Lead-Glazed Ceramic Fragments: Intentional Glazing or Metallurgical Accident?

Abstract

Ceramic fragments from an excavation by Landschaftsverband Westfalen-Lippe in 2014 around the deserted early medieval site of Brilon-Alme were subjected to archaeometric analysis. Except for one miniature object, they are coarse-grained tempered, and many of them are coated with a green-brownish glaze. The question arose whether archaeometric investigation could help identify the material, the production technique, and the nature of the glaze. Furthermore, it was of interest whether the fragments were connected to metallurgical activity in the region. Thin sections of the fragments with adhering glaze were investigated by polarized light microscopy and energy-dispersive scanning electron microscopy, both for elemental information; powder and x-ray microdiffraction for phase analysis and multi-collector inductively coupled mass spectrometry for lead isotope analysis were applied. The results from elemental, phase, and texture analysis of the glazes finally provided evidence that they are closely related to metallurgical processes of early medieval activities around Brilon.

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Metallography, Microstructure, and Analysis
https://doi.org/10.1007/s13632-023-00944-4
PEER-REVIEWED PAPER
Lead‑Glazed Ceramic Fragments: Intentional Glazing orMetallurgical
Accident?
S.Klein1,2 · S.Fischer‑Lechner1,2· C.Berthold3· J.Sessing4· T.Kirnbauer5 · M.Zeiler6· W.Essling‑Wintzer7
Received: 18 September 2022 / Revised: 13 February 2023 / Accepted: 3 March 2023
© The Author(s) 2023
Abstract
Ceramic fragments from an excavation by Landschaftsverband Westfalen-Lippe in 2014 around the deserted early medieval
site of Brilon-Alme were subjected to archaeometric analysis. Except for one miniature object, they are coarse-grained tem-
pered, and many of them are coated with a green-brownish glaze. The question arose whether archaeometric investigation
could help identify the material, the production technique, and the nature of the glaze. Furthermore, it was of interest whether
the fragments were connected to metallurgical activity in the region. Thin sections of the fragments with adhering glaze
were investigated by polarized light microscopy and energy-dispersive scanning electron microscopy, both for elemental
information; powder and x-ray microdiffraction for phase analysis and multi-collector inductively coupled mass spectrometry
for lead isotope analysis were applied. The results from elemental, phase, and texture analysis of the glazes finally provided
evidence that they are closely related to metallurgical processes of early medieval activities around Brilon.
Keywords Archaeometallurgy· Lead· Glaze· Pottery· Kiln· Brilon· Melanotekite· Hematite· Micro-XRD
Introduction
Geographical andGeological Setting
The potters kiln is situated in the Lühlingsbach valley 3km
northeast of Brilon-Alme and 3km west of Bad Wünnen-
berg-Bleiwäsche (Fig.1). Geographically, the site belongs
to the eastern Sauerland region in North Rhine-Westphalia,
Germany. Geologically, the region is part of the Rhenish
Massif (Rheinisches Schiefergebirge), which belongs to
the Rhenohercynian Zone of the Variscan belt in Central
This invited article is part of a special topical issue of the journal
Metallography, Microstructure, and Analysis on Archaeometallurgy.
The issue was organized by Dr. Patricia Carrizo, National
Technological University—Mendoza Regional, and Dr. Omid
Oudbashi, Art University of Isfahan and The Metropolitan Museum
of Art, on behalf of the ASM International Archaeometallurgy
Committee.
* S. Klein
sabine.klein@rub.de
1 Institut für Archäologische Wissenschaften, Ruhr-Universität
Bochum, Am Bergbaumuseum 31, 44791Bochum, Germany
2 Forschungsbereich Archäometallurgie, Deutsches
Bergbau-Museum Bochum, Am Bergbaumuseum 31,
44791Bochum, Germany
3 Competence Center Archaeometry – Baden-Wuerttemberg
(CCA-BW), Universität Tübingen, Wilhelmstraße 56,
72074Tübingen, Germany
4 Forschungslabor der Abt. Forschung, Deutsches
Bergbau-Museum Bochum, Herner Str. 45, 44787Bochum,
Germany
5 Wissenschaftsbereich Georessourcen und Verfahrenstechnik,
Technische Hochschule Georg Agricola, Herner Str. 45,
44787Bochum, Germany
6 Außenstelle Olpe, LWL-Archäologie für Westfalen, In der
Wüste 4, 57462Olpe, Germany
7 Referat Mittelalter und Neuzeitarchäologie,
LWL-Archäologie für Westfalen, An den Speichern 12,
48157Münster, Germany

Metallography, Microstructure, and Analysis
1 3
Europe. This fold-and-thrust belt is composed of Paleozoic
(Ordovician to Carboniferous) sediments and volcanic rocks
which were overprinted by a very low grade metamorphism
[1]. The site is situated in an approximately 17-km-long,
SW–NE striking anticlinal structure, the Brilon anticline.
The core of the anticline is composed of Middle to Upper
Devonian biostromal and intertidal limestones with a thick-
ness of >1250m [2–4].
The carbonatic rocks of the Brilon anticline host a great
number of mineral veins and metasomatic deposits, predom-
inantly bound to NNW–SSE striking normal faults [5, 6].
In addition to barren calcite, barite, and quartz veins, doz-
ens of Pb-Zn-Fe mineralizations are known. The main ore
minerals are galena, calamine, and limonite/goethite. Field
observations show that the mineralizations are undeformed
and therefore of post-Variscan age [6]. K-Ar dating of illites
(< 2mm) related to the calcite veins of the Eichholz mine
near Thülen suggests a mineralization age of ~ 170Ma (Mid-
dle Jurassic) [7], which is in good agreement with other post-
Variscan mineralization ages in other parts of the Rhenish
Massif [8]. Mining took place predominantly in the oxida-
tion zone [5], so that parts of the primary sulfides (galena,
sphalerite/schalenblende, pyrite) are present in weathered
form (cerussite, calamine, limonite/goethite). Galena gener-
ally is silver-poor; Ag measurements of 27 galena samples
from the Brilon mining district reveal low silver contents
of 90ppm at maximum [6, 9]. The silver-poor galena was
an important raw material in the production of lead glazes
for ceramic products and was therefore named “glaze ore”
(“Glasurerz,” “Bleiglasurerz”) [10]. Coarse-grained galena
occurs in calcite, barite, and quartz veins, but up to > 100kg
heavy masses also were found in clays (“Letten”) accom-
panying the veins and in clay fillings of dolines and other
karst sediments ([5], own observations). Galena and clays
can therefore occur side by side in the former Brilon mining
district.
Evidence for galena exploitation occurs already by
Roman time (end of the first century CE) and again, in the
eleventh century CE [11, 12], which was confirmed by a
radiocarbon dating of one charcoal sample [13]. A large
number of pinge fields, tapping and forging slags prove
extensive ore processing of lead. The produced lead was
used for many purposes such as lead anchors, lead pipes,
weights, and other daily use. The deposits, the so-called lead
glaze veins, were excellently suited for use as a glaze com-
ponent for ceramic products. The lead in glazes acts as both
a network former and a network converter, so lead glazes
do not require a complicated recipe to work. The glazing
temperatures can also be kept at a very low level.
Archaeological Setting
The fragments are from an archaeological site in the Lüh-
lingsbachtal, which is located approximately 10km from
Brilon. Archaeological site and excavation are described in
detail by Essling-Wintzer etal. 2016. The Lühlingsbachtal is
surrounded by the mountain range of the Buchholz, a stream
runs through the valley, and the slopes are arboreous. There
is an extensive field of Pingen [14]. Local amateur historians
discovered a vast number of ceramic findings, and likewise,
misfires were identified. These suggested that not only ores
were smelted at the site (as evidenced by the discovery of
slag with adhering furnace walls), but also pottery was pro-
duced. An excavation during autumn/winter 2014 was to
provide clarification about the condition of the soil monu-
ment, but also to localize potential pottery production. Dur-
ing this campaign, remains of a furnace were found. The kiln
dome may already have been dismantled after the last fire
for opening to remove the content and subsequently weath-
ered. The furnace plate, on the other hand, was torn away
by plowing. The lower parts of the furnace, the working pit
and the firing chamber, were deeply carved out of the bed-
rock, which is why they had not been destroyed by plowing
and could be excavated. The kiln was a horizontal cross-
droughted two-chambered (fireplace and firing chamber)
kiln, as supposed from field evidence. The combustion and
firing chambers were separated from each other by a clay
construction to transfer the hot air more homogeneously into
the combustion chamber. The kiln was oriented in the field
Fig. 1 Geographic location of the finding site. In close-up, the geo-
logical setting of the Brilon anticline region is sketched (modified
according to [6]). Brick signature = Upper Carboniferous; Stip-
pled signature = Lower Carboniferous. Locations 1–8: 1 = Quarry
Bleiwäsche; 2 = abandoned Buchholz mine; 3 = Quarry Mad-
feld; 4 = Weiße Kaule; 5 = Nüllstein; 6 = Kirchloh; 7 = Kanzlei;
8 = Schlammkeule

