Aronson Et Alii - Archaeometallurgical Investigation of the Iron Anchor From The

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Archaeometallurgical investigation of the iron anchor from the

Tantura F shipwreck

A. Aronsona, D. Ashkenazia,⁎ , O. Barkaib, Y. Kahanovb

aFaculty of Engineering, Tel Aviv University, Ramat Aviv 69978, IsraelbLeon Recanati Institute for Maritime Studies, University of Haifa, Haifa 31905, Israel

A R T I C L E D A T A A B S T R A C T

Article history:

Received 1 November 2012

Received in revised form

6 January 2013

Accepted 14 January 2013

TheTantura F shipwreck was a coaster or a fishing vesselabout 15.7 m long, discovered in the

Dor/Tantura lagoon, Israelin 1995. It was datedto between the mid-7th and the endof the 8th

centuries CE. Among the finds excavated were two T-shaped type iron anchors. Of the two

anchors, one (anchor A) was thoroughly studied by archaeometallurgical methods in order to

identify forge-welding lines, to determine the welding quality and to understand the

manufacturing technology. The examinations included X-ray radiography, XRF analysis,

optical microscopy, SEM/EDS observation and analysis, OES analysisand microhardness tests.

The investigation included characterization of the composition, microstructure, thermal

treatments, forge-welding junctions and slag analysis. The results revealed a heterogeneous

microstructure, rich in glassy, fayalite and wüstite slag. Iron based phases included ferrite,

pearlite, cementite and Widmanstätten plates, all typical to wrought iron. The forge-welds of

Anchor A were located. Each arm was made of one piece, weighing about 2.5–3 kg and the

shank was made of a few 1.5–2 kg pieces. The second anchor (anchor B) was only briefly

examined visually and with a few radiographs, which support the results from anchor A.

The research results revealed significant information about T-shaped anchors and their

manufacturing process, including hot-working processes without any additional heat

treatments, and folding techniques. The microstructure was similar to other ancient simple

tools such as saws, sickles, axes and mortise chisels, and though the technology to make

complicated structures and objects, such as swords, existed at that time, the anchors did not

requirethis sophistication; thus simplertechniqueswere used, presumably becausetheywere

more cost-effective.

© 2013 Elsevier Inc. All rights reserved.

Keywords:

Archaeometallurgy

Iron

Microstructure

Tantura F

T-shaped anchor

Wrought iron

1. Introduction

The Tantura F shipwreck is the remains of a coaster or a fishing vessel about 15.7 m long. It was discovered in 1995, about 70 moffshore in Dor (Tantura) lagoon, which is located on theMediterranean coast of Israel, south of the ancient Tel Dor,about 25 km south of Haifa. It was found in about 1 m of water covered by about a 0.85 m layer of sand, the thickness of whichchanges due to sea conditions. Tantura F was excavated during

five seasons in 2004–2008 [1–3]. Based on both 14C and ceramic

typological analysis, the shipwreck was dated to between themid-seventh and the end of the eighth centuries CE—the localearly Islamic period [2]. Among the finds exposed in theshipwreck site were two T-shaped iron anchors—anchor Aand anchor B (Fig. 1). Anchor A was found beneath the hull,touching it (Fig. 1a), while anchor B was found concretedto the external part of the planking remains below the hull(Fig.1b). The anchors were found covered bya thickgreylayer of

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⁎ Corresponding author at: School of Mechanical Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel. Tel.: +972 3 6405579;fax: +972 3 6407617.

E-mail address: [email protected] (D. Ashkenazi).

1044-5803/$ – see front matter © 2013 Elsevier Inc. All rights reserved.http://dx.doi.org/10.1016/j.matchar.2013.01.004

A v a i l a b l e o n l i n e a t w w w . s c i e n c e d i r e c t . c o m

w w w . e l s e v i e r . c o m / l o c a t e / m a t c h a r

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encrustation and concretion composed of sea sand, shells andsmall stones. Both were broken at the shank, with part of theshank and the anchor cable ring missing.

The present study is part of a systematic series of

investigations concerning the Tantura F shipwreck (e.g., [1–

3]).According to Eliyahu et al. [3], the connection of the anchors tothe wreck of Tantura F is based on their location at the site andtheir typology, considering the date of the shipwreck. Anchor A's typology was similar to anchors B and to other similar anchors such as the anchors found in the Yassıada I shipwreck[4]. The anchors were under the ship, which rules out thepossibility that they were droppedafter the wrecking of TanturaF. If the anchors had been dropped by a vessel earlier than theTanturaF, they would probably have sunk deeperinto the sand,as a result of the activity of the sea, including waves, currentsand sand movement inside the lagoon.

The anchors were removed from theseabed to thelaboratory:

Anchor A in the third season (2006), and anchor B in the fourth

season (2007). After documentation and X-ray radiography,the concretion layers were removed carefully, while watching the radiographic images in order to cause minimum damage tothe metal remains of the anchors. The cores of the artifacts

were revealed: despite the heavy concretion and the oxidationprocess during 1300 years underwater, the metal survived ina good state of preservation—a hard core of iron was evident(Fig. 2 for anchor A). The arms of both anchors had a rectangular cross-section and were not precisely perpendicular to the shank.Their tips were flattened and the cross-sections of both shankswere circular, which is unusual for a wrought iron object, butcharacteristic of T-shaped iron anchors [3].

A wide variety of anchors in shape and material were usedin antiquity, late antiquity, Byzantine (local), Early Islamic(local) and Middle Ages. They were developed according tothe technological knowledge, capabilities, and experience, aswell as requirements, considering the size of the vessel, and

the nature of the ground, weather and water conditions [5].

Fig. 1 – The Tantura F shipwreck anchors covered with thick encrustation and concretion: (a) anchor A and (b) anchor B.

Fig. 2 – Anchor A: (a) covered with a thick concretion, (b) illustration of the iron remains, relative to the concreted artifact

(estimated superposition, not a real cut) and (c) after the concretions layers were removed.

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A typological–chronological analysis of iron anchors, based onanchors discovered up to the 1980s, was suggested by Kapitän[6]. The earliest type of iron anchor had straight arms inV-shaped position and was dated to Roman Republican times.The earliest T-shaped anchors to be discovered were exca-vated in the Dramont D shipwreck, France, dated to the firstcentury CE and the Dramont F shipwreck, dated to the second

half of the fourth century CE [6–9]. The last version of ironanchors (in Kapitän's typology) was the Y-shaped anchorswhich are dated to the 10th and 11th centuries [10,11].However, T-shaped anchors were found in the Çamaltiburnushipwreck assemblage, dated to the thirteenth century [12].

According to Kapitän, typological–chronological develop-ment of T-shaped anchors over the years can be distinguished[13]. The first T-shaped anchors had a rectangularcross-sectionshank and stock, and they appear to be a transitionbetween theRoman and the Byzantine types. The second type is character-ized by long straight flukes and relatively short arms, bentslightly upwards, anda round holein theshankfor a detachablestock (similar to the early anchors discovered in the Dramont F

shipwreck). The latest type, