An Overview of Iron Provenance and Its Possible Extension

An Overview of Iron Provenance and Its Possible

Extension to Crucible Steel Archaeometallurgy

Meghna N. Desai1

1. National Institute of Advanced Studies, Indian Institute of Science Campus,

Bengaluru, Karnataka ‐ 560 012, India (Email: [email protected])

Received: 06 August 2018; Revised: 19 September 2018; Accepted: 28 October 2018

Heritage: Journal of Multidisciplinary Studies in Archaeology 6 (2018): 926‐944

Abstract: The methodologies in Iron provenance have shown the participation of several intricate

parameters in the manufacturing of iron in bloomery furnace. These parameters have enabled a multi‐

directional examination of iron. Analytical evaluation of assemblages and artefact generated from

smelting experiments have assisted in exploring the correlation between the assemblages. The

contributing factors in the final composition of the iron artefact are studied through various scientific

methods. The research over the years has shown considerable progress in fingerprinting iron artefacts.

This study has attempted to compile an overview of methods implemented and inspecting the possibilities

of extending these methods to crucible steel manufactured from in‐situ carburization.

Keywords: Iron, Provenance, Archaeometallurgy, Crucible Steel, Wootz,

Carburization, Smelting

Introduction Investigating methodologies in iron provenance is an intriguing research among

archaeological and the scientific community in recent years. The initial identification of

iron provenance was mostly speculative with suggestive pieces of evidence followed

by serious scientific investigations in the recent decades. Archaeological application of

techniques like lead‐isotope analysis (Gale et al. 1990), its complementary use with

strontium‐isotope analysis (Degryse et al. 2007), analysis of slag inclusions (hereafter

SIs) (Starley 1999; Leroy et. al 2011 etc.) and Laser Ablation Inductively Coupled

Plasma Mass Spectrometry (hereafter LA‐ICP‐MS) of trace elements (Devos et al. 2000)

have been attempted in course developing various provenancing methods for ferrous

artefacts. The future holds considerable potential in this field turning speculation and

preliminary analysis into a concrete empirical methodology. The necessity of

provenance prevails greatly for artefacts of iron and steel. Substantial methods have

been developed over the last two decades in studying the origin of iron, barely any

have been attempted for provenancing ancient steel. Provenance of such nature can

assist not only in locating the source of production but as the studies have proven, it

can assist in the understanding of the technological process (Navasaitis et al. 2009) and

Desai 2018: 926‐944

927

in the authentication of artefacts. Often these studies lead to a promising provenance

as seen in the case study of Manching (Schwab et al. 2006). Various experimental re‐

constructions were used in the research of iron provenance (Wang and Crew 2009,

Serneels and Crew 1997, Crew 1991, Charlton 2012 etc.) to create reference sets,

isolating variables and correlating certain ratios. The recent questions in steel

provenance are put forward by identifying counterfeits of Viking swords with the

engraving “Ulfberht” with different spellings. These swords are not made of

hypereutectoid steels. Viking swords (between the 9th and 11th centuries CE) with

“Ulfberht” inscriptions have been studied by metallography and are made of

hypereutectoid steels. This hinted at the potential Baltic sea‐Iranian trade route and

the manufacture of this steel somewhere in Central Asia (Williams 2009). Merv, in

Central Asia, was a flourishing crucible steel industry between the 9th‐10th century CE

(Feuerbach 2007) and the trade outlook is quite possible yet only a supposition.

Application of provenance techniques on archaeological remains from ancient crucible

steel making sites can address the questions of extraction, process and geographical

location. The paper aims at presenting a review of iron provenance studies undertaken

and its possible extension to studying crucible steel in India. The study has limited the

discussion to the process and factors involved in the formation of crucible steel ingot

from the ore.

The scientific research on crucible steel in Central Asia (Feuerbach et al. 1997;

Papachristou and Rehren 2002 etc.), India (Rao et al. 1970, Bronson 1986, Verhoeven

1987, Lowe 1989, Lowe et al. 1991, B. Prakash 1990, Srinivasan 1994, 2009, 2017,

Anantharamu et al. 1999, Balasubramaniam 2007 etc.), Sri Lanka (Juleff 1996) and Iran

(Alipour and Rehren 2014) has given promising data of crucible and slags. The

questions on sourcing of raw materials and reconstruction of the accurate

technological process still remain unanswered. The localization of manufacturing

centres is put forth by ethnoarchaeological data (Jaikishan 2007, Srinivasan 2009) and

archaeological probabilities of ore and fuel sources (Griffiths and Feuerbach 1999). A

conclusive methodology is required for definite answers in provenancing crucible steel

to the ore source. The task is challenging as the archaeometallurgical data is scarce and

less likely to avail uniform smelting systems (Blakelock et al. 2009) from a particular

site. The complex processes involved seek substantial archaeo‐chemical studies.

