The Emergence of Ceramic Technology and its Evolution as Revealed with the use of Scientific Techniques

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Energence of Ceramic Technology 1
Chapter 2
The Emergence of Ceramic Technology
and its Evolution as Revealed with the use
of Scientific Techniques
Y. Maniatis1
Introduction
From the earliest stages of his appearance on the
earth, a couple of million years ago, man began his
everlasting effort to comprehend and exploit the
environment. His aim was initially to secure his
survival and perpetuation and later the progressive
improvement of his biotic level for a more com-
fortable personal life, and a more mature social life.
From his first steps and for hundreds of thousands of
years man shapes and uses the natural materials he
finds in his surroundings, such as, stone, timber,
plants, bones, etc., for making tools, utensils, arms,
clothes and lodgings to obtain and prepare his food
better and to encounter more comfortably the
environmental conditions. The release of his hands
with the development of the erect position helped
him in such constructional attempts and at the same
time contributed to the growth of intellectual ability
that lead him progressively to the manufacture of
more and more complicated artefacts. In this long
Abstract
In the long human evolutionary course the “technology” is initially limited only in the forming
and shaping, of existing natural materials. The production of new materials like the ceramics
presents the first technological revolution in human history which occurred only in the last
9000 years. It was most probably the result of the combination of two long-existing independent
experiences; the pyrotehnology for burning limestone, and the molding of raw clay. The
scientific techniques developed and applied in the last 30 years, have lead to remarkable
discoveries about the knowledge of ancient potters. We now know how the pottery technology
developed, how the raw materials were selected and treated, how the kiln atmosphere and
temperature was controlled and how the different decoration colours and contrasts were
obtained. This paper is an account of how our understanding about the ancient ceramic
technology developed with the progressive use of scientific techniques and methodologies. It
begins with the very early attempts of potters to produced desired colours for the body and
decoration and ends with the ingenious manipulation of materials, kiln atmospheres and
temperatures to produce the high technology black and red glosses in the Classical period.
human evolutionary course the “technology” is
initially limited only in the shaping, however elabor-
ate, of existing natural materials. The production of
new materials is a relatively recent development and
began at about 11,000 years before present with the
discovery of pyrotechnology, which was initially
applied, on the manufacture of lime and gypsum
mortars (Kingery et al 1988).
However, the grand moment in the technological
development is the manufacture of the first ceramic
some 9,000 years before present in the Near East and
a bit earlier in the Far East (Rice 1987). I believe
humans achieved that by combining two long-
standing and up to that moment independent
experiences; a) their experience in pyrotehnology for
burning limestone at temperatures above 800 oC and
b) their experience in molding raw clay. They
managed in this way to produce for the first time on
earth a new material, the ceramic. The manufacture
of this new material constitutes undoubtedly the first

Y. Maniatis2
technological revolution in the human history. This
is because; man with the deliberate use of high
temperature and long time heating, managed to alter
the physicochemical properties of raw clay and thus
to produce a new hard and durable material, the
ceramic. This was an unprecedented experience and
a glorious moment in the course of human evolution.
This first technological revolution was followed by a
continuous development during which man manu-
factured progressively a lot of new materials. In the
millennia that followed the ceramic revolution we
witness the appearance of the vitreous materials
(glazed stones, faience) technology, the appearance
of metallurgy, a bit later the glass and so on. From
then onwards the technological advancement
becomes progressively faster reaching an extremely
high rate of evolution within the last 100 years when
a large range of new materials is manufactured
amongst which, are the polymers and the pure silicon
on which the modern electronic industry is based.
Despite the large variety of new materials that are
continuously produced until the present day, the
ceramics never stopped to be manufactured and
improved, being strongly associated with the course
of social and technological development until today.
The ceramic technology characterises and reflects
important parameters of an ancient cultural society,
as: 1) the organisation of the society including the
food preparation and storage, 2) the economy, 3) the
trade and commerce and 4) the connections and
competitions with other societies. For this reason the
investigation of the ancient ceramic technology is
very important and its full understanding presents a
challenge for Archaeometry
Figure 1: Stages and degrees of human intervention in the production of a ceramic vessel

