Feature
Archaeotechnology
Ancient Iron and Bronze Pieces from
La Tejada: Characterization Studies
J.M. Gómez de Salazar, M.I. Barrena, and A. Soria
This article describes the microstructural characterization of ancient iron
and bronze found in the archaeological
site of La Tejada (Palencia, Spain). This
work offers insight into the manufacturing and technological knowledge of
Roman society, which would be of
interest for several branches of science
including metallurgy, archaeology, and
chemistry.
INTRODUCTION
The abundance of raw materials
present in the Iberian Peninsula enabled
civilizations throughout the region to
flourish.1 One example is Palencia,
a province in the northwest of Spain
where numerous villages2 and archaeological sites from different eras were
discovered.3 Some of these sites were
Figure 1. A map of La Tejada.
villages and others were thermal baths.
La Tejada, situated on the bank of the
Cueza River and dated in the second
century A.D, is an example of a thermal
bath (Figure 1).4
The thermal bath consisted of three
buildings made of recycled construction
materials. The pillars that supported the
floor (Figure 2) allowed the circulation
of hot air from a furnace to the different
buildings.4 The mosaics (Figure 3) show
the archaeological and artistic richness
of the Roman society. The studies
of artifacts found in La Tejada, an
iron nail and some bronze rods, in
particular (Figure 4), focused on
their microstructural and mechanical
characterization.
The metallographic characterization
was performed using optical microscopy,
scanning-electron microscopy (SEM),
x-ray diffraction (XRD), and hardness
testing. This characterization required
consolidation (by immersing the pieces
in methacrylate solution) to prevent the
losses of oxides and patinas. Moreover,
an etching reactive was used to reveal
the microstructure: Nital (a solution
of HNO 3 in ethanol) for the iron
microstructure and an acid solution
of FeCl3 in ethanol for the bronze
microstructure.5 Oxides and slags were
not electric conductors, so SEM required
a previous sputtering process.
RESULTS AND DISCUSSION
XRD Analysis
Figure 2. A floor supported by pillars.
Figure 3. Mosaics with geometrical forms.
An XRD analysis was carried out
on the surface of the iron nail and
Over the last 40 years, there has been a discernible increase in the number of scholars who have focused their research on early industrial
organizations, a field of study that has come to be known as Archaeotechnology. Archaeologists have conducted fieldwork geared to the study
of ancient technologies in a cultural context and have drawn on the laboratory analyses developed by materials scientists as one portion of their
interpretive program. Papers for this department are solicited and/or reviewed by Michael Notis, a professor and director of the Archaeometallurgy
Laboratory (www.Lehigh.edu/~inarcmet) at Lehigh University.
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JOM • June 2004
the bronze rods. The analysis of the
lands that easily fell apart from the
nail showed the presence of quartz
(SiO2), calcite (CaCO3), and akageneite
(FeOOH) compounds (Table I).
The XRD analysis of the lands that
fell apart from the bronze rods showed
the presence of quartz (SiO2) and cuprite
(Cu2O) compounds (Table II).
Powder diffraction lines identification
show that all these pieces were buried in
a quartzite soil. Cuprite and akagenite
compounds were corrosion products of
these samples.
Optical Microscopy
Optical microscopy images of the
nail show a hypoeutectoid steel in the
external head zone, with a microstructure
consisting of ferrite matrix with pearlite
precipitated in the grain boundary
(Figure 5). In internal zones, the
micrographs show a microstructure with
ferrite and pearlite phases. This zone
presents less pearlite content due to
the decrease of carbon percent (Figure
6). The optical microscopy shows an
α-bronze microstructure in the rods
(Figure 7). This microstructure presents
grains with different sizes. The size of
the grain decreases near the external
zone because of the deformation effect
(cold deformation).
Scanning Electron Microscopy
The SEM study found that the iron
consisted of pearlite and ferrite, where
the ferrite phase presents an acicular
morphology (Widmanstätten) (Figure
8). The rods were manufactured with
7 wt.% tin (Table III), leading to an
α-bronze microstructure that has some
twins (Figure 9). An interesting fact was
observed in the internal zones, where
two different types of slags were found
(Figure 10). The difference between the
slags was their chemical composition
(Table IV)—dark slag (Figure 11)
contained more copper than bright slag,
which had more tin (Figure 12).
a
2 cm
Figure 4. The La Tejada artifacts: (a) a
bronze rod and (b) an iron nail.
b
1 cm
Table I. Powder Diffraction File Identification (Surface of the Nail)
No.