Smelting Chemistry: Key Insights The recent research is focused in implementing conclusive methods for determination

of the geological origin of the iron artefact by studying the chemical composition of its

inclusions (Blakelock et al. 2009) and trace element analysis of the ore, slag and SIs

(Table 1). The ore plays a key role in the manufacture of both iron and steel. Therefore,

it is essential to establish with accuracy the nature of ore used in smelting (Serneels

and Crew 1997). The idea was conjectured by Verhoeven stating a presence of a

certain ore source efficient in making ingots for high‐ quality Damascus blades which

was eventually exhausted and hence the wootz steel blacksmithy declined

(Verhoeven, 1998). Whether there was a certain uniformity in ore source and

Table 1: Reviewed Provenance Literature for Iron

Authors Methodology incorporated Key Outputs of Research

von Bibra (1873) Chemical analysis on iron

objects

No conclusive results due to

lack of technology

R. Pleiner (1950‐

1967)

Metallographic analysis to

study the fabrication process

with chemical analysis

_

Piakwoski (1964,

1976)

Metallographic features +

emission spectrography;

classification of slag inclusions

Optical classification of slags

and put forth the correlation of

carbon and phosphorus. The

technique was innovative with

slim chances of overall

application

Arrhenius (1967),

Thalin (1967)

Provenance intended using

INAA, AES and AAS (referred

Schwab 2006)

Importance of INAA on iron

artefacts

Tylecote (1970;

1990)

Suggested application of

EPMA (electron microprobe

analysis) for study of

inclusions; highlighting the

study of trace/residual

elements in fabrication

techniques and ore source

_

Gale et al (1990),

ZA Gale (1992),

Lead isotope analysis for

provenance

Low Pb content of iron

artefacts, LIA has not been

applied extensively to study

the provenance of iron. Lead

does not participate in chemical

fractionation during smelting

(Further inputs see Degryse et

al. 2007, 2009)

REM Hedges and

CJ Salter (1979)

Identification of elemental

composition of slag inclusions

of Iron Age Iron bars along

with Wavelength dispersive

technique (WDX), Also see S

Paynter (2006)

Seen a systematic pattern in

slag inclusion composition.

Dillmann et al.

(1997)

Microdiffraction techniques

along with a photon

microprobe

Phase identification in 20μm

size of Slag inclusion in Iron

artefacts. See Blakelock (2009).

Desai 2018: 926‐944

929

Buchwald and

Wivel (1998, 2005)

Attempt at establishing a link

between metal phase, its slag

inclusion (slag inclusion

ratios) using optical

microscopy and EDX.

Univariate histograms;

bivariate plots.

Slag inclusion ratios of

SiO2/Al2O3, Al2O3/CaO are

used show potential. The study

was able to differentiate Danish

ores from Scandinavian

artefacts. Phosphorus is found

in high concentration in wood

ashes, P content in slag

depends on slag acidity,

furnace temp and forging

temp. Comparison of oxide

ratio distribution.

Serneels and Crew

(1997)

XRF by Vincent Serneels

(1993) see also Crew and

Salter (1991), Wang and Crew

(2009), Blakelock et al. (2009)

Ratios between trace elements

in iron are influenced by

forging/smithing process which

can be used for ore

fingerprinting.

Starley 1999 Microanalysis of samples

(inclusions and metal

matrices) using SEM based

technology. Metal matrices

were analysed by EDS

Resulted in quantification of

elemental partitioning between

two phases which reflected the

conditions of furnace/hearth.

Highlighting the role of

partitioning in bloomery

furnaces.

Heinmann et al.

(2000)

Could not locate the original

text (in German)

Mn can substitute Fe in slag,

correlation between Mg and Ba

can indicate ore source

(Schwab 2006)

Devos et al. (2000) LA‐ICP‐MS, EPMA for

comparative trace element

analysis

Preliminary analysis of

archaeological objects in

Switzerland, validation of

method with low carbon alloy

steel and cast iron based on

standard references (elemental

composition).