Energence of Ceramic Technology 3
It is worth refreshing our minds how a ceramic is
manufactured and the degree of human intervention
in each stage. The above diagram (Fig. 1) shows the
successive stages in the manufacture of a ceramic.
The starting material is the clay, a natural sedimentary
material that existed long before the appearance of
man on the earth.
The selection of a suitable NATURAL CLAY that
contains a satisfactory percentage of argillaceous
minerals, is relatively fine and has a good degree of
plasticity constitutes the first step in the manufacture
of ceramics. The next step involves the removal from
the clay of the various accessory inactive and coarse-
grained stone fragments. This is done by levigation,
sieving and suspension in water. This process results
to an IMPROVED RAW MATERIAL, very rich in
argillaceous minerals and quite plastic. The refractory
properties of this improved raw material need to be
adjusted according to the type of ceramic product
that is going to be manufactured. This can be done by
adding, if necessary, calculated quantities of aplastic
inclusions like quartz sand or crashed pebbles,
feldspars, limestone, shells, or vegetal inclusions. A
specific quantity of water is then added and the mixed
material is manipulated either by wedging, kneading
with hands or foot treading until it is fully
homogenised and the air pockets removed. Thus the
final clay composite material ready for making pots is
ready. We can call this final regulated clay FABRIC
CLAY (Pilos). The next step involves the molding and
shaping of pilos to form the VESSEL. In the earlier
periods, the vessel was constructed by shaping a clay
lump with the hands or building it with the coil
technique and later with the help of a wheel. The
vessel could then be painted or decorated. The stage
of forming and decoration of a vessel is very important,
as in the form and decoration all parameters that
determine an ancient society are reflected. Such
parameters are: 1) the dietary habits, the needs for
storage and commerce (cultivation, accumulation of
goods, exchanges, economy), 2) the needs for social
and artistic practices, 3) the needs of religious warship
and 4) effects that emanate from possible social class
differentiations (variable accumulation of wealth,
specialisation of potters, access to raw materials, etc).
The shaping and decoration of the vessel is followed
by the firing stage. The firing causes permanent
physicochemical changes to the natural clay material.
Initially and at low temperatures (100–200°C) only
the absorbed water is evolved. As the temperature
increases (400–800°C) the chemically bound hydroxyl
(OH) water is removed; a process associated with the
disorganisation of the clay minerals. With further rise
of temperature (800–1000°C) solid-state reactions
begin to take place during which new minerals may
appear with the simultaneous formation of an
amorphous phase (vitrification), which consolidates
and cements the particles together. This whole process
converts permanently the natural clay to a CERAMIC.
The firing of ceramics requires specific skills for
reaching and maintaining firing temperatures in the
range 800–1000°C, know-how for building kilns,
control of air and it generally reflects the
technological level of a society at a specific period
and place. It is therefore obvious that the investiga-
tion of the ancient ceramic technology with modern
scientific methods provides invaluable information
on all the aspects of technological development but
also on aspects that are related with the economic,
social, and religious life of man. Methodologies for
the study of ancient ceramic technology began to be
developed in the ‘60s, based on Powder X-ray
Diffraction (Perinet 1960), Thermal Expansion (Cole
and Crook 1962; Tite 1969), optical microscopy
(Cowgill and Hutchinson 1969). In the next decade
(‘70s), new methods are added, based on Mössbauer
Spectroscopy (Bouchez et al. 1974; Janot and Delcroix
1974), Ceramic Hardness (Fabre and Perinet 1973),
Differential Thermal Analysis (Kingery 1974; Slager
et al. 1978), Porosity (Morariu et al. 1977), and
Scanning Electron Microscopy (Tite and Maniatis
1975; Maniatis 1976; Maniatis and Tite 1978/9). The
next decade (‘80s) witnessed the further development
of the methodology based on the Analytical Scanning
Electron Microscopy that was destined to dominate
the ancient ceramic technology studies. With this
method, a deeper understanding of the effects of
firing on the different types of clay used for making
ancient pottery (Maniatis and Tite 1981) and informa-
tion contributing to the qualitative and economic
elements of a society is extracted (Maniatis et al. 1988).
Today we understand most of the parameters related
to ancient ceramic technology and the techniques of
ceramic decoration and we are in a position to
appreciate the degree of difficulty, the specialisation
and the know-how that existed in the manufacture of
many types of ceramics in various periods and
cultures. This is the result of the continuous develop-
ment and systematic application of Materials Science
methodologies and the progressively accumulated
experience by dedicated archaeological scientists
(Archaeometrists). The investigation of the thermal
behaviour of raw materials in combination with the
cultural context and the absolute chronologies of the
findings has provided information not only on the
ceramic technology itself but also on the conditions
that preceded this technological revolution.
The opinion I formulated earlier, that man achieved

Y. Maniatis4
the production of the first ceramic when he combined,
at a certain moment in time, two of his long-standing
previous experiences; his art in shaping the raw clay
and his knowledge in pyrotehnology, is based on
results produced by the application of scientific
techniques. For example, it has been proved that man
had acquired the knowledge to process and mold
clay long before the firing of ceramics. In particular,
objects of refined, worked and shaped but unfired
clay, identified using X-Ray Diffraction and Analytical
Techniques, were found in various parts of the world.
Some examples are the famous clay figurines found
unfired and subsequently fired (most probably
accidentally in a destruction fire) from Dolní Vestonice
in Czechoslovakia, dating to 30,000 BC (Zimmerman
and Huxtable 1971). Also the cylindrical clay rods,
dating to 12,000 BC, from the cave Theopetra in
Thessaly, Greece (Facorellis et al. 2001) which are
considered the oldest clay objects in the Greek region.
It is certain that the evidence would have been much
richer but the clay objects being unfired cannot
survive to our days. At the same time, it has been
proven that humans, long before the manufacture of
the first ceramic, possessed the knowledge to obtain
and maintain temperatures above 800oC in large
volumes. Indeed, examination of different mortars
using electron microscopy, from settlements in
Mesopotamia, dating 10,000–9,000 BC, showed that
they consisted either of calcium carbonate (CaCO3)
or gypsum (CaSO4.x H2O) particles. The small particle
sizes (a few micrometers) and their characteristic
microcrystalline forms indicated secondary crystal-
lization in-situ on the wall after the application of the
mortar (Kingery et al. 1988). This obviously implied
combustion of natural limestone and gypsum rocks
at temperatures above 800 oC in order to evoke the
dissociation of the natural rocks and the production
of lime (Ca(OH)2) and anhydrous gypsum (CaSO4)
from which the corresponding mortars are manu-
factured. The firing of limestone and plaster requires
similar skills and logic with the firing of the ceramics;
i.e. the firing temperatures are more or less the same,
they should be uniform in large volumes (in specially
built bonfires or kilns) and they should be maintained
constant for a long time interval (a few hours).
Thus the conquest of the ceramic technology, came
as a reasonable consequence of a clever combination
of the above two long-standing and independent
experiences. For this reason the first ceramics when
they appear in Mesopotamia, are well made and fired
at suitable temperatures (850–950 o
C) to produce
enough sintering and vitrification for durable
ceramics. This has been shown by the solid-state
reactions that have occurred between the clay
minerals in their body and the development of
amorphous phase, observed by scanning electron
microscopy and X-ray diffraction (Tite and Maniatis
1975; Maniatis 1976).
Firing temperature, microstructure and
mechanical properties
There are various scientific methods that can be used
to get an estimate of the temperature at which a
ceramic has been fired (Heimann and Franklin 1979;
Tite 1995). These are based on: 1) mineralogical
changes occurring in the clay body during firing,
monitored with powder X-ray diffraction (XRD)
(Maggetti 1982), thermal expansion (Tite 1969),
differential thermal analysis (DTA), thermogravi-
metric analysis (TGA) (Kingery 1974), Mössbauer
spectroscopy (Maniatis et al. 1982; Wagner et al. 1986),
infra red spectroscopy (FTIR) (Maniatis et al. 2002),
etc, 2) Colour changes (Matson 1971) and 3) sintering
and vitrification, monitored with thin-section optical
microscopy, hardness, porosity changes and scanning
electron microscopy, or the combination of the above
methods. The firing temperature is not a strictly
defined term because the firing rate and soaking time
affects the mineralogical changes and the degree of
sintering and vitrification. It has been estimated that
firing at 960 oC with a fast heating rate of about 800 oC/
hr followed by rapid cooling, conditions similar to
that obtained in a bonfire (Shepard 1956), would
create the same effect on vitrification as that obtained
with firing at 900 oC with a slow heating rate of 200 oC/
hr and 1 hour soaking time (conditions comparable
to firing in a kiln). Thus shortening the total time of
firing from a day that is the usual situation with kiln
firings, to just 2 hours increases the effective
temperature by 60 oC (Maniatis 1976). Similar results
are obtained when the soaking time at the top
temperature decreases by 5–fold (e.g., from 300 min
to 5 min) (Norton and Hodgdon 1931; Maniatis 1976)
and when the atmosphere changes from reducing to
oxidising (Maniatis and Tite 1981). Comparable
results are also obtained for the mineralogical changes
occurring during firing at lower temperatures
monitored with FTIR, the equivalent temperature
being higher by 50–60 o
C when the soaking time
decreases by 5–fold (Maniatis et al. 2002). For this
reason it is better when one refers to firing
temperatures usually refers to the “equivalent firing
temperature”, i.e. equivalent to the heating rates and
soaking times obtained in a kiln (Tite 1999).
There are many applications on a large number of
ancient ceramic groups of different periods and
locations, through which estimates, as good as