Metallography, Microstructure, and Analysis
1 3
so that natural wind could support the fire. An important
finding in the excavation was a waste dump next to the kiln
with lots of clay fragments. These included rim sherds, body
sherds, bottom sherds from different kinds of ceramics, but
also miniature vessels and some round-bottomed jars and
bowls. The sherds are of different thickness and from oxidic
firing. A large number, especially the miniature vessels and
bowls, have remnants of glazes on the outer and/or the inner
side, which was suspected to be lead glazing. The color of
the glazes varies from light yellowish green to red–brown.
Based on the thin-walled low-fired and unglazed sherds
from round-bottomed jars, which remained in the furnace
from the latest furnace cycle, it can be determined when
the kiln was last in operation. Their typology, especially
the protruding rims with grooves and the rounded rim end,
indicates the late twelfth/early thirteenth century [13]. This
allows the conclusion that as early as the thirteenth century
lead-glazed earthenware was produced in the region around
Brilon-Alme. Ore mining (lead ore, calamine) was active
until the 1880s [5], and calcite deep mining lasted until the
end of the twentieth century.
The Materials
The 13 fragments from the waste dump were provided by
the Landschaftsverband Westfalen-Lippe (LWL). Eight
of them (Figs.2 and 3; Table1) were subject to material
investigation. Four unglazed sherds and a miniature ves-
sel were excluded; the latter because it was a distinctly
different type and pottery and appeared too precious to be
subjected to destructive analysis. The examined fragments
consist of coarsely fired clay and glaze attachments. Three
samples (A45170048_4; _8b; _8c) were archaeologically
identified as crucible rim fragments. One is described
as a ceramic wall fragment (A45170048_8a) and two
(A45170048_11b; _11d) as furnace wall fragments. Two
samples are lumps of undefined shape (A45170048_11e;
_11f), which cannot be assigned to a ceramic typology
or function. It is obvious that they are all clearly differ-
ent from the thin-walled, round-bottomed vessels from
the kiln, and the archaeological address as crucibles or
furnace walls suggests a metallurgical context. The glaze
varies greatly in extent and coloration and is found on both
exterior and interior surfaces. Some are smoothly coated;
others adhere as silvery-gray drips.
For comparison with local ore, a sample of post-Vari-
scan galena (AKZ 4518, 52:007) from a medieval galena
mine [15] in the Buchholz Forest 1.5km southwest of
Bad Wünnenberg-Bleiwäsche (UTM 478,244/5701618),
less than 2km away from the archaeological site, was
analyzed. The archaeological site was recovered by LWL
Archaeology for Westphalia in 2017 from an area that was
not remolded by mining operations.
Fig. 2 Drawings of the glazed objects (by S. Fischer-Lechner)

Metallography, Microstructure, and Analysis
1 3
Fig. 3 Macrophotographs of the glazed objects
Table 1 Ceramic fragments from the waste dump. Inventory numbers and object details
Item number Type Height in mm Width in mm Size in mm Weight in g Temper Glazing Glazing color
A45170048_4 Rim fragment
(crucible) 56 66 19.76 64 Coarse Remains on
surface Olive green
A45170048_8a Ceramic wall frag-
ment 98 69 5.47 51 Coarse Remains on sur-
face and reverse
side
Brownish
A45170048_8b Rim fragment
(crucible) 57 49 13.15 46 Coarse Remains on
surface, reverse
side completely
Olive green
A45170048_8c Rim fragment
(crucible) 106 55 20.4 118 Coarse Remains on
surface Brownish green
A45170048_8d Miniature jar 34 43 25 10 Fine Remains outside
and inside Dark brown
A45170048_11b Rim fragment
(furnace wall) 45 36 8.68 13 Coarse Remains on
surface, reverse
side brown
Olive green
A45170048_11d Rim fragment
(furnace wall) 40 39 13.78 16 Coarse Remains on
surface, reverse
side completely
Olive green
A45170048_11e Lump 68 56 36 111 Coarse Drips Silvery-gray drips
A45170048_11f Lump 40 51 26.41 34 Coarse Drips, metallic
inclosures Silvery-gray drips