Dillman and

Balasubramaniam

(2001)

Microprobe techniques EDS,

μXRD and μPIXE (for

sampling localised metal/slag

content)

Matching the P composition of

iron pillar with other ancient

iron with P content.

Identifications of slag

inclusions as wustite and

fayalite, homogenous slag

inclusions

ISSN 2347 – 5463 Heritage: Journal of Multidisciplinary Studies in Archaeology 6: 2018

930

Coustures et al.

(2003)

Trace elemental analysis of

slag inclusions to establish

links between ore and iron

bars using ICP–AES/MS and

LA– ICP–MS.

Study conducted on two iron

making sites in France,

development in graphical

approaches, graphical

comparisons of linear

relationships between trace

elements pairs and data

matrices of known data sets.

Incompatible trace elements

remain homogenous regardless

the kind of slags.

Schwab et al.

(2006)

Metallography (Schwab 2002),

SEM‐EDX, electron

microprobe, Quantitative

analysis of iron matrix and

slag inclusions by WDS, Ore

samples by WD‐XRF, ICP‐AES

and AAS, bulk concentration

of iron artefacts by ICP‐AES

and AAS, lead isotope ratios

of ores by ICP‐MS

Major elements found in SIs

have no correlation with ore‐

iron chemistry. Separation

technique incorporated to

prevent interference of iron

with lead isotope measurement

in Argon plasma. Logarithmic

diagrams used in illustrating

trace element patterns of ores

and metals. Certain element

ratios not changed during

smelting.

Paynter (2006) SEM‐EDS on smelting slags

from various parts of Britain, a

data sheet of analysed

smelting slags from previous

studies, calculation of FeO

content using stoichiometry.

Potential of smelting slag and

slag inclusions using data

from Hedges and Salter (1979)

Elaborate details on ore and

types of ore, types of wood

used for making charcoal and

its importance in smelting,

temperature, furnace line

interaction with high grade

ores etc. Since slags are

abundantly found at

archaeometallurgical sites, the

study finds great deal of

potential in provenance.

Desaulty et al.

(2008)

ICP‐MS (wet acid digestion) +

INAA + XRD (phase

determination in ores)+ SEM‐

EDS (bulk analysis of

heterogeneous samples)

Disadvantages of INAA, Co,

(Ni), Rb, Cs, Ba, La, Ce, Sm, Eu,

Yb, Hf, Th, U in the ores, slag

and Iron can be successfully

determined. Ni could be due to

use of Ni sampler in INAA.

Use of Pt. cones to limit Ni

contamination.

Desai 2018: 926‐944

931

Degryse et al.

(2003), (2007)

Lead and Strontium isotope

analyses by TIMS (Thermal

ionization mass

spectrometry). ID‐TIMS for Sr

concentrations and Pb

contents using respective

enriched tracer solutions.

Iron artefacts can be

determined by Sr‐isotopes

which complements the

limiting factors of Pb‐isotope

and with greater certainty and

precision. Capable to

differentiate chronological

groups of iron provenance and

source of raw material.

Identifying Camoluk as a

promising ore source for

unidentified ore source in

Degryse (2007).

Dillman and

Héritier (2007)

SEM‐EDS (SI composition),

quantification of oxygen from

elemental composition

Perform analyses of numerous

artefacts, followed by

metallographic inspection.

Introduction to Non‐Reduced

Compounds and their

unchanged ratios with same

ores. NRC ratios seem to

indicate a common origin. See

Dillman et al. (2005).

Wang and Crew

(2009)

Compositions of metals and

Slag inclusions using SEM‐

EDX (three experimental

knives, one blade from

Krakow. See Crew (1991)

The phosphorus content in the

metal is not a representation of

its ores. Partitioning of P

between metal and slag is

affected by the blowing rate.

Blakelock et al.

(2009)

Studies of SI and slag measure

by SEM‐EDS, metallography

(iron samples), bivariate plots

used. Materials from Crew

(1991) selected for bulk

chemical analysis.

Al2O3/SiO2, Al2O3/MgO,

Al2O3/K2O, and Al2O3/CaO

ratios were lower in the object

SI compared to tap smelting

slag. Case study at Hammeh

and Tel Beth Shemesh. Objects

made in different smelting

systems had a possible

comparison between their

Al2O3/SiO2 ratios. Composition

of SIs is closest to the smelting

slag

Navasaitis et al.