Energence of Ceramic Technology 5
possible, of the original firing temperatures employed
have been obtained. However, it has been argued
(Gosselain 1992) that the firing temperature by itself
does not mean very much neither for assessing the
ancient ceramic technology nor for extracting cultural
and behavioural information concerning the pro-
duction and use of ceramics. Indeed, the temperature
estimation should be combined with determinations
of the chemical composition, the refractory potteries
and the tempering of the clay used. Only in this way
the level of understanding of the raw materials and
their behaviour on heating by the ancient potters can
be assessed. A method that was developed since the
mid seventies and found very interesting applications
in the study of ancient ceramic technology is the
analytical scanning electron microscope (SEM-
EDXA). This method, is based on estimating the
degree of sintering and vitrification (glassy phase)
that is observed in the microstructure of a ceramic
(Maniatis and Tite 1975; Tite and Maniatis 1975; Tite
and Maniatis 1975; Maniatis 1976; Maniatis and Tite
1981). For example, Figure 2 shows the micro-
morphology of the body of a clay vessel that has not
been fired, as seen under the SEM and at a magnifica-
tion of 2000x. The characteristic flakes of the raw clay
can be clearly seen. Figure 3 shows the microstructure
of the same clay vessel now fired at 930°C under
oxidizing conditions (all vents of kiln open). The
amorphous phase takes the form of wavy strips of
glass developing as a result of sintering and melting
of the edges of the parallel-orientated clay flakes. The
progressive sintering and vitrification helps the
adhesion and cementing of the particles together, a
process, which converts the natural clay to a ceramic.
The development of scanning electron microscopy
in combination with microprobe X-ray analysis
contributed a lot to the understanding of the effect of
firing on natural clays and the factors that influence
the progressive changes in their microstructure. It is
now known that the sintering of clays during firing
occurs with the transfer of material to the contact
surface between the particles (Fig. 4a) through a
process of “plastic flow” (mobilization of molecules
without full melting) (Kingery et al. 1976). The
development of a glassy phase (vitrification) is
independent of the sintering. However, the appear-
ance of the vitreous “liquid” phase increases the
surface tension between the clay particles and this
creates a lower pressure in the contact surface and
hence the appearance of attractive forces that draw
the particles together (Fig. 4b) leading to the familiar
contraction of the ceramics during firing. Vitrification
appears as continuous glass filaments at first, joining
the edges of the parallel aligned clay particles and
later as wavy glassy strips (Fig. 4b) when the filaments
from several clay layers fuse together. This process
Figure 2: SEM backscattered electron image of an unfired
clay vessel (fractured surface). The clay flakes can be clearly
seen.
Figure 3: SEM backscattered electron image of clay vessel
fired at 930 oC (fractured surface). The vitrification in the
form of smooth glass wavy strips is evident
Figure 4: Layers of clay flakes aligned parallel as in a clay
vessel, a) during heating material flows to the contact edges
of the particles, b) melting occurs at the edges creating
wavy strips of glass. The particles are drawn together
resulting in sintering and contraction.

Y. Maniatis6
can be monitored very precisely with the SEM as can
be seen in Figure 3. The temperatures at which the
above changes occur, the amount of glassy phase
developed, the pattern the vitrification exhibits in
the clay matrix and the degree of contraction, depend
on the chemical and mineralogical composition, and
the particle sizes. It also depends on the amount,
type and size of accessory minerals and aplastic
inclusions. Figures 5a and 5b, show the dramatic
differences, revealed with the SEM, in the
microstructure between a ceramic made of a low in
calcium (CaO = 0–2 %) clay and a ceramic made of a
clay high in calcium (CaO = 15%), both fired at the
same temperature (1000 oC). The calcareous ceramics,
containing CaO > 6% in a fine calcium carbonate
form, exhibit a characteristic cellular structure with a
high porosity (Tite and Maniatis 1975) and in the
same time the vitrification is more restricted and
controlled up to 1150°C. This characteristic micro-
structure remains constant for 200°C (850–1050°C)
and above that there is a progressive increase of
vitrification, the glass phase becoming grainy and
highly viscous (Tite and Maniatis 1975; Maniatis
1976). Contrary to that, the non-calcareous clays,
containing CaO < 6%, produce a much more vitrified
ceramic body with a high density and impermeable
to fluids. Furthermore, due to the extensive and rapid
vitrification the non-calcareous ceramics collapse at
temperatures approaching 1100°C (Maniatis 1976).
The calcareous ceramics have a greater resistance to
thermal and mechanical shocks due to their highly
porous microstructure (Kingery et al. 1976), as the
energy is absorbed by the voids, but they have lower
resistance to loading and compression, as they are
less rigid.
Hence, the examination of the ceramic micro-
structure under the analytical SEM provides informa-
tion on the degree of vitrification that leads to the
estimate of the firing temperature but in the same
time on the chemistry and type of clay used and its
refractory properties (Maniatis and Tite 1981).
Important information is thus extracted on the level
of apprehension by the ancient potters of the
properties of different clays. This in combination with
the raw material availability in a certain region and
its use for specific types of ceramic ware leads to a
deeper understanding of the level of ancient ceramic
technology and the social and economic implications
related with it (Maniatis et al. 1988; Tite 1999).
The mechanical and thermal properties of
ceramics can be modified strongly by introducing
aplastic inclusions whose concentration and size
affects strongly these properties. Such inclusions may
be fragments of quartz, feldspars, limestone, seashells
etc. Their role is quite important in preventing
extensive cracking by the stresses developing during
the drying shrinkage, especially in thick walled
vessels like pithoi, but also increase the toughness
(prevent breakage by cracking) of the ceramic during
loading. Figure 6a and 6b show in diagrammatic form
how the cracks developing initially in the vicinity of
an inclusion (Fig. 6a) are widened during drying (Fig.
6b). The energy of the widened cracks is absorbed in
the void of the inclusion, which in this way prevents
the cracks extended from one surface of the vessel to
the other. In the same way a crack propagating in a
ceramic, containing quartz inclusions, by bending is
absorbed and its propagation stopped by the
inclusions (Fig. 7). The role of inclusions in the
mechanical and thermal properties of ceramics has
Figure 5 (a): SEM backscattered electron image of a non-calcareous ceramic fired at 1000 oC (fractured surface) – Totally
vitrified matrix. (b): SEM backscattered electron image of a calcareous ceramic fired at 1000 oC (fractured surface) – An
open cellular porous matrix

