Cultural Heritage Applications: Archaeological Ceramics and Building Restoration - On Statistical Pattern Recognition in Independent Component Analysis Mixture Modelling - page 138

Table 6.5 Statistics of the stratified random sampling for open porosity and apparent density

N i

r

N i n i
N i

r n i

n i l i

l i 2

Open porosity 1. Bronze Age 47 5 29,30 27,70 30,90

2. Iberian 155 16 22,50 21,71 23,29

3. Roman 138 35 32,00 30,78 33,22

4. Middle Ages 140 23 23,80 22,78 24,82

Apparent density 1. Bronze Age 47 5 1,85 1,82 1,88

2. Iberian 155 17 1,77 1,75 1,79

3. Roman 138 38 1,87 1,85 1,89

4. Middle Ages 140 23 1,78 1,76 1,80

properties of the ceramics shows that it is possible a separation of the pieces in the
different chronological periods of this study. Different porosities and densities of
the pieces are determined by the material composition and processing methods
employed in the ceramic manufacturing. These issues are studied in the next
section.

6.1.5.2 Ceramic Composition and Processing

The selected pieces were observed, photographed, and then analyzed using an
optical microscope and a scanning electron microscope (SEM). Some of the test
tubes prepared for SEM are shown in Fig. 6.5 .
The data provided by optical microscope and SEM show that there are clear
differences at a morphological level between the different groups of processed
fragments. Therefore, the ceramic pieces corresponding to the Bronze Age
exhibited a dark brown tone and the presence of a lot of dark-toned ferrous-
composition spots that are associated with magnetite as well as reddish ferrous iron
oxide nuclei. The Iberian ceramic pieces had varying shades between orange and
black. The quartz temper was big or very big grains and abundant ferrous iron
oxide nuclei as well as more isolated dark magnetite spots were found. This was an
iron-rich ceramic (up to 7.45 % of FeO 3 ) with a high content of calcium (up to
6.30 % of CaO). The fragments of Roman ceramic had variable characteristics
depending on the typology (sigillata, common, and amphora). In any of these, the
pieces were made of an orange-toned paste with small-size porosity and small
quantity of temper that increased from the amphora to the sigillata typology.
Roman ceramic showed content of Fe 2 O 3 of 5.71, 6.36 and 9.24 %, and content of
CaO of 0.67, 2.92 and 1.29 % for sigillata, common and amphora, respectively.
Finally, the ceramic from the Middle Ages had a bright orange to brown colour
that indicates they are made of ferrous paste. This ceramic contains abundant small
to very small nuclei of red ferrous iron oxide as well as dark-toned magnetic spots
and quartz temper of big or very big grains. Also, limestone aggregates of white
tone associated with high content of CaO (around 8 %) were observed.