Metallography, Microstructure, and Analysis
1 3
Metallurgical Background toResearch
Apart from ceramic glazes in pottery production, coatings
of amorphous silica-rich layers have been observed repeat-
edly in metallurgical contexts. An outstanding example
is known from the copper metallurgy at Ras en-Naqab in
Jordan. Here, white sandstone and dolomitic limestone lin-
ing were used to build up copper smelting furnaces, and
the excavated lining fragments are covered with green, red,
or black glazes [16]. Comparable glazes formed over sand-
stone blocks in smelting furnaces and as glass coatings of
crucibles are reported [16–18]. A special feature, which
does not require silica-rich glazing powder, is quartz
ceramic over which intense blue glazes can be produced
by chemical interaction between the quartz ceramic and
copper pigment or copper vapors [19]. It is also described
that the Romans added litharge, a metallurgical by-product
of lead-silver smelting as a coloring agent for opaque yel-
low and green Roman glasses [20].
All these examples show that glazes occurring do not
necessarily have a deliberate pottery background, but can
also have a metallurgical context. It is obvious that the
fragments coated with lead glazes from Brilon must have a
relationship to the metallurgy of the lead-rich galena since
it was exploited and smelted exactly in the neighborhood.
The archaeological classification as crucibles and the thick
adhesions and drips of glaze on the lumps fit well with this
idea. The following investigations could shed new light on
similarities between glazes from metallurgy and pottery
production.
Experimental Methods andTests
Non‑destructive andMinimally Destructive Testing
EDS–SEM
Scanning electron microscopy was carried out in the labo-
ratories of the Deutsches Bergbau Museum in Bochum. The
instrument used is a Zeiss Supra 40 VP with a field emission
gun. The analyses were performed insitu on the surfaces of
the ceramic fragments. Variable pressure mode was used,
so carbon sputtering was not required. Several particularly
suitable areas were selected for examination on each sample,
i.e., where significant amounts of glaze or thicker drops of
glaze adhered, which were marked prior to facilitating detec-
tion. The magnifications used in the examinations performed
for this work ranged from 24× to 1156× magnification. Sem-
iquantitative elemental analyses at the selected areas were
performed using an energy-dispersive system (EDS).
Destructive Testing
Powder X‑Ray Diffraction (XRD) andMicro‑XRD (µ‑XRD2)
Glaze residue was removed from crucible rim fragment
A45170048/8c with a scalpel, ground to powder with an
agate mortar, and pressed onto a glass slide. The second
sample was one of the lumps (A45170048/11f), from which
the thick silvery-gray adherence was released with forceps
and also ground to powder. XRD phase analysis of the two
samples (A45170048/8c; A45170048/11f) was performed in
the research laboratory of the Deutsches Bergbau-Museum
in Bochum using a PANalytical X’Pert Pro X-ray powder
diffractometer with a Cu x-ray source.
For a more detailed investigation of the microscopi-
cally observed crystals in the glaze of crucible rim frag-
ment A45170048/8c, non-destructive and spatially resolved
x-ray diffraction was performed at the CCA-BW in Tübingen
directly on the exposed sections using a Bruker D8 Dis-
cover-GADDS micro-diffractometer equipped with a Co
x-ray source and a large two-dimensional VÅNTEC-500
detector (μ-XRD2) [21]. The beam diameter of the pri-
mary x-ray beam was approximately 80μm using a 500μm
polycapillary X-ray optic. The PDF-2 database from ICDD
(International Centre of Diffraction Data) was used for phase
identification.
Lead Isotope Analysis
A portion of the galena sample (AKZ4518, 58:007)
and glaze samples from two crucible rim fragments
(A45170048/4 and A45170048/8b) were prepared for lead
isotope analysis. For the two fragments, the material was
obtained first by scraping off glaze residue from the surface
with a scalpel; in addition, the very tightly adhering glaze
was removed more successfully by using adhesive tape in
combination with an excavator. Small sample quantities of
1–10mg were sufficient for lead isotope analysis [22]. In an
ultra-clean laboratory, the samples were dissolved in HF/
HNO3. Lead was separated based on a standardized proto-
col for the column chromatographic process [23]. This way,
the lead was separated from the accompanying elements
and concentrated. The lead solution was finally diluted to
a 2% concentration of HNO3. In the multi-collector mass
spectrometer (Neptune Plus high-resolution MC-ICP-MS,

Metallography, Microstructure, and Analysis
1 3
ThermoFisher Scientific), the prepared lead solution was
then injected in a plasma.
The lead isotopes 204Pb, 206Pb, 207Pb, and 208Pb are sepa-
rated in a magnetic field according to their mass. The advan-
tage of a multi-collector device is that the isotopes of an
element can be detected simultaneously. Tl standard is used
for mass bias correction, and standard reference solution of
NIST Pb 981 as an external standard. From the intensities
obtained, lead isotope ratios are calculated. Lead isotope
analysis is a common tool in archaeometry to discriminate
and hence locate potential ore deposits. The lead isotope
analysis of the fragments and the galena sample can be
compared with lead deposits based on available reference
ore data in the literature and databases [24, 25]. It must be
noted at this point that the ores from which the reference
data have been acquired were newly collected and are not
identical to those actually mined in medieval times. It can
be assumed that surface-near oxide ores were used first and
that the sulfide ores were mined later. As far as it is known,
the lead isotopy is not significantly different for oxidic and
sulfide ores.
Results andDiscussion
Macroscopically, all investigated fragments are red-colored
and were hence fired under oxidizing environment as was
previously proposed [13]. The glaze appears light to darker
olive green to dark brown. The thickness of the glaze is
heterogeneous, and in two examples (A45170048_11e and
_11f), larger drips are attached to the fragments. Under
polarized light microscopy, the substrate is a sub-micro-
scopic clay with subangular quartz grains. The texture
includes aligned shrinking cracks or such surrounding the
quartz grains. The fragments reveal that they were pre-fired
at rather low temperature, as one can observe a reaction zone
between the clay body and the glaze layer. The reaction zone
testifies to the fact that the clay fraction was melted here
and chemically feeds the glaze, as one can see the material
change in the backscattered SEM images, whereas quartz
temper remained unchanged in shape and had not even par-
tially melted (Fig.4). The appearance meets in result of what
also is known as common European medieval technique
[26]: Lead ore or lead oxide was applied to the surface of the
clay substrate, and under eutectic temperature, the glass ore
obtains the required amount of silica from the clay. The Ger-
man term is “Glasurerz-Rezept.” The lead-rich eutectic tem-
perature in the PbO-SiO2 system is at 720°C [27]. Angular
to subangular relics of the ground galena ore in clay, glaze
layer, or interface could be expected when considering this
technique. In the Brilon samples, lead inclusions in the glaze
are only observed as white globular spots in the microscale.
Contrary to what is described for calcareous circumstances
[28], the Brilon glazes are not significantly porous.
The glaze layer of crucible rim fragment A45170048/8c
has an amorphous glassy structure and turned out to con-
sist of a basic colorless glaze, in which a yellow phase had
crystallized. Under the SEM in backscattered mode, differ-
ent gray shades occur due to differences in the lead content
of the glaze. The glaze layers are pervaded by cracks, and
closed globular pores are observable. In one fragment, the
glaze has intruded into the ceramic in molten state. The
interface between the glaze and clay substrate appears as
a reaction zone between both (Fig.4). The glaze is hetero-
geneous in composition as can be seen in the BSE image.
Crystallized components in the amorphous glaze seem
to always occur in chemical exchange with the glaze
matrix: In darker gray areas, dark gray acicular crystals
solidified, sometimes accumulated in sheaves. In lighter
gray areas, white acicular crystals formed and are oriented
along the interface between lighter and darker areas. Tri-
angular crystals form clusters. Around clay fragments in
the glaze layer, skeletal crystals had formed. Clay substrate
and glaze have reacted as can be seen by a flow texture
around the fragment. The different crystals observed are
Fig. 4 Glaze layer and reaction zone between clay and glaze of sam-
ple A45170048_8b. The glaze is heterogeneous in composition and
contains BSE white inclusions of lead. The clay has reacted and
feeds the glaze with its components, while the quartz grains were not
affected by the firing temperature