Energence of Ceramic Technology 7
been the subject of extensive research in recent years
(Kilikoglou et al. 1998; Vekinis and Kilikoglou 1998;
Tite et al. 2001).
Colours of body and paint in oxdising
conditions
The systematic applications of microanalysis,
mineralogical studies and Mössbauer spectroscopy
in combination with magnetic measurements con-
tributed greatly to the better understanding of the
parameters controlling the colour differences
between the different ceramics and the utilization of
these properties by the ancient potters to produce
various aesthetic and functional results. It is now
known that the colour exhibited by a ceramic is a
result of the chemical composition of the clay and the
firing conditions (temperature and atmosphere). The
iron oxides play a very important role in the colour
of the fired ceramic and influence also the colour of
the natural raw clay. Initially in the raw clay, iron is in
the form of iron hydroxides, such as, FeO(OH), that
are orange or brown in colour and fine iron trioxide
(Fe2O3), which is red/brown in colour. Some Fe is also
bound in the form of ions Fe3+ or Fe2+ in the structure
of the clay minerals that are colourless. The com-
bination of the different forms and quantities of iron
existing in a clay together with the quantity of organic
material contained gives a variety of colours to the
raw clays which range from grey, beige, brown,
orange, or red.
When a clay is fired the colours change depending
on the temperature and atmosphere, but the presence
of fine calcium carbonate in the raw clay plays again,
as in the development of micromorphology, a very
essential role to the final colour. In non-calcareous
clays fired at oxidising atmosphere (all vents of kiln
open) there is a progressive crystallisation of Fe in
the form of alpha-Fe2O3 (hematite), which is red in
colour. These oxides grow in size and quantity as the
firing temperature increases above 700°C at the
expense of the Fe-hydroxides and the Fe-ions in the
clay mineral lattice, which begin to disorganise and
dissociate above that temperature liberating Fe ions
(Maniatis et al. 1981; Maniatis et al. 1982; Maniatis et
al. 1984). As a result, the non-calcareous clays fired at
oxidising atmospheres exhibit red colours, which
become more intense as the firing temperature
increases. Contrary to that, the reactions occurring
during firing in the calcareous clays (fine CaO > 6%)
are quite different. The CaO that appears from the
dissociation of calcium carbonate above about 750–
800 oC, reacts strongly with the iron oxides and breaks
them down. This leads to the decrease in the size and
amount of Fe-oxide particles and hence to the
bleaching of the red colour to pink, cream or even
whitish as the temperature increases above 850°C and
according to the original amount of calcium carbon-
ate in the clay. The Fe which is liberated from the
dissociation of iron oxides participates in the crystal-
lisation of new calcium aluminosilicate minerals
(Maniatis et al. 1981) which stabilise the micro-
structure of the calcareous clays for 200°C (850–
1050°C). These new minerals are colourless. Excep-
tions to this general behaviour do occur. For example
there are calcareous clays that they are red from the
beginning and remain red after firing, because the
original amount and particle size of the iron oxides
Figure 6: Crack propagation, a) cracks propagate to the
inclusion, b) cracks become wider during drying but their
energy is absorbed around the void of the inclusion.
Figure 7: Crack created and propogating (from left to right
under mechanical bending in a ceramic containing quartz
inclusions.

Y. Maniatis8
present is so large that the CaO is not enough to react
to a considerable degree as to bleach the colour
(Maniatis et al. 1981), equally there are some non-
calcareous clays that fire to whitish colours because
the initial amount of iron oxides they contain is very
small. The latter are usually the high refractory
kaolinitic clays (Maniatis and Tite 1978/9).
These colour differences between the various clays
were cleverly utilised by the ancient potters from the
Neolithic times. They used these different clay
properties in order to produce decorative colour
contrasts with a single firing. An example is shown
in Figure 8 where a beautiful red coloured decoration
has been applied on a buff coloured body. This result
was achieved by using a highly calcareous clay for
the body and a non-calcareous fine clay for the
decoration paint and fired in an oxidising atmosphere
at a temperature of 900°C. Judging from the final
fired colours and based on recent experience accu-
mulated on various raw clays one can say with a fair
degree of certainty that the initial raw colours for the
two clays used for this vase in Figure 8 must have
been; light grey for the body and orange or red for
the paint. The manufacturing of such a vase required
a selection and refinement of raw materials, as well
as uniform oxidising firing, facts that are associated
with production of high quality pottery. Pottery of
the same kind, with red “flame-like” decoration on
buff body, was found in the Middle Neolithic period
at Sesklo, Thessaly among other monochrome vases.
The scientific investigation using analytical SEM,
showed that this pottery was indeed of high quality
requiring the use of a special calcareous clay that was
not available in the immediate vicinity of the site and
a specially treated non-calcareous clay for the red
decoration. Furthermore, this pottery was fired at
such conditions as to take full advantage of the
specific clay properties. The same was not true for
the rest of the pottery found at the site or in a nearby
site (Sesklo B) that was dominated by the mono-
chrome lower quality pottery (Maniatis et al. 1988).
Therefore, this high quality pottery required skilful
and specialized potters most perhaps not producing
their own food, probably implying a central economic
system that distributed the wealth (Kotsakis 1983).
Colours in reducing conditions
Firing pottery in reducing conditions (lack of oxygen
and presence of reducing gasses, such as CO in
smaller or larger amounts) produces different results.
The Fe-hydroxides and Fe-oxides existing in the raw
clay dissociate during firing under reducing con-
ditions above about 700°C and by liberating oxygen
they are progressively converted to magnetite (Fe3O4)
or wustite (FeO) or even rarely to metallic iron
depending on the intensity of the reducing conditions
and the firing temperature. Both magnetite and
wustite are black in colour while metallic iron has a
dark metallic shade. Furthermore, wustite is a very
strong flux and its presence in the clay matrix at
temperatures above 800°C can lead to intense solid-
state reactions with the argillaceous clay minerals.
This results to an increased vitrification and rapid
drop of the viscosity of the glass phase. The dropping
glass viscosity in combination with the liberation of
oxygen from the dissociating iron oxides creates
bloating in the microstructure. The bloating pores
clearly seen with the SEM (Maniatis and Tite 1975)
increase in size with the firing temperature and this
leads very soon to the swelling and deformation of
the vase and finally to its collapsing. Thus the
conversion of iron oxides from their oxidized form to
the reduced one produces in general dark ceramics
and glass with low viscosity and bloating.
However, this is not always the case. The presence
of fine calcium carbonate in the clay is again very
important for the properties of the ceramic such as
microstructure, vitrification, bloating and the final
colour. In the non-calcareous clays firing in a reducing
atmosphere produces dark grey to even black colour
ceramics, while in the calcareous ones reducing firing
produces light grey to even whitish colours. The
difference is due to the fact that in the calcareous
clays the CaO reacts with the Fe-oxides and as in the
case of the oxidising conditions forms new Ca-Fe-
aluminosilicate minerals (Maniatis et al. 1983). This
absorption of Fe into new minerals does not favour
the crystallisation of the reduced black iron oxides
Figure 8: Red on buff decoration on a Neolithic Period
vessel from Thessaly, Greece.