(2010)

Elemental composition of ore

and slag by OES, iron by SEM‐

WDS, metallography

Discussion on segregation of S,

Co, As, P. Use of controlled

smelting operations to facilitate

reduction of S and P.


932

Leroy et al. (2012) Elemental composition using

SEM‐EDS. Bulk composition

using (Desaulty 2008):

INAA+ICP‐MS, data sets

implemented, multivariate

methods incorporated to

compare elemental signatures

Needs collection and treatment

of large data which will enable

better discrimination with

provenance. The method has

the potential to authenticate of

a known provenance and the

scope for trace elemental

analysis along with

multivariate analyses in this

area of study.

Charlton et al.

(2012)

Bulk composition analysis

using SEM‐EDS, MS‐EXCEL

(computing data), R 2.11.1

Exploring chemical signatures

between bloomers slag and SI

in iron. Oxide ratios,

comparison of MnO and TiO2.

The literature that was written in languages other than English, whose translation

could not be found was omitted for this review bearing in mind possible errors in

translation and incorrect interpretation.

processing is unclear. Some of the earlier studies on iron archaeometallurgy in India

has highlighted ore beneficiation1 (Hegde 1973). Similar methods of ore preparation

were adopted in Nur, Iran during the making of cast iron (Craddock 2007). The ore

depending on its source of origin accounts for 77.5%‐100% of the composition of the

slags and slags derive bulk of its composition from the ore, but the slag composition is

also dependent on ceramics and fuel ash (Crew 2000). The contents of the ceramics are

exchanged when the slag attacks the inner furnace walls and tuyeres (Veldhuijzen and

Rehren 2007, Charlton et al. 2012). According to Coustures et al, the trace element

composition when altered by clay and charcoal, the variability is small and the

correlation coefficient is acceptable (Coustures et al. 2003). The ash content of charcoal

will not affect the crucible steelmaking but will affect the wrought iron manufactured

prior to the making of the steel.

Studies have been carried out in establishing the relationship of SIs with smelting slags

and ore from archeometallurgical sites. Chemical and phase compositions of these

inclusions were studied for fingerprinting (Hedges and Salter 1979, Buchwald and

Wivel 1998, Madsen and Buchwald 1999, Héritier et al. 2013). Using trace elements for

provenance studies require a careful selection of elements used. Their concentrations

may be insignificant, but, they can possibly play a role in altering the microstructure of

a metal and its properties (Navasaitis et al 2009). Establishing a simple relationship of

trace element concentrations in ores, slags and artefacts is not accurate because of

chemical fractionating, NRCs (Non‐reduced compounds), their distribution and

refining treatment of the artefact. The preference of elements depending on their

affinities for metal or slag or the other can be estimated from Richardson‐Ellingham

diagrams (Serneels 1993, Schwab et al. 2006). The elements that are siderophile trace

elements like Co, Ni, Cu or As are the most important trace elements in bloomery iron

Desai 2018: 926‐944

933

(Navasaitis et.al; 2009) are mostly reduced to metal and depleted from smelting slags

(Serneels and Crew 1997). Lithophilic elements along with some iron enter the slag.

In this case it becomes incorrect to compare just the siderophile elements with the iron

ore and the post‐smelting metal shows an enhancement (Wang and Crew, 2009) in

siderophile elements compared to the ore. The trace elements are also influenced by

refining and working making it difficult for identification of ore source (Serneels and

Crew, 1997). With more refinement during forging the rate of newer SIs rises

(Dillmann and L’ Héritier, 2007) The research on fractionation of trace elements in the

bloomery smelting is still unclear (Schwab 2006). Incompatible trace element

concentration in all ore types remain constant and homogenous in slag whereas the

chemical signature of starting ore distributed to various slag types is Ba/Sr, Rb/Cs,

Zr/Hf, Zr/Th and Hf/Th (Coustures et al. 2003).

During an experimental smelt carried out in Lithuania (Navasaitis et al. 2009) the

resulting iron showed high phosphorus content whereas in antiquity, though, the iron

was smelted from high phosphorus ores (bog ores) the smelters were able to produce

good quality iron. It is quite possible that smelters found a way to control phosphorus

content either by addition of flux or other possibilities of ore and charcoal chemistry

that may have been overlooked.

In making of crucible steel through in‐situ carburisation the role of charcoal and

furnace lining can be neglected as the crucible provides a closed environment.