Metallography, Microstructure, and Analysis
1 3
in total very small (< 100µm) and, respectively, thin and
could not be identified by the microscopical methods.
Greenish-yellow acicular crystals grow from the sur-
face of the colorless glaze in direction of the clay sub-
strate starting to crystallize along the surface of the
glaze and develop toward the ceramic interface (samples
A45170048_8b and A45170048_8c). Along the surface of
the glaze, they form a solid crystal film. The strong ther-
mal gradient between the rapidly cooling surface of the
glaze and the slow-cooling clay substrate is responsible for
the crystal film. The tiny crystals solidify in the surficial
chill zone where the glaze remains as a melt and solidi-
fies in an amorphous state later. Below the chill zone, the
grains develop as columnar grains (Fig.5). If they grow
too large to resist the convection forces of the still molten
glaze, they tear and disperse in the melt. What is notewor-
thy is that the chill zone results in a complete covering of
the colorless glaze surface with a film of yellow crystals,
which optically give the glaze a yellow to greenish color.
A rounded inclusion, around which crystals accumulate,
cannot be clearly identified by the microscopic methods, but
it appears to be a well-rounded fragment of clay. Colorless
skeletal crystals stick out along the surface of the fragment.
The glaze around the crystallized edge of the fragment is
visibly brighter and has a flow texture (Fig.6). It appears
that the surrounding glaze offered components of its chem-
istry to the colorless crystals around the clay fragment. The
crystals are extremely small and thin and hence cannot be
analyzed without a compositional background of the glaze.
However, comparable crystallization phenomena were pre-
viously presented in the literature. Reedy 2016 identified
such needle-like crystals in comparable context as anorthite
when interacting with the glaze. Wollastonite and hercynite
were also mentioned, and cristobalite, the high-temperature
modification of quartz, was described accordingly [29, 30].
By experimental work with a glazing mixture of PbO + SiO2,
Pb-rich feldspar crystals were produced in the diffusion zone
of clay and glaze layer [31], and long firing and slow cooling
resulted in more effective diffusion of elements resulting in
a higher quantity of lead-potassium-rich feldspars. Diffusion
of iron from the clay substrate to the glaze layer was also
described [28]. Additionally, the incorporation of alumina
and potassium was observed in the experiments. With XRD,
we were able to identify only orthoclase, microcline, and
Fig. 5 Cooling history of the yellow crystals in the glaze layer of
sample A45170048_11. Chill zone with tiny crystals (upper left),
below this and in direction to the ceramic (bottom right): columnar
grains
Fig. 6 Clay fragment in the glaze layer of sample A45170048_11.
The glaze has changing chemistry around the clay fragment. Skeletal
crystals form around the fragment, seemingly growing from the sur-
face of the fragment into the still molten glaze Fig. 7 Tandem glaze layer of sample A45170048_8 which is visibly
separated by a film of yellow crystallization (S. Fischer-Lechner)

Metallography, Microstructure, and Analysis
1 3
sanidine in samples A45170048-8 and 11. The richness of
the composition of lead-silica crystallization in the diffusion
zone as described in the literature [31] is not observable in
the Brilon samples. This indicates rather fast cooling condi-
tions so that the reaction partners have not had sufficient
time to form the complex lead-potassium-alumina-rich
phases.
Sample A45170048_8c shows a peculiarity; namely, a
tandem layer of glaze was identified (Figs.5 and 7). Two lay-
ers on top of each other were observed, on each of which the
yellow crystals had formed from the chill zone of the surface
of the glaze toward the ceramic (Fig.7), which indicates fast
cooling conditions of the glaze. This allows no other con-
clusion than the following sequence of solidification: The
first glaze layer was allowed to cool and solidify: yellow
crystals formed on the surface. Then, either intentionally
or by chance, the process was repeated in the same way, so
that the pottery was covered with a second glaze layer, on
the surface of which again tiny yellow crystals were formed.
Scanning electron microscopy confirmed the visually
observed structures and phases (Table2). The amorphous
glaze was analyzed in the different samples. Figure8 visual-
izes the bulk composition and statistics based on the SEM
analyses. The glaze produced on the investigated ceramic
is a silica glass with 4.5–7.4wt.% (first and third quartiles)
alumina as a second component, and only minor amounts
of potassium < 1.9wt.% (third quartile), calcium < 0.7wt.%
(third quartile), magnesium < 0.4wt.% (third quartile), and
sodium < 0.4wt.% (third quartile). Compared to the clay
substrate, the glazes are not consistently enriched with silica
(Fig.9) and therefore do not correspond to the picture given
for intentional glazes produced by applying SiO2 + PbO [32].
The lead addition to the silica glass is also rather random
with 13.1–26.3wt.% (first and third quartile) to 44. 9wt.%
at maximum (Fig.10) and does not meet the transparent
high lead glazes from Europe and the Near East spanning
the period from the third to eighteenth century CE [33].
Iron content ranges between 2.4 and 3.5wt.% (first and third
quartiles), which contributes substantially to the green to
brown color of the glazes.
The gray and skeletal crystals were analyzed, and they
were found to contain less lead than the amorphous glaze.
It remained difficult to identify them, because they are even
too small and thin for the SEM and hence are not really dis-
tinguished significantly from the composition of the amor-
phous glaze. Presumably, the gray crystals are crystallized
lead-silica phases, which grew from the glaze melt, while it
cooled down. Furthermore, the yellow crystals forming on
the surfaces could not be identified by elemental analysis
in the energy-dispersive SEM. The analysis was not con-
clusive, once detecting arsenic and sulfur, but not in other
regions. The post-Variscan galena from Brilon was described
as being nearly arsenic-free (< 10ppm, Atomic Absorption
Spectrometry; Schaeffer 1984). As mentioned earlier, arse-
nic and lead overlap in the energy spectrum. Since lead is
present in high amounts in the samples, arsenic has been
considered a fragment in the spectrum. Because the meas-
urements yielded iron content, the guess was hematite. How-
ever, the crystal shape of the observed yellow crystals is
contradictory to the crystallography of trigonal hematite.
For this reason, a powder XRD (XRPD) was performed
on the powders of glazes adhering to two fragments. The
thermal phase (trans-)formation of glazes in the PbS-SiO2
system was investigated previously by high-temperature
resolved XRD and the phase diagram was investigated
[34]. In the glaze layer of fragment A45170048/8b, the
crystallized components quartz, orthoclase, hematite and
lead (Pb) were identified; in the glaze layer of fragment
A45170048/11f, sanidine and lead (Pb) were identified.
No evidence was found for phase identification of the yel-
low acicular crystals. Therefore, µ-XRD analysis was per-
formed at the CCA-BW in Tübingen to identify the yel-
low crystals directly in noncovered cross-sections. In this
way, melanotekite, a synthetic orthorhombic sorosilicate
(Pb2Fe23+(Si2O7)O2) could be identified (Fig.11). Mel-
anotekite was reported earlier in lead glaze-related publica-
tions, and its phase relation to hematite and consequences for
the reconstruction of melting temperatures were discussed
[32, 35]. It can result in yellow to brown decorations, e.g., of
seventeenth-/nineteenth-century CE ceramic lead glaze [30].
Reviewing the powder diffractograms for this phase finally
delivered the complete picture of crystallized phases as pre-
sent in the glaze layers (Table3). Hematite is in no case
co-existent with melanotekite here. Since melanotekite dis-
solves completely at firing temperatures above 920°C (fol-
lowing Di Febo etal.’s arguments [35]), from which during
cooling it can form the observed skeletal yellow crystals, the
presence of the phase in absence of hematite indicates rather
high melting temperatures to produce the glazes adhering on
the lumps from Brilon.
To position the glaze layers into the metallurgical con-
text of the region, the galena sample and two samples of
the glaze have been analyzed for lead isotope composition
(Table4). The lead isotope signature of the glaze is domi-
nated by the lead component, so that the glazes could be
compared with the lead ores of the region. Reference data
of lead ores from the Brilon region are provided in the dis-
sertation of M. Bode [9]. While the two glaze samples show