Energence of Ceramic Technology 9
(magnetite and wustite), and so the colours of the
calcareous ceramics fired in reducing conditions
range from pale grey to whitish (CaO > 15–20%)
according to the initial amount of calcium carbonate
and the firing temperature. The decrease in the
production of FeO in the calcareous ceramics, apart
from the colour, has an important effect in the
properties of these ceramics. The uncontrollable
production of low viscosity glass in the micro-
structure is stopped and the bloating is largely
reduced (Maniatis and Tite 1975) preventing in this
way the deformation and the collapsing of the vessel,
even at higher temperatures.
For the colour of ceramics fired in reducing
conditions, it should be noted that the differences
between calcareous and non-calcareous clays emerge
only above 800°C, because the dissociation of CaCO3
and the appearance of the reactive CaO in the clay
matrix occurs at about this temperature. Firing at
temperatures below 800°C does not produce any
difference in the colour or the properties of the
ceramics. The colours in this case are all dark grey
irrespective of the clay chemistry. Figure 9 shows an
indicative diagram for the colours developing in
calcareous and non-calcareous ceramics during firing
in a reducing atmosphere. The curve of non-
calcareous clays is only theoretically extended to
1100°C, because as discussed above such a ceramic
cannot survive above 950°C in reducing conditions.
However, when a non-calcareous clay is heavily
tempered it can resist higher temperatures in
reducing conditions. An example are the high density,
strong and impermeable bodies of a class of dark
coloured Punic Amphorae found at Corinth (5th
century BC), containing quartz, feldspar, mica schist
but also some limestone inclusions. (Maniatis et al.
1984).
The reducing conditions during firing of the
ceramics can be created by closing all the openings
of a kiln and throwing some fresh wood in the fire
compartment or by firing in ground pits and covering
all the vessels with straw and wood or with larger
vessels (pithoi). Sometimes reducing conditions can
be created at a certain point inside a kiln or a bonfire
accidentally due to bad air circulation. A lot of dark
coloured ceramics, some nicely burnished, are
observed in the Neolithic and Early Bronze Age
Period in many parts of the world and it is the result
of firing in ground pits covered with straw, wood
and perhaps soil on top. These vessels are typically
made of non-calcarous clays and fired at about 800°C
or even sometimes of calcareous clays but fired below
800°C so that the calcium carbonate does not dis-
sociate. The reducing firing is surely intentional and
the dark coloured ceramics represent a certain
tradition. However, the firing conditions are not easily
controlled and for this reason a lot of ancient ceramics
are partially grey and partially red (Fig. 10). At about
the Middle Bronze age in Greece (1900 BC) grey
uniform ceramics fired in reducing atmosphere but
Figure 9: Diagram indicating the development of colours in non-calcareous and calcareous ceramics fired under reducing
conditions.

Y. Maniatis10
certainly in kilns are produced in many parts of
Greece. Typical examples are the so-called “Grey
Minyan” ceramics (Fig. 11), the best of which are
made of a highly calcareous clay, fired at about 950
oC. They have a uniform light grey colour and a
characteristic soapy feel due to the very fine
calcareous clay from which they are made.
Black decoration on a light background
The black decoration on a light body (red, pink, crème
or white) represents a further advancement in
ceramic technology. In order to produce a red or light
colour body the ceramic needs to be fired under
oxidising conditions. In this case however, if the
decoration paint were made of a fine clayish material
its colour after an oxidising firing would be red or
pink, like the example of Figure 8. Thus, in order to
achieve a black decoration on a reddish or whitish
body a material other than clay should be used. This
material must be black and should stay black after
firing in an oxidising atmosphere.
Typical materials for this technique are the natural
manganese ores used during the Neolithic and Early
and Middle Bronze Age (Noll 1982). Such ores are
the MnO2 either in pure crystalline form called
pyrolusite or in a colloidal form known as
psilomelane, the latter sometimes containing also
barite (BaSO4). These manganese oxides are originally
black and remain black after firing in oxidising
conditions. Sometimes Fe-Mn ores are used which
also contain small quantities of clay (Noll et al. 1975;
Aloupi and Maniatis 1990; Kilikoglou et al. 1990),
which helps to adherence better the paint on the
vessel’s surface. In this case the colour of the decor-
ation at higher temperatures can come out dark
brown rather than black. Using therefore manganese
oxide pigments for the decoration it is relatively easy
to obtain the contrast of a black or dark brown
decoration on a light body. The body can be made of
calcareous clay and the vessel fired in oxidising
conditions at temperatures in the range 800–900 o
C.
Using the manganese oxides polychrome decorated
vessels could also be obtained (Fig. 12). In this case
manganese oxide is used for the black decoration,
non-calcareous refined clay for the red decoration
and calcareous clay for the body (Aloupi and
Maniatis 1990; Kilikoglou et al. 1990). A single firing
at an oxidising atmosphere is enough to produce this
polychrome result. However, the black coloured
decoration obtained with manganese pigments is not
in general of so good quality, because it is relatively
coarse and does not sinter in the usual firing tempera-
ture ranges (850–1050°C). As a result the paint has a
mat appearance without any sheen, despite the
polishing efforts obvious in some cases and has a bad
adherence with the body being rubbed off by the
hand quite easily.
During the end of the Middle Bronze Age but
especially during the Late Bronze Age, a black paint
of a much superior quality appears produced with
the so-called iron reduction technique involving the
reduction of iron oxides in the paint. The under-
standing and deliberate use of this technique by the
ancient potters represents a big step forward in the
ceramic technology evolution. For the production of
this black paint a very good control of the kiln is
Figure 10: Neolithic dark coloured (dark burnished) vessel
made of non-calcareous clay fired in reducing conditions at
about 800°C. The bottom part is either intentional or
accidentally oxidized.
Figure 11: Middle Bronze Age ‘Minyan pottery” made of
a highly calcareous clay fired in reducing conditions at
about 950°C. Compare the light grey colour due to the
presence of CaO with the dark of figure 11.

