Compositional distinctions between 16th century 'façon-de-Venise ...

Table 2 Examples of individual Venetian and Antwerp glass compositions (in % m/m) compared with that of the Antwerp glass waste marble
‘Cristallo’ ‘Cristallo’ ‘Vitrum Blanchum’ ‘Vitrum Blanchum’ Goblet cluster 3 Glass marble
Constituent Venice3 Antwerp Venice3 Antwerp Antwerp Antwerp
Na O
2
MgO
15.5
2.35
15.1
1.29
12.5
3.05
13.6
3.79
14.9
2.15
15.7
1.90
Al O
2 3
SiO
2
P O
2 5
SO
3
Cl
0.48
72.7
0.13
0.30
0.75
1.38
71.3
0.21
0.19
0.69
1.40
68.6
0.37
0.28
0.88
1.19
66.9
0.36
0.29
0.67
1.43
65.67
0.35
0.18
0.79
1.58
65.4
0.44
0.13
0.90
K O
2
CaO
2.85
4.30
3.83
5.26
2.90
9.05
2.29
9.91
4.08
9.57
3.40
9.36
MnO 0.28 0.53 0.50 0.27 0.36 0.49
Fe O
2 3
BaO
0.19
n.d.
0.26
0.02
0.38
n.d.
0.32
0.02
0.43
0.05
0.50
0.02
PbO n.d. 0.01 n.d. 0.29 0.01 0.10
origin. The objects in cluster 3 can therefore in a direct way from Amsterdam belong to this group. For both clusters
be linked to local Antwerp production.
Na O+K O#20±2%. Cluster c and c have a similar com-
2 2 1 2
position to that of Antwerp clusters 3 and 4 (see Fig. 2), i.e.,
Comparison with literature data
with a composition similar to ‘Vitrum Blachum’ but with
Since in the Antwerp data one encounters both compositions
which are similar and those which are significantly different
from those found for the Venetian wares, it is relevant to
compare these data with the other published compositions of
Venetian/‘façon-de-Venise’ glass. In order to do so, the set of
122 Antwerp compositions was augmented with published
data series from regions geographically close to Antwerp.
Hierarchical cluster analysis was then performed on the large
data set. The first additional data set consisted of the 19
compositions published in Ref. 6 (Old Broad Street and City
of London); the second series consisted of seven soda-glasses
from Amsterdam5 and the third series are the French glass
compositions published by Barrera and Velde8 (about 100
pieces). In addition, the data published by Verità and
Toninato3,4 on truely Venetian glass were also included so as
to bring the total number of composition in the data matrix
to 254.
Fig. 5 shows the dendrogram obtained by clustering the
entire data set (again only the Na O, K O, CaO and MgO
2 2
concentration values were used). Table 3 lists the average
values of these oxide concentrations for each major cluster
shown in Fig. 5 (dotted lines). Clusters a and b include all the
‘Cristallo’ glass objects, the majority of the Venetian samples
belonging to cluster a with high Na O (17%) and low K O
2 2
(3%) content; cluster b contains less Na O, more K O and
2 2
about the same amounts of CaO and MgO. The Antwerp
glass objects with a ‘Cristallo’-like composition (see Fig. 2,
cluster 1) are divided over these two clusters, as are 30 French
vessels of similar composition. None of the London glasses
were found within these two clusters and only two objects
elevated K O (5–7% instead of 2–3%) The 19 Antwerp objects
2
of cluster 3, however, are now redistributed over clusters c
1
and e . Next to the Antwerp objects, one Venetian ‘Vitrum
2
Blanchum’ glass, most of the London glasses and 25 French
glasses belong to cluster c. Since this group also contains the
Antwerp glass marble, cluster c may be labelled ‘Antwerp
production’. The data in Table 3 again suggest that in London,
Amsterdam, various sites in northern France and Antwerp,
the same raw materials or bulk glass of the same origin were
used in the local glassworks or that glass vessels produced in
Antwerp were exported to these regions. Cluster d correspond
to the Antwerp cluster 2 in Fig. 1; also in France, a few objects
(five) with this high K O and relatively low Na O composition
2 2
are found. This mixed-ash group clearly corresponds to ‘non-
Venetian’ glass production. Whether this type of glass was
produced in Antwerp, however, cannot be established.
Clusters e and e show a fairly similar composition and
1 2
contain all the Venetian ‘Vitrum Blanchum’ glasses and the
Antwerp glass objects from clusters 3 and 5 (see Fig. 2).
Cluster e contains most of the Venetian ‘Vitrum Blanchum’
1
glasses, two London objects and 11 French glasses. Most of
the objects from Amsterdam belong to cluster e in addition
2
to some from London and a large group of French glasses.
When the dendrogram of the Antwerp glasses (Fig. 2) is
compared with that of the entire data set (Fig. 5), it appears
that largely the same data structure is found, i.e., in both
cases, in addition to both Venetian groups, a K O-rich ‘Vitrum
2
Blanchum’ variety and a small mixed-ash group is found.
It is also striking that both for ‘Cristallo’ and ‘Vitrum
Blachum’, two subgroups are formed (clusters a/b and e /e ),
1 2
where most of the Venetian wares are concentrated in one
(clusters a and e ) whereas the majority of the non-Venetian
1
finds tend to cluster together in the other subgroup (clusters
b and e ).
2
Conclusions
In view of the high price of finished Venetian products, it is
unlikely that all the Antwerp glass finds are Venetian products.
Either soda or sodium-rich ash (and possibly the other raw
materials for glassmaking), or soda-glass in bulk or finished
glass vessels must have been imported. In view of the presence
of the port, the cheapest and safest transportation route from,
e.g., Venice, Alicante or the Middle East to Antwerp, would
Fig. 5 Dendrogram obtained by hierarchical cluster analysis of the undoubtedly have been the sea. The aim of this investigation
total data set comprising analysis results from Antwerp, various sites was to determine whether there was a significant local pro-
in northern France, Amsterdam and London. duction of ‘façon-de-Venise’ glass vessels in Antwerp in the
J. Anal. At. Spectrom., 1999, 14, 493–498 497