2θ
d (Å)
Rel. I (%)
Mineral
ASTM No.
h
k
l
1
2
3
4
5
6
7
8
9
10
11
12
13
20.98
26.82
29.54
35.06
36.74
39.66
40.50
42.62
50.30
55.06
60.10
67.94
68.34
4.234
3.324
3.024
2.559
2.446
2.273
2.227
2.121
1.814
1.668
1.540
1.380
1.373
19.6
100
15.8
7.2
12.4
10.7
21.9
7.9
15.8
9.9
13.4
7.9
10.6
SiO2
FeOOH
CaCO3
FeOOH
SiO2
CaCO3
SiO2
SiO2
SiO2
SiO2
SiO2
SiO2
SiO2
33-1161
34-1266
72-1650
34-1266
33-1161
72-1650
33-1161
33-1161
33-1161
33-1161
33-1161
33-1161
33-1161
1
3
1
2
1
1
0
2
1
2
2
2
2
0
1
0
1
1
1
1
0
1
0
1
1
0
0
0
4
1
0
3
2
0
2
2
1
2
3
Table II. Powder Diffraction File Identification (Surface of the Rod)
No.
1
2
3
4
5
6
7
8
9
2θ
d (Å)
Rel. I (%)
Mineral
ASTM No.
h
k
l
20.86
26.62
29.54
36.42
39.82
42.34
42.78
49.78
61.38
4.258
3.349
3.024
2.467
2.264
2.135
2.114
1.832
1.510
18.82
25
23.3
100
26.1
41.8
47.2
27.2
42.9
SiO2
SiO2
Cu2O
Cu2O
SiO2
Cu2O
SiO2
SiO2
Cu2O
33-1161
33-1161
78-2076
78-2076
33-1161
78-2076
33-1161
33-1161
78-2076
1
1
1
1
1
2
2
1
2
0
0
1
1
0
0
0
1
2
0
1
0
1
2
0
1
2
0
50 µm
50 µm
Figure 5. An optical micrograph of external
head zones of the nail.
Figure 6. An optical micrograph of internal
zones of the nail.
Hardness Test
The rods were tested using Vickers
hardness. The Vickers hardness is
homogeneous along all pieces with
values in an interval of 115 ± 10 HV.
A hardness test was carried out on the
nail’s head zone and on a longitudinal
section. In the head zone, the hardness
2004 June • JOM
Table III. Chemical Piece Composition
Element
Table IV. Slags Chemical Composition
Wt.%
Element
Si
Fe
Cu
Sn
0.72
0.20
92.04
7.05
O
Si
Cu
Sn
Dark Slag
(wt.%)
Bright Slag
(wt.%)
11.64
2.25
82.09
4.03
15.41
0.84
69.51
14.24
15
increases from the external zones (100
HV) to the central zones (220 HV)
due to deformation hardening and the
subsequent decrease in carbon content
on this forging. In the longitudinal
section, the medium hardness value was
190 ± 30 HV, though the hardness values
decrease near the tip zone.
CONCLUSIONS
100 µm
60 µm
Figure 7. An optical micrograph of αbronze.
Figure 8. A scanning electron microscopy
image of the nail. Ferrite presents an
acicular morphology.
Based on characterization results,
one can conclude that Roman society
in Palencia knew how to forge iron and
bronze, and understood the hardness
processes that took place during cold
work.
References
100 µm
100 µm
Figure 9. A scanning electron microscopy
image of α-bronze (7% Sn).
Figure 10. Elongated slags in the bronze
matrix.
1. R. Martín Valls, Historia de Palencia I. Edades
Antigua y Media (Palencia, Spain: Excma. Diputación
Provincial Palencia, 1984), pp. 15–53.
2. J.M. Gómez de Salazar and A. Soria, “Characterizing
Ancient Iron Pieces from La Olmeda,” JOM, 52 (12)
(2000), pp. 15–17.
3. Montenegro Duque, Historia de Palencia I. Edades
Antigua y Media (Palencia, Spain: Excma. Diputación
Provincial Palencia, 1984), pp. 54–62.
4. M.A. García Guinea, Guía de la villa romana de
Quintanilla de la Cueza (Palencia) (Palencia, Spain:
Diputación de Palencia, 1990).
5. F.A. Calvo, Metalografía práctica (Madrid, Spain:
Alhambra, 1971).
José María Gómez de Salazar is a professor, Maria
Isabel Barrena is a teacher, and Alicia Soria is a
recent Ph.D. graduate with the Materials Science
and Metallurgical Engineering Department at the
Complutense University of Madrid, Spain.
40 µm
30 µm
Figure 11. Detail of a dark slag presented
in Figure 10.
Figure 12. Detail of bright slag presented
in Figure 10.
For more information, contact J.M. Gómez de
Salazar, Universidad Complutense de Madrid,
Facultad de Ciencias Químicas, Department de
Ciencia de los Materiales e Ingenieria Metalúrgica,
Avda. Complutense S/N, Ciudad Universitaria,
28040 Madrid, Spain; +34-91-394-4351; fax +34-91394-4357; e-mail gsalazar@quim.ucm.es.
The inaugural edition of
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JOM • June 2004