hannelore Roemich, Editorial Coordinator
ICOM Committee for Conservation
in association with The Corning Museum of Glass
© 2010 International Council of Museums
ICOM-CC Glass and Ceramics Working Group Committee:
Gerhard Eggert
Coordinator
Hannelore Roemich
Editorial Coordinator
Review Panel for Papers
Renske Dooijes, Leiden, The Netherlands
Gerhard Eggert, Stuttgart, Germany
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Stephen P. Koob, Corning, New York, U.S.A.
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For The Corning Museum of Glass:
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Design and Typography: Jacolyn S. Saunders
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ISBN: 978-0-87290-182-7
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Cover Image:
Cire perdue figure made by Frederick Carder
in the 1930s or 1940s, with a repair in which
the epoxy is badly yellowed. The Corning
Museum of Glass (59.4.426).