Energence of Ceramic Technology 11
required with a precise closing and opening of the
vents in order to change the atmosphere in the kiln
from oxidising to reducing and then back to oxidising
at specific temperatures and times. In this way a black
glossy decoration is produced on a light body back-
ground. With the application of scientific techniques
it was made possible to reveal the complicated
technology involved in the manufacturing of the
black gloss decoration, using the iron reduction
technique (Hofmann 1962; Noll et al. 1975; Tite et al.
1982; Aloupi and Maniatis 1990; Kingery 1991; Aloupi
1993; Maniatis et al. 1993), and to establish that this
technique reached an extremely high level of tech-
nology during the Classical Period in Attica. This was
the period when the famous Attic Black Figured and
Red Figured vases (Fig. 13) were manufactured and
acquired a very high artistic and commercial value
being traded all over the ancient world of that period.
The analytical scanning electron microscopy proved
once again a powerful tool for the extraction of
invaluable technological information. Figure 14
shows the micromorphology of the black gloss paint
and the ceramic body of an Attic vessel at a cross
section. The black gloss layer exhibits a high degree
of uniformity and sintering. The amount of vitrifica-
tion is optimum so that the layer is quite dense and
perfectly bonded to the body but at the same time
does not show any deformation or bloating. The
ceramic body exhibits an open cellular micro-
structure characteristic of a calcareous clay fired in
the range 850–1050°C. In the next figure (Fig. 15) one
can see the micromorphology of black paint from
earlier periods (LBA), when the first attempts to
produce black paint on light body using the iron
reduction technique begun (Aloupi and Maniatis
1990). The differences with the attic black gloss are
apparent. The vitrification of the LBA black layer is
excessive; the viscosity of the melted paint has
dropped dangerously with the simultaneous appear-
ance of bloating and deformation, resulting to a lower
quality product. Actually, this outcome is the most
frequent result when there is no absolute control on
the firing conditions in the kiln (atmosphere and
temperature) or/and on the selection and treatment
of the raw materials.
A comparison of the chemistry between black
glosses of different periods, from Early Bornze Age
to the Classical period (Table 1) shows the improved
refinement of the paint material with time as wit-
nessed by the progressive removal of Ca and the
increased ration of Al/Si, from 0.45, to 0.61 and finally
to 0.67 in the classical period.
For the high quality black gloss paint, like the one
on the Attic vases, a carefully selected and thoroughly
Figure 12: Vessel from Akrotiri, Thera bearing Mn-black
decoration. The red decoration is made of fine non-
calcareous clay. The body is made of a highly calcareous
clay. It is fired in an oxidizing atmosphere.
Figure 13: Red figured attic vase. The black paint is
produced with the iron reduction technique.

Y. Maniatis12
treated clay is needed, as well as, a fully controlled
three-stage firing. The raw material to be used for the
paint should be practically free of calcite (CaO < 1%),
enriched in fine clay minerals, potash and iron oxides.
This can be achieved by the selection of a fine illitic
and calcium free clay and then by a persistent
suspension in water for months. During the pro-
longed suspension the aplastic and coarser particles,
like quartz, feldspars, aggregates etc., are removed
and the suspended fraction is enriched in very fine
argillaceous minerals (mainly illite) and very fine iron
hydroxides or/and iron oxides that give to the raw
paint an orange to red initial colour. The selection
and treatment of the raw materials can be seen in
Figure 16 that shows the iron concentration;
important for the colour, against the Al/Si ratio that
indicates degree of refinement. The consistency in
chemistry and treatment is remarkable, particularly
for the black gloss paint.
The examination of the black gloss paint on attic
vases with the transmission electron microscope
(TEM), at high magnifications, gave important
information on the grain sizes and the firing con-
ditions (Maniatis et al. 1993). The black paint seems
to contain mainly magnetite (Fe3O4) crystals, as was
verified with electron diffraction, that are dispersed
inside an amorphous matrix (Fig. 17). Magnetite has
a black colour and its presence gives the paint its
characteristic black colour. As was discussed earlier,
magnetite does not exist in the raw clay but it is
produced from the dissociation of hematite during
firing in reducing conditions. It is therefore clear that
at some stage of the firing the atmosphere in the kiln
was reducing. Furthermore, the affluent presence of
magnetite suggests that the reduction stage was mild
and controlled so that the dissociation of hematite
practically stopped after conversion to magnetite and
did not progress further to produce large quantities
of FeO. The latter is very reactive and if present would
lead to rapid vitrification with inevitable bloating and
deformation as in Figure 15. Contrary to the reducing
firing verified for the black paint, the ceramic body is
fired in oxidising conditions as is deduced from its
pink colour. These results clearly indicate an alterna-
tion in the kiln’s atmosphere from oxidising to
reducing and vice-versa. As far as the grain sizes of
the paint material is concerned, the greatest size of
original particles typically found in the attic black
gloss are some rare titanomagnetite particles (a rather
common aplastic accessory mineral in a lot of clays)
of dimensions 0.0003 mm (Maniatis et al. 1993). Thus,
from the TEM examination it is confirmed that the
refinement of the clay used for the paint was
extremely persistent.
The above scientific conclusions inferred from the
examination and analysis of the attic black gloss were
tested thoroughly with simulation experiments in the
laboratory (Aloupi 1993). These experiments sug-
gested that the optimum three-stage firing cycle must
had been as follows:
Stage 1: Initial firing in oxidising conditions up to
about 900 oC and soaking at top temperature for
an hour or more.
Stage 2: At the top temperature creating reducing
conditions by closing all the vents of the kiln and
feeding the fire with fresh wood, most probably
Figure 14: Micromorphology of the black gloss of an attic
red-figured vase (6th cent. BC) at a cross section near the
surface. The unique homogeneity of the sintered and
compact black gloss layer adhering nicely to the porous
calcareous body is evident. SEM image at backscattered
electron mode.
Figure 15: Micromorphology of a much earlier (1600–1500
BC, Thera) black paint produced with the iron reduction
technique, at a cross section near the surface. The black
layer is grainy, with bloating porous and deforming. The
body is again calcareous and porous. SEM image at
backscattered electron mode.