Metallography, Microstructure, and Analysis
1 3
Table 2 EDS–SEM analysis of the glaze layer, crystallized phases and ceramic body in the analyzed samples
Object Component O Na Mg Al Si P S K Ca Ti Fe Cu As Pb
weight percentage, normalized to 100%
Glaze layer
A45170048/11b Amorphous glass 46.6 0.0 0.7 5.2 31.0 0.0 0.0 1.0 1.1 0.0 3.4 0.0 0.0 11.0
A45170048/11b Amorphous glass 47.5 0.0 0.9 5.8 27.5 0.0 0.0 1.1 1.3 0.0 3.7 0.0 0.0 12.2
A45170048/11b Amorphous glass 47.4 0.0 0.8 6.1 26.7 0.0 0.0 1.3 0.9 0.0 3.1 1.5 0.1 12.0
A45170048/11b Amorphous glass 33.9 0.0 0.5 4.7 26.1 0.0 0.0 0.9 0.7 0.0 3.1 1.5 12.4 16.2
A45170048/11b Amorphous glass 37.3 0.0 0.5 4.5 24.3 0.0 0.0 0.7 0.7 0.4 2.3 1.0 9.9 18.5
A45170048/11b Amorphous glass 38.8 0.0 0.6 4.8 19.7 0.0 0.0 0.8 0.5 0.0 3.0 0.0 0.0 31.8
A45170048/11b Amorphous glass 33.6 0.4 0.3 4.6 24.6 0.0 0.0 1.0 0.6 0.0 2.4 1.7 10.5 20.3
A45170048/11b Amorphous glass 34.1 0.0 0.4 5.5 26.8 0.0 0.0 1.0 0.0 0.4 2.0 1.5 15.5 13.1
A45170048/11b Amorphous glass 34.2 0.0 0.4 4.3 22.2 0.0 0.0 0.8 0.6 0.0 2.5 1.9 0.0 33.0
A45170048/11b Amorphous glass 39.6 0.0 0.0 4.1 25.9 0.0 0.0 1.2 0.8 0.0 0.0 2.4 0.2 25.6
A45170048/11b Amorphous glass 38.2 0.0 0.0 4.5 25.6 0.0 0.0 1.1 0.4 0.0 3.0 2.0 0.1 25.1
A45170048/11b Amorphous glass 39.1 0.4 0.0 4.9 27.9 0.0 0.0 1.2 0.7 0.0 3.8 1.9 0.7 19.4
A45170048/11d Amorphous glass 39.1 0.0 0.0 7.4 27.9 0.0 0.0 2.2 0.0 0.0 3.5 1.5 0.5 17.9
A45170048/11b Transition zone 47.0 0.4 0.5 9.8 27.9 0.0 0.0 5.4 0.0 0.0 2.2 0.0 0.0 6.8
A45170048/11d Amorphous glass 43.5 0.2 0.0 7.7 31.6 0.0 0.0 3.5 0.6 0.0 3.6 0.0 0.3 9.0
A45170048/11d Amorphous glass 41.9 0.4 0.0 7.4 29.9 0.0 0.0 3.4 0.0 0.0 2.9 0.0 0.5 13.6
A45170048/11d Amorphous glass 37.1 0.0 0.0 9.4 23.7 0.0 0.0 1.8 0.0 0.0 2.7 0.0 0.5 24.8
A45170048/11d Amorphous glass 33.9 0.0 0.5 12.5 25.5 0.0 0.0 1.3 0.0 0.0 3.3 0.0 9.3 13.8
A45170048/11d Amorphous glass 29.4 0.0 0.0 12.5 23.3 0.0 0.0 1.1 0.0 0.5 2.4 0.0 14.4 16.5
A45170048/11e Amorphous glass 33.6 0.0 0.0 5.3 13.8 0.0 0.0 1.9 0.0 0.0 3.1 0.0 0.0 42.4
A45170048/11e Amorphous glass 37.3 0.0 0.4 4.5 21.9 0.8 0.0 1.3 1.4 0.0 3.8 1.8 0.2 26.5
A45170048/11e Amorphous glass 38.9 0.6 0.6 4.4 20.5 0.0 0.0 1.4 0.6 0.4 2.6 1.9 0.0 28.0
A45170048/11f Amorphous glass 40.3 0.0 0.6 4.8 26.1 0.0 0.0 1.4 0.7 0.7 3.0 0.0 0.0 22.5
A45170048/11f Amorphous glass 45.6 0.0 0.7 5.8 31.1 0.0 0.0 1.7 1.0 0.0 3.8 0.0 0.0 10.4
A45170048/11f Amorphous glass 49.1 0.5 0.0 6.7 28.5 0.0 0.0 2.2 1.1 0.5 3.1 0.0 0.5 7.9
A45170048/11f Amorphous glass 44.6 0.4 0.0 5.3 24.4 0.0 0.0 1.5 1.3 0.0 4.0 0.0 0.0 18.5
A45170048/11f Amorphous glass 46.5 0.1 0.0 6.0 32.3 0.0 0.0 1.3 1.2 0.0 3.8 0.0 0.4 8.4
A45170048/11f Amorphous glass 29.3 0.0 0.6 3.3 17.6 0.0 0.0 0.8 0.8 0.0 2.7 0.0 0.0 44.9
A45170048/11f Clay fragment bright area 40.3 0.0 0.8 4.4 25.6 0.0 0.0 1.1 0.9 0.6 2.9 0.0 0.0 23.4
A45170048/11f Clay fragment bright area 46.1 0.0 0.7 5.6 29.6 0.0 0.0 1.5 0.9 0.7 4.3 0.0 0.1 10.4
A45170048/11f Clay fragment dark area 46.7 1.0 0.0 11.3 27.8 0.0 0.0 6.7 0.0 0.0 1.6 0.0 0.0 4.9
A45170048/11f Clay fragment dark area 43.9 0.7 0.6 13.6 24.4 0.0 0.0 3.7 0.7 0.0 7.1 0.0 0.0 5.4
A45170048/11f Clay fragment dark area 46.1 0.9 0.0 10.0 28.1 0.0 0.0 8.3 0.0 0.0 1.3 0.0 0.0 5.5
A45170048/11f Skeleton crystal 45.3 0.6 0.2 8.8 28.2 0.0 0.0 8.5 0.0 0.0 1.4 0.0 0.0 6.9
A45170048/4 Acicular crystal 37.0 0.0 0.5 4.7 15.6 0.0 0.0 0.6 0.0 1.3 13.3 0.0 0.0 26.9
A45170048/4 Amorphous glass 37.2 0.2 0.3 5.6 18.4 0.0 0.0 0.7 0.0 0.6 3.5 0.0 0.0 33.3
A45170048/4 Amorphous glass 37.0 0.0 0.4 5.7 20.9 0.0 0.0 0.7 0.0 0.0 4.3 0.0 0.0 30.9
A45170048/8b Amorphous glass 34.0 0.0 0.0 3.5 20.8 0.0 0.0 0.7 0.0 0.4 1.8 0.0 0.0 38.8
A45170048/8b Amorphous glass 38.1 0.0 0.4 4.6 25.8 0.0 0.0 0.7 0.0 0.0 1.2 0.0 0.0 29.3
A45170048/8b Amorphous glass 9.2 0.0 0.0 8.3 49.2 0.0 0.0 0.0 0.0 0.0 4.6 0.0 0.5 28.2
A45170048/8b Amorphous glass 41.7 0.4 0.0 4.0 25.4 0.0 0.0 1.1 0.0 0.4 2.5 0.0 12.4 12.1
A45170048/8b Amorphous glass 41.3 0.4 0.0 3.6 23.4 0.0 0.0 1.2 0.0 0.0 1.5 0.0 0.2 28.3
A45170048/8b Amorphous glass 44.4 0.6 0.0 4.0 27.1 0.0 0.0 1.2 0.0 0.0 3.4 0.0 0.6 18.7
A45170048/8b Amorphous glass 46.2 0.4 0.0 4.0 27.5 0.0 0.0 1.4 0.5 0.5 2.8 0.0 0.3 16.5
A45170048/8b Amorphous glass 47.8 0.7 0.0 4.2 29.1 0.0 0.0 1.4 0.0 0.0 2.9 0.0 0.5 13.3
A45170048/8b Antimony triangular pyramid 45.8 0.0 0.0 3.8 14.2 0.0 0.0 1.0 0.0 3.1 7.9 0.0 0.0 24.1
A45170048/8b Transition zone 45.9 0.5 0.4 9.7 27.9 0.0 0.0 4.3 0.0 0.0 1.9 0.0 0.0 9.4
A45170048/8b Transition zone 47.9 0.6 0.2 10.1 28.4 0.0 0.0 4.0 0.0 0.0 1.7 0.0 0.0 7.2