However, crucible lining may interfere with the wrought iron. The use of high

refractory clay (Lowe 1989, Srinivasan 2007) in making the crucible can withstand high

temperatures, may not show any exchange of composition but only undergo

vitrification. Such clays are reported from Konasamudram (Phani 2014), Telangana

(18°44’N, 78°31’E). It is unclear at this stage whether the slag inclusions are present in

the wrought iron introduced in the crucible for steelmaking and the extent of

consolidation that was carried out for the bloomery iron. If the glassy slag is present in

the wrought iron in high carburised sections and in all steel, it shows elevated trace

element concentration (Schwab et al. 2006).

From the same ore type; different slag compositions are produced at different

temperatures (Lychatz and Janke 2000, Schwab et al. 2006). It is quite possible that the

distribution of elements, the rate of distribution, NRCs and volatile impurities are

solely depended on the temperature. This could aid in answering wasteful primitive

iron smelting (Hegde 1973) and high amounts of iron in the slag. Lower temperatures

in the furnace or anywhere within the furnace have the weakest redox reactions and

due to this the slag shows greater proportions of FeO plus other reducible compounds

(Charlton et al. 2012). This lack of higher temperature attainment could result in

Dhatwa2 (Hegde 1973) smelting; the wastage of iron. It is extremely important to

understand the thermodynamics of the furnace and the progression of its CO/CO₂

ratios (Prakash 1991).


934

Crucible Steel: Possibilities in Establishing the Relationship

between Ore‐ingot (In‐situ Carburisation) Crucible steelmaking was incorporated in order to completely melt the wrought iron

and homogenise carbon content allowing slag particles to float on the surface for easy

removal, manufacturing a high carbon steel with negligible inclusions (Anantharamu

et al. 1999). Two different kinds of processes3 are known through travelogues and

scholarships on the manufacture of wootz steel, whereas one is known to mention a

direct smelting of steel from the ore (Schwarz 1901, Verhoeven 1998). This discussion

is limited to the in‐situ carburisation process of wootz making. The thermo‐chemical

reactions within the crucibles are completely independent of the furnace fuel and

furnace lining. The crucible lining could play a contributing factor in the slag and the

ingot chemistry, however, the refractory nature of crucible may change the interaction

dynamics which will be dealt with in another study. Comparisons of Indian crucibles

already has been attempted with those found in Ferghana valley (Rehren and

Papachristou 2003). Crucibles at Merv were found to contain prills and residual charge

present in crucible slag (Feuerbach 2007). Similar observations were made Mel‐

Siruvalur (Srinivasan 1994, 2009 and 2017) and Hyderabad (Lowe 1989). The analysis

of these prills representing the ingot is still under speculation. The ingots are scarcely

available for analysis and few studies have been published on the characterization of

ingot making it difficult to comment on the nature of inclusions (if any) and

segregations. Verhoeven (1998) mentions wootz ingots showing microsegregation

from which the Damascus blades were forged. The ingot analysed by Smith (Smith

1960) showed a composition of 1.34% C and the etching of the ingot cross‐section

revealed a dendritic pattern.

The Damascus sword analysed showed varying carbon percentage (Santos et al. 2015).

The pattern was due to the microsegregation of an impurity element. Considerable

impurity levels of P, Mn, S and Si were found in Damascus steels and the pattern of

Smith’s ingot resulted possibly due to the microsegregation of Phosphorus

(Verhoeven, 1987). Such patterns in microsegregation can be used as markers for

provenance, but, since the ingot data is limited this method may prove challenging.

Moreover, phosphorus (above 0.1%) promotes the formation of cementite (Brian and

Gilmour, 2001) and its role in band formation of crucible steel artefact still remains

inconclusive (Barnett et al. 2009). There is an ore and artefact characterization

attempted at Ghattihosahalli by Sambasiva Iyer in 1898‐9 reporting traces of sulphur

and phosphorus in the hematite ore. Later, in 1990s samples of wrought iron, a piece

of steel (from an ingot?) and slags were characterized. A sample from the edge of the

piece of steel which seemed like an ingot was collected by Anantharamu to be

examined in Edmonton and another sample from the interior was examined at GML,

Bangalore. The carbon content was not homogenous. The carburisation only

penetrated the outer regions (0.69% C) that lowered the melting point of steel. The

interior was still solid wrought iron with its original carbon content (no solid state

reduction took place). The metallographic structure of a section from centre was found

Desai 2018: 926‐944

935

to be of ferrite grains with streaks of pearlite with less phosphorus content. Similar

results were reported by Rao et.al for an ingot from Salem of composition 0.45% C,

higher at the surface than at the centre (Verhoeven 1987).