Energence of Ceramic Technology 13
wet. Inevitably and wilfully the temperature drops
a couple of hundred degrees to about 700–750 oC.
Stage 3: Opening again all the kiln’s vents and new
increase of temperature up to about 850 oC for an
hour and then cooling, maintaining the oxidising
conditions until the end.
In the first oxidising stage, the body of the ceramic
becomes pink since it is made of calcareous clay. The
paint becomes intense red as it contains no calcium
carbonate and it is rich in iron, the latter forming
well-crystallised hematite particles. At this stage a
controlled sintering and densification occurs in the
paint layer.
In the second stage that is reducing, hematite is
transformed to magnetite and as a result the colour
of the paint becomes intense black. The body colour
becomes grey as all calcareous clays (see diagram of
Fig. 9). This stage is very critical because if the control
on temperature or atmosphere is lost to more intense
Table 1: Comparison of average chemical compositions of black gloss in Early Bronze Age and Attic Pottery. Concentrations
expressed as % oxides (Fe as FeO) (Aloupi and Maniatis 1990; Aloupi 1993; Maniatis et al. 1993).
Black gloss Na Mg Al Si P S Cl K Ca Ti Mn Fe Al/Si
EBA, Thera 1.4 2.6 22.0 48.7 0.5 0.3 0.1 5.9 4.4 0.5 0.3 18.3 0.45
Late Geometric, Naxos 1.9 2.9 26.9 44.0 0.3 0.2 0.3 6.2 1.9 0.6 0.2 14.7 0.61
Archaic Period, Attic 1.0 2.6 28.9 45.4 0.2 - 0.1 6.1 1.0 0.7 0.1 14.2 0.64
Classical Period, Attic 0.7 1.9 30.3 45.2 0.4 0.1 0.1 5.3 0.6 0.7 0.1 14.9 0.67
Figure 16: Fe concentration plotted against the ratio Al/Si for the body and the black gloss of a number of attic pottery of
the 6th and 5th century BC.
Figure 17: Micromorphology of attic black gloss under the
transmission electron microscope at high mignifications
(75,000 x). The black grains are magnetite or hercynite
particles, their typical electron diffraction pattern is shown
on the top right-hand corner (Maniatis et al. 1993).

Y. Maniatis14
reducing conditions, magnetite may dissociate
further to wustite leading to rapid vitrification and
melting of the paint layer as discussed earlier. On the
other hand if the atmosphere swings to partially
oxidising hematite would not be fully converted to
magnetite resulting to brown rather than black
colours. There are a lot of examples of both cases of
failed black gloss in antiquity. The controlled reduc-
tion at this stage produces the optimum degree of
sintering and vitrification so that the paint layer
becomes compact and impermeable to gasses,
excluding in this way any diffusion of oxygen into it
and proxibiting the re-oxidation of magnetite at the
final oxidising stage.
At the third stage, a re-oxidation of the porous
body occurs and its colour is reinstated to a great
degree to the initial pink/reddish colour of the first
stage. However the paint layer is impermeable and
cannot be re-oxidised (if the reducing conditions are
right, as explained above), remaining black and stable
until the end of the firing cycle.
Figure 18 shows approximately the colour changes
occurring in the body and paint during the various
firing stages for producing a black glossy decoration
on a pink or light red body, as that observed on the
red-figured or black-figured attic vases. The surface
of the vessel made of a calcareous clay is wiped with
a wet sponge to make the surface smooth. The colour
of the raw body clay was almost certainly grey, as all
the natural fine calcareous clays that can be found in
Greece. The decoration that is going to come out black
is painted with the specially refined clay, as discussed
earlier. The initial raw colour of the paint material
was either orange or red due to its enrichment in iron
oxides. The difference in colour of the raw clays
between body and paint helped the artist to paint the
decoration details, which in some cases were
extremely fine. The rest of the surface was not covered
with any other slip or material in order to remain
porous and facilitate its re-oxidation during the final
oxidising firing stage.
Concluding for the black gloss paint on the Attic
vases, the selection and extremely high refinement of
the raw materials and the control of the kiln during
the complicated three-stage firing is reflecting a very
high technology level. It surely denotes an important
technological achievement at the end of a progressive
development for about 1000 years from the date it
was first tried in MBA about 6000 years after the first
appearance of ceramics. This manufacturing know-
how in conjunction with the beautiful in most cases
angiographies gave these vases a very high trading
value.
Red gloss in conjunction with black gloss
There are some Attic vessels, although very rare,
bearing simultaneously black and red gloss
decoration on a pink or light-red body. The term red
gloss refers to a red sintered and glossy paint having
more or less the same appearance as the black gloss
except that it is red in colour. This paint was
sometimes called “intentional red glaze” (Farnsworth
and Wisely 1958) in order to signify the fact that it
was a paint designed to come out of the firing red
and glossy, and it is not a failed black gloss or a
background red colour. The intentional red gloss
should not be confused with the so-called “accessory
red” which is a coarse matt paint of a purple colour.
Given the fact that the red gloss paint layer is sintered
and may block the entry of oxygen at the last
oxidising firing stage, its presence on a ceramic
surface together with the black gloss presents a
challenging technological achievement and makes its
scientific investigation quite interesting.
Some researchers (Richter 1951) had suggested that
the paint for the red gloss was applied after the first
three-stage firing that produces the black gloss and a
second purely oxidising firing was necessary for the
red gloss. One of the earliest scientific investigations
of the intentional red gloss combined also with
reproduction experiments was in 1958 (Farnsworth
and Wisely 1958). They suggested that a second firing
was not necessary. The intentional red was made from
the same clay used for the black gloss by adding to it
some quantity of very fine ochre prepared in a
suspension. The added ochre delays sintering and
Figure 18: Diagram showing the colour changes during
the three-stage firing for the production of the attic black
gloss.