Metallography, Microstructure, and Analysis
1 3
Table 2 (continued)
Object Component O Na Mg Al Si P S K Ca Ti Fe Cu As Pb
weight percentage, normalized to 100%
A45170048/8c Acicular crystal 33.9 3.1 0.0 0.0 15.9 0.0 0.0 0.0 0.0 1.1 17.6 0.0 0.0 28.5
A45170048/8c Acicular crystal 36.7 0.0 0.6 7.1 21.7 0.0 0.0 0.0 0.0 0.0 19.4 0.0 0.0 14.6
A45170048/8c Acicular crystal 37.2 0.0 0.0 6.5 20.1 0.0 0.0 0.0 0.0 1.1 18.6 0.0 1.0 15.4
A45170048/8c Acicular yellow crystal 47.5 0.0 0.8 3.2 20.5 0.0 0.0 0.8 0.0 1.0 16.7 0.0 0.0 9.5
A45170048/8c Acicular yellow crystal 38.9 0.0 0.2 3.1 18.8 0.0 0.0 0.0 0.0 1.0 22.7 0.0 0.0 15.3
A45170048/8c Acicular yellow crystal 34.1 0.0 0.3 2.4 15.0 0.0 0.0 0.0 0.0 0.8 18.8 0.0 0.0 28.6
A45170048/8c Acicular yellow crystal 43.7 0.0 0.3 3.7 20.4 0.0 0.0 0.8 0.0 0.7 22.7 0.0 0.0 7.7
A45170048/8c Acicular yellow crystal 41.5 0.0 0.0 3.5 20.6 0.0 0.0 0.0 0.0 0.0 23.8 0.2 0.0 10.4
A45170048/8c Amorphous glass 49.7 0.0 0.7 6.1 29.3 0.0 0.0 0.7 1.7 0.0 3.7 0.0 0.2 7.9
A45170048/8c Amorphous glass 31.4 0.0 36.9 3.8 18.8 0.0 0.0 0.6 0.9 0.0 1.9 0.0 0.1 5.7
A45170048/8c Amorphous glass 43.4 0.0 0.5 6.5 27.1 0.0 0.0 0.9 0.0 0.0 2.9 0.0 0.0 18.6
A45170048/8c Amorphous glass 37.8 0.0 0.4 4.9 22.5 0.0 0.0 0.6 0.0 0.0 2.3 0.0 0.0 31.5
A45170048/8c Amorphous glass 46.1 0.0 0.5 7.1 26.0 0.0 0.0 0.8 0.6 0.0 3.9 0.0 0.0 15.0
A45170048/8c Transition zone 48.4 0.7 0.4 10.8 27.3 0.0 0.0 4.4 0.0 0.0 1.7 0.0 0.0 6.3
A45170048/8c Transition zone 42.4 0.0 0.6 5.2 26.5 0.0 0.0 0.8 0.9 0.0 3.2 0.0 0.0 20.3
A45170048/8c Transition zone 48.0 0.8 0.0 13.1 26.8 0.0 0.0 4.4 0.0 0.0 1.1 0.0 0.0 5.8
A45170048/8d Acicular crystal 48.9 0.4 0.0 7.1 30.4 0.0 0.0 4.4 0.0 0.0 1.2 0.0 0.0 7.5
A45170048/8d Acicular crystal 44.7 0.5 0.0 11.3 29.2 0.0 0.0 7.9 0.0 0.0 1.3 0.0 2.0 3.0
A45170048/8d Acicular crystal 48.4 0.0 0.3 8.0 31.5 0.0 0.0 5.2 0.0 0.0 1.5 0.0 0.0 5.1
A45170048/8d Acicular crystal 48.2 0.4 0.0 8.7 31.1 0.0 0.0 6.5 0.0 0.0 1.3 0.0 0.4 3.5
A45170048/8d Acicular crystal 45.6 0.7 0.4 11.1 23.4 0.3 0.0 6.0 0.0 0.0 2.7 0.0 0.0 9.8
A45170048/8d Amorphous glass 47.3 0.2 0.0 8.1 28.4 0.0 0.0 4.2 0.0 0.0 0.8 0.0 0.0 11.1
A45170048/8d Amorphous glass 46.4 0.4 0.0 9.4 30.0 0.0 0.0 3.8 0.0 0.0 1.9 0.0 0.1 8.0
A45170048/8d Amorphous glass 43.1 0.0 0.0 10.0 30.0 0.0 0.0 2.4 0.6 0.0 3.3 0.0 0.6 10.0
A45170048/8d Amorphous glass 47.7 0.0 0.0 9.0 31.6 0.0 0.0 4.1 0.0 0.0 2.1 0.0 0.2 5.3
AKZ4518 Galena 0.0 0.0 0.0 0.0 0.0 0.0 38.1 0.0 0.0 0.0 0.0 0.0 0.0 61.9
AKZ4518 Galena 0.0 0.0 0.0 0.0 0.0 0.0 35.8 0.0 0.0 0.0 0.0 0.0 0.0 64.2
AKZ4518 Galena 29.9 0.0 0.0 0.0 0.0 0.0 25.2 0.0 0.0 0.0 0.0 0.0 0.0 44.8
AKZ4518 Galena 34.3 0.0 0.0 0.3 0.0 0.0 25.0 0.0 0.0 0.0 0.0 0.0 0.0 40.4
AKZ4518 Galena 0.0 0.0 0.0 0.4 0.0 0.0 35.2 0.0 0.0 0.0 0.0 0.0 0.0 64.4
Clay body
A45170048/4 46.0 0.2 0.7 14.6 22.8 0.9 0.9 3.4 0.0 1.0 9.6 0.0 0.0 0.0
A45170048/4 42.8 0.0 0.7 16.6 22.7 1.3 2.0 4.1 0.0 0.4 9.5 0.0 0.0 0.0
A45170048/8d Small area surrounded by glazing 50.4 0.2 1.2 21.0 16.9 0.0 0.0 2.0 0.5 0.5 4.3 0.0 0.0 2.9
A45170048/11b 67.4 0.0 1.0 4.9 10.1 0.0 0.0 2.9 0.0 0.0 13.7 0.0 0.0 0.0
A45170048/11d Close to glazing 57.9 0.0 0.2 1.9 35.6 0.0 0.1 0.5 0.0 0.4 2.0 0.0 0.0 1.4
A45170048/11d Close to glazing 46.8 0.0 0.0 9.2 20.0 4.6 0.0 0.8 0.5 0.9 14.6 0.0 2.7 0.0
A45170048/11d Small area surrounded by glazing 49.5 0.3 0.0 13.0 19.0 1.7 0.0 2.3 3.6 0.3 8.5 0.0 1.7 0.0
A45170048/11e 52.4 0.0 0.4 4.2 39.9 0.0 0.6 0.6 0.0 0.0 2.0 0.0 0.0 0.0
A45170048/11e 57.5 0.3 0.5 6.0 32.7 0.0 0.0 1.0 0.0 0.0 1.6 0.0 0.0 0.4
A45170048/11f 51.3 0.9 0.6 11.0 26.4 0.6 0.8 3.9 0.0 0.5 4.1 0.0 0.0 0.0
A45170048/11f Small area surrounded by glazing 52.6 0.4 0.0 11.7 25.1 0.3 0.0 2.7 0.6 0.4 4.0 0.0 1.5 0.7