The study of crucibles by Rao et al. mentioned the presence of cristobalite (a silica

polymorph at high temperatures), which is strong evidence in favour of crucible steel

furnaces attaining the temperatures above 1400°C debunking the temperature

argument in crucible steel furnaces. The ingot failed in attaining carburisation‐

possibly due to faults in lid or the crucible. The material technology for making

crucibles, baking and the presence of rice husk inclusions was more or less common

across the south Indian crucible steel making sites (Lowe 1989, Srinivasan 1994). It is

important to note that charge had to be completely molten for the air blast to stop

(Verhoeven 1987). Wherever, the charge failed to melt completely, the crucibles were

rejected (Voysey 1832; Heath 1839 and Coomaraswamy 1956). An iteration of such

precision could aid in provenancing of crucible steel samples. Complex annealing

process and working techniques were incorporated post the formation of the ingot

which will be dealt with elsewhere. (Voysey 1832; Heath 1839; Schwarz 1901). It is

evident that the formation of bloomery iron in the furnace is depended heavily on the

maintenance of temperature conditions and formation of iron referred in the

Boudouard equilibrium. Following reversible equations show the altering CO/CO2

ratios at different temperatures. At temperature, after 1300°C more than 99% of CO2

will convert into CO (Figure 1). At around 750‐800°C, Iron converts to Iron oxide, in

order to melt the slag, the temperatures must be increased to somewhere between

1200°C‐ 1300 °C.

3Fe2O3+CO ⇔ 2Fe3O4+CO2

Fe3O4+CO ⇔ 3FeO+CO2

FeO+CO ⇔ Fe+CO2

2CO ⇔ C+CO2

Factors other than temperature that affects the ingot chemistry include the bloomery

iron composition and the composition of carbonaceous matter that is placed inside a

crucible. The extent of smithing of bloomery iron into wrought iron and its C% needs

to be identified before heating it is crucible is crucial to understand. The role of slag

inclusions (SIs) and their participation in ingot chemistry can then be commented. The

secondary smithing of bloom involved heating in a forge hearth to 1100‐1200°C. Mix of

silica sand and iron ore powder (iron oxide?) was sprinkled on the bloom to increase

the fluidity of slag, once the slag was fluid the bloom was taken out to be forged (hot

forging) and these steps were repeated until all the slag was removed, pores of the

metal were closed and the target density was acquired (Prakash 1991). During the

secondary smithing, a considerable amount of metal is lost to oxidation. An oxidised

layer forms on the metal surface as it is being worked. Addition of flux like sand rich

in silica facilitates the formation of fayalite slag and removal of Iron oxide (Blakelock

2009). The imperfections of secondary smithing may introduce secondary inclusions


936

(Blakelock 2009) which may be overlooked in wootz production if the wrought iron

does not undergo secondary smithing. The microstructure of the refined wrought iron

showed some inclusions and certain porosity (Prakash 2011). It is possible that the

production of wootz ingots was independent of the wrought iron content and its SIs.

Complete melting of contents inside the crucible and the separation of slag from the

molten iron facilitated a good quality hypereutectoid steel free of inclusions

(Anantharamu et al. 1999).

Figure 1: Fe‐C‐O Equilibrium Diagram: Boudouard’s Equilibrium

(Yingxia Qu et al. 2015)

Amongst the data provided (Prakash 1991) on analysis of wootz steel objects, there

appears to be an uncombined carbon of 0.31% in one of the object4. The formation of

smelting slag both from bloomery furnace and the crucible need to be characterized.

The likeliness of finding the data from one site is slim, however, Konasamudram,

Ghattihosahalli and Dhatwa (for iron) show promising data if the theoretical

assumption of technical processes stay uniform. The following equation can be

considered for studying the final composition of the ingot which a treatment of

wrought iron with the carbonaceous matter to form a wootz ingot.

Cingot = (W+B+Lc)‐(V+S)

[Assuming no flux (F) was added. Glass as a flux was mentioned to be used in co‐

fusion process (Voysey 1832)].