Energence of Ceramic Technology 15
vitrification, thus, both paints were applied on the
vessels when the body was in a leather-hard state and
a single three-stage firing was performed. During this
firing the black sinters and becomes a coherent solid
mass as discussed before, while the ochre-containing
glaze remains porous and is easily reoxidised at the
last oxidising stage. More recent work (Tite et al. 1982)
using scanning electron microscopy suggested that
addition of ochre to the red gloss cannot be verified
by analysis and microscopic examination. However,
the more porous texture of the red gloss that would
allow reoxidation during the final oxidation firing
stage was verified. This according to the authors could
be obtained by collecting a fine but slightly coarser
fraction from the suspension during the refining
process to prepare the black paint. Using these two
fractions the black and red gloss can be produced
simultaneously at a single three-stage firing.
New analysis and examination of the intentional
red gloss on attic vases of the 6th and 5th century
which is under progress at the Laboratory of
Archaeometry, NCSR “Demokritos” is providing
interesting but a bit puzzling new evidence. The
intentional red gloss seems to have at least two
versions. The 5th century sample, called also “coral
red” contains a higher amount and particle size
distribution of iron oxides and the degree of
refinement of the original clay (Al/Si = 0.60) is less
than that of the black gloss (Table 1). This could well
had been produced by adding ochre to the paint
prepared for the black gloss. It is most probably the
type of “intentional red” examined by Fansworth and
Wisely (1958), so their suggestion makes sense. On
the contrary, our 6th century sample is of a very
different nature. The chemistry and microstructure
are very similar between black and red (Table 2). This
agrees more with the samples examined by Tite et al
(1982), but only as far as the similarity in chemistry
between black and red gloss is concerned. As far as
the microstructure is concerned, in our case they are
identical between black and red (Kavoussanaki 2002).
Figures 19 and 20 show SEM micrographs of polished
sections of black gloss and red gloss on the same attic
vessel. They exhibit the same size and distribution of
iron oxide particles (white spots) and same degree of
sintering. This similarity makes it very difficult to
understand how the red paint layer could have been
re-oxidised but the black could not. One wanders if
there is any minute porosity differences, undetectable
with the SEM that could perhaps explain the re-
Figure 19: Black glass of attic vessel – polished section.
SEM backscattered image. White bar corresponds to
0.01mm.
Figure 20: Red gloss – polished section the same attic vessel
as Figure 19. SEM backscattered image. White bar
corresponds to 0.01mm.
Sample Na2O MgO Al2O3 SiO2 K2O TiO2 FeO Al/Si
Black Gloss 0.74 1.40 31.14 46.48 4.78 0.49 14.99 0.67
Red Gloss 0.77 1.49 31.62 45.37 4.63 0.55 15.00 0.69
Coral Red 1.77 1.89 27.68 46.29 3.47 1.25 16.88 0.60
Accessory Red (Purple) - - 5.88 34.34 2.39 0.56 54.05 0.17
Table 2: Examples of the basic chemistry of various Attic red paints co-existing with black gloss.

Y. Maniatis16
oxidation of the red paint at the final firing stage
however, it has to be proven by further investigation.
The possibility of a second firing in oxidising
atmosphere just for the red, using exactly the same
paint material as for the black, must be excluded as
the optical microscope examination reveals a black
zone in the red gloss paint at its innermost side (Fig.
21). This black zone is clear evidence that this paint
has undergone a reducing cycle at an intermediate
stage, the density of which been such that it was not
fully re-oxidised, down to the deepest layer close to
the vase body, during the final oxidizing stage. A
paper presenting these new experimental results is
under preparation.
Conclusions
I hope this paper has shown the invaluable con-
tribution of scientific techniques in the study of
ancient ceramic technology. This was the result of
systematic and dedicated work by several archae-
ometrists during the last few decades, one of them
being undoubtedly M.S. Tite. Important information
on various aspects of ceramic technology has been
extracted from the moment of its emergence till recent
times. We now know the role of clay chemistry and
firing properties of the different natural clays and the
effect of treatment of the raw materials. We also know
that ancient potters progressively understood better
and deeper the parameters influencing the physical
and chemical properties and quality of the final
product. Through the selection of suitable materials,
teh modulation of their properties by ingenious
treatment and clever manipulation of the kiln con-
ditions the ancient potters reached an extremely high
level of ceramic technology in classical times. This
was followed by the development of transparent
glazes and porcelain. The scientific investigation of
ancient ceramic technology has allowed the under-
standing of the technological solutions adopted in
each period and place and has shed light on the
techniques used for the production of most known
types of ceramics all over the ancient world.
Archaeologists have realised the importance of
these new developments and collaborate systematic-
ally with archaeological scientists for ancient ceramic
technology studies. A number of them are engaged
themselves in scientific examination and have
acquired experience in reading and interpreting the
scientific results. We have gone far beyond the earlier
times when archaeologists described the pottery only
by body form and style of decoration and the times
when they believed the different ceramic colours
observed were solely due to different clays used; been
totally unaware of the dramatic effects on the colour
of the firing temperature and atmosphere.
It is now clear that the full understanding of
ancient ceramic technology and its social and eco-
nomic implications can only be obtained through an
integrated approach. This involves the investigation
of the system: Clay selection and refinement –
refractory properties – firing temperature and atmo-
sphere – mechanical and thermal properties –
decoration technique – availability and provenance
of raw material – social context and use.
There is still a lot to be learned, many different
types of ceramics to be investigated but the most
important goal has been already achieved. This is the
set of unique developed methodologies and back-
ground knowledge obtained by the previous archae-
ometric generation. These are now inherited to the
younger researchers of the field and allow the
integrated study of any group of ceramics and the
assessment of the level of technology and know how
at any period or area.
Note
1 Laboratory of Archaeometry, Institute of Materials Science,
NCSR “Demokritos”, 153 10 Aghia Paraskavi, Attiki, Greece,
e-mail: maniatis@ims.demokritos.gr
Figure 21: Optical microscope picture of polished cross
section of intentional red gloss. The inner part of the paint
layer is black indicating a preceding reduction stage and
not full reoxidation during the final firing stage
(magnification 100 x).

Energence of Ceramic Technology 17
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