Metallography, Microstructure, and Analysis
1 3
an identical Pb isotope signature within the error limits, the
galena sample contains higher radiogenic lead (Fig.12). The
galena sample and the glazes fit well into the overall picture
of the Brilon anticline. With a closer look into the reference
data, however, two isotope fields can be developed which
distinguish the eastern and the western part of the anticline
(Fig.12). Higher radiogenic lead represents the eastern part
(Alme, Bleiwäsche, Madfeld, Messinghausen, Rösenbeck),
and lower radiogenic lead characterizes the western part
(Brilon and surroundings). The examined galena sample
matches a high medieval lead mine in the Buchholz Forest
in the eastern part. According to finds in the surrounding
area, it can be dated to the tenth–eleventh century, thus even
slightly older than the excavated pottery kiln. As expected,
the analyzed galena sample perfectly matches the ore refer-
ence data from the eastern part of the Brilon anticline. The
glazed fragments originating from the Lühlingsbach valley in
the eastern part were found in close proximity (less than 2km
away) to the site of the galena sample. Surprisingly, their lead
isotope signature is clearly different and rather fits the refer-
ence data of the western part. The best match is actually with
samples from Kirchloh hill 3km southeast of Brilon. It must
Fig. 8 Box–Whisker plot for
the glaze composition. The
glaze composition follows a
recipe of an alumina-silica glass
with 4.3–7.5wt. Al (values in
the box = quartiles 1–3) and
variable and heterogeneous
lead content between 9.2 and
22.2wt.% Pb (values in the
box = quartiles 1–3)
Fig. 9 Comparison of SiO2 concentration in weight percentage in
glaze layer and ceramic body. SiO2 in the glaze layer is elevated, but
rather random
Fig. 10 Ternary diagram SiO2-Al2O3-PbO of analyzed glaze compo-
sition. Lead content is rather random