Desai 2018: 926‐944

937

Where Cingot = chemical composition (major and minor elements+segregation) of the

ingot, W= wrought iron composition (smelted from a previous bloomery process), B=

composition of carbonaceous matter, Lc = the exchange with crucible lining, V= volatile

impurities and S= crucible slag. (See L and V)5.

Figure 2: Factors Involved in Manufacture of Crucible Steel through in‐situ

Carburisation

Trace elemental analysis of ratios by LA‐ICP‐MS (rare earths and siderophile

elements) of elements does have certain potential in the provenance of crucible steel

(Figure 2). However, until the chemical fractionation and element affinity is

completely understood; it cannot be the only conclusive method for analysis. LA‐ICP‐

MS facilitates direct solid sampling and avoids the contamination risk in solid

sampling. Both ICP‐MS and INAA are suitable methods for macroscopic analysis

(Desaulty et al. 2008; Leroy et al. 2012). Metallography, beyond a doubt, has proved

useful in understanding the technological processes and in this case, with

microsegregation. Ion beam techniques like PIXE (Particle Induced X‐ray Emission)

and INAA can aid in comparative analysis, both techniques are expensive but non‐

destructive. The non‐destructive characterisation of Damascus blade by Santos et

al.(2015) using PIXE showed the same results as those reported by Peterson et al.

(1990) using destructive analysis on the swords. The former showed the independence

of sword hardness from the carbon content and a vital role of elements in low

concentrations (<100 ppm) like Mn, Cr, Ni and Cu in the formation of crystal

structures. Although, it is not in the interests of this paper to establish connections

between ingot and Damascus blades due to the extensive forging and refining

parameters that demand consideration. However, establishing an ore‐ingot

relationship will prove useful for further artefact provenance. XRD (X‐Ray Diffraction)

and pXRD (Powder X‐Ray Diffraction) can be used in identifying phase change

(Desaulty et al. 2008) in the ore and slag. Lead isotope data from the peninsular region


938

of India is scanty and due to this lack of database, the radiogenic isotope methods can

be inconclusive (Srinivasan 2013). Lead and strontium isotope analysis need thorough

understanding of geochemistry of Indian ores in order to be proposed for this study.

Conclusion Provenance of iron and steel is crucial to understanding of ferrous archaeometallurgy.

It is an amalgamation of several technologies like those of ore beneficiation, refractory

ceramics, refining and forging, thermo‐chemical perspectives and human skill. The

simulations and reconstructions of the archaeometallurgical processes have paved the

way for generating data sets of known parameters aiding in the understanding

chemical fractionation and ore, slag and artefact correlation. Ion beam techniques

complemented with spectrometry methods can show promising results, however, trial

and errors of newer methods must continue. The study of iron provenance is both

challenging and exhausting. These studies are essential to understand the economy of

the ancient world, their technology and trade networks. A provenance study of iron

and steel needs to be commenced systematically in the Indian iron and steel context,

acknowledgement of its challenges and aim at overcoming them using advances in

modern science. A review of the techniques for iron and larger overview of

influencing factors for manufacture of wootz steel ingots are mentioned in this paper

in a hope to explore them eventually, stepwise, through upcoming studies. Since the

data and resources are limited; implementation of collaborative studies will

accumulate better results.

Acknowledgements The author would like to acknowledge the contributions of all the archaeologists,

archaeo‐scientists, metallurgists and material scientists in provenance of iron, data

compilation and analysis, experimentation and analysis of ancient iron, steel and

ceramics. The author would also like to thank Prof. Sharada Srinivasan for her

encouragement and inputs and along with Prof. Kenoyer for giving an opportunity to

participate in iron and wootz steel smelting experiments.

Notes 1 (Roasting‐ removal of water, CO2 and other volatile components) used in the conversion of limonite

and hematite, increasing its iron oxide content, porosity and easy pulverisation for reduction.

2 An early historical site in Gujarat.

3 Co‐fusion process and in‐situ carburisation. (See: Lowe 1989, Srinivasan 1994, Srinivasan and

Griffiths 1997, Feuerbach 2007, Craddock 2007).

4 This reaction has been used in producing graphite as well as producing carbon nanotubes (Dai et. al

1996). The crucibles were highly graphitized (Prakash 1991).

5 The variables ‘V’and ‘Lc’ ʹ(changed from furnace line ‘L’ by adding a subscript ‘c’) are left to be same

as given in the Cslag equation by Charlton et al. (2012) to avoid confusion.

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939

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An Overview of Iron Provenance and Its Possible Extension