Metallography, Microstructure, and Analysis
1 3
be emphasized here, however, that [9] reference data were
not compiled with an eye to the fact that the mines were also
operated during the period in question. Further investigation
in the former Brilon mining district is needed to clarify this.
Conclusions
Glazes represent the earliest examples of the production of
glass. Observations related to pyrometallurgical processes
have shown that glazes can be produced even unintentionally
in the smelting furnace. The site of this study is a further
example of a strong relationship between metallurgy and
glaze production. The region is very rich in lead ore. There
is a large number of pits in the area, and metallurgical activ-
ity in the region is evident. Pottery production took place
and has been evidenced by the excavation of a pottery kiln.
Inside the kiln, the latest furnace journey has been pre-
served. The kiln was loaded with unglazed pottery. Remains
which would point to glazing activities such as crushed lead
ore, litharge, quartz, crucibles, grinding tools, or other pig-
ments were not found. The investigated fragments, which
are thick-walled, coarse-grained fragments of crucibles and
furnace walls, were found in a nearby waste dump together
with finely produced and glazed pottery products. Archaeo-
logical evidence hence suggests that the dump was at least
partially filled with metallurgical waste from the pits and not
solely with glazed pottery. It remains unproven whether the
glaze production took place on-site or remotely.
There are many requirements such as chemistry, com-
ponents, or temperatures for the successful production of
pottery glazes. As archaeological examples demonstrate,
the metallurgical context fulfills the same physicochemi-
cal reactions then often described as slagging or vitrifica-
tion: a random silica melt from silica-rich clay enriched
with the endemic metal (e.g., Cu, Fe, Pb): Due to the high
Fig. 11 Image of the measurement location (white ellipse) of the
µ-XRD2 measurement in an area with yellow acicular crystals in the
glaze (left), detector images of the measurement with single-crystal
spots (right) and resulting diffractogram with reference patterns of
melanotektite from the PDF-2 database (bottom) which is in good
accordance with the measured pattern. It is important to note that
the measured intensities are strongly influenced by the single-crystal
intensities which are visible in the detector images. Therefore, they
will not necessarily correlate with the theoretical intensities from
the database. The hump in the diffractogram results from the amor-
phous matrix (glass) of the glaze. Measurement time for each detector
image was 10min. Sample A45170048_8
Table 3 Phases identified by XRPD and µ-XRD2
Sample nb
A45170048_8c A45170048_11f
SiO2, quartz low x
Pb2Fe2(Si2O7)O2, syn. mel-
anotekite x
Al1K1O8Si3, microcline x
KAlSi3O8, sanidine x
Pb1, lead x x
Fe2O3, hematite x
Al1K1O8Si3, orthoclase x

Metallography, Microstructure, and Analysis
1 3
temperatures in pyrometallurgical furnaces, the lining,
technical ceramic, or tuyère tips can be partially melted.
The color spectrum is also equally attainable, so that red,
green, yellow, brown, or black glazes can be formed due
to metal vapors. Neo-crystallized phases (feldspars, SiO2
modifications [16]) also form similarly during the cooling
processes. The glassy layers found on the investigated frag-
ments were identified as amorphous Al-Si-Pb glass with low
concentrations of Na, Ca, K, Mg, and K. They are of a fairly
heterogeneous yellowish-green to brown color. The silica
and lead concentrations are quite variable and apparently
do not follow a consistent mixture. The pottery was not well
prepared, as one would expect a smoothing of the surface
to produce high quality and glossy glaze on pottery (e.g., in
Renaissance pottery [36]). In some cases, glassy drips can be
observed, showing that the glaze was quite viscous at times.
The glaze exhibits numerous cracks, which may indicate
differential shrinkage relative to the clay substrate. It is to be
expected that the cracking would have been avoided in delib-
erate production. The presence of identified melanotekite
and its specific behavior in the melt is indicative of fairly
high furnace temperatures and other lead-silica phases usu-
ally observed from neo-crystallization in the reaction zone
between the clay body and glaze are absent. The colora-
tion is not homogeneous throughout the glaze layer, as it
is expected if ferrous glazes overlay the original clay color.
Rather, when the yellow idiomorphic melanotekite crystals
have formed they are concentrated in the chill zone of the
glaze and are not distributed throughout. This results in a
thin, yellow-to-green film and makes the glaze, which is
colorless in itself, appear yellow to green when observed
by the naked eye. The tandem layer, as observed on one of
the samples and never before, does not meet a professional
glazing process. The molten mass seems to have overflowed
several times rather accidentally.
To summarize, the substantial chemical reactions and
occurring phases observed here were previously character-
ized in the context of lead glazing techniques. However, they
are also consistent with what is known in a metallurgical and
hence non-intentional context. The use of glazed products
in the region is supported by the finds in the excavation,
but the lack of evidence for glaze production in the imme-
diate vicinity leaves the question open of whether or not
pottery activities included glazing on site. It is evident that
pottery production and metallurgical activities were closely
related in the region. Lead isotope analysis has shown that
the fact that the ore is available right on the doorstep does
not mean that it was used exclusively. Apparently, lead ore
was collected and used throughout the region, regardless
of whether it came from the western or eastern part of the
Brilon anticline.
Table 4 Lead isotope results of the lead glazes and the galena sample
The NIST SRM 981 standard reference material was measured as unknown sample for internal monitoring
Sample nb 206Pb/204Pb 2SD 2SE 207Pb/204Pb 2SD 2SE 208Pb/204Pb 2SD 2SE 207Pb/206Pb 2SD 2SE 208Pb/206Pb 2SD 2SE
AKZ
4518,58:007
Galena 18.4500 0.0027 0.0004 15.6187 0.0033 0.0005 38.4062 0.0085 0.0014 0.8466 0.0001 0.0000 2.0815 0.0002 0.0000
A 4517_0048/8b Glaze 18.3450 0.0026 0.0004 15.6111 0.0029 0.0005 38.2752 0.0072 0.0012 0.8510 0.0001 0.0000 2.0863 0.0001 0.0000
A 4517_0048/4 Glaze 18.3464 0.0027 0.0004 15.6110 0.0026 0.0004 38.2761 0.0061 0.0010 0.8510 0.0000 0.0000 2.0862 0.0001 0.0000
Monitoring 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb 207Pb/206Pb 208Pb/206Pb
NIST SRM 981,
n = 7 (2σ)
16.9307 (± 6) 15.4843 (± 6) 36.6752 (± 16) 0.914567 (± 10) 2.16619 (± 4)
Samples normal-
ized to
16.9306 15.4834 36.6749 0.9146 2.1661

Metallography, Microstructure, and Analysis
1 3
Acknowledgements We are grateful to have received the fragments
for analysis by the LWL—Landschaftsverband Westfalen-Lippe. The
elemental and isotope analyses were run in the research laboratory
of the Deutsches Bergbau-Museum Bochum. Our thank goes to Dr.
Moritz Jansen for the lead isotope analyses, Sandra Kruse genannt
Lüttgen for the thin section preparation, and the technical staff of the
laboratory for much help. At the LWL, we would like to thank Maja
Thede for the geographic part of the map and Hannah Zietsch from
the Deutsches Bergbau-Museum/Archaeometallurgy for the geological
redrawing. At the Competence Center Archaeometry—Baden-Wuert-
temberg (CCA-BW), Beatrice Boese is especially thanked for running
the µ-XRD2 measurements. We would like to thank Nadine Svane und
Jana Klepacova for English proofreading. We acknowledge the helpful
comments of the anonymous reviewers and the help of the editor, based
on which we were able to improve our final manuscript.
Fig. 12 Lead isotope diagrams
comparing the own samples
(glazes, galena sample from
Buchholz) and 51 reference data
for the Brilon anticline from the
literature [9]

Metallography, Microstructure, and Analysis
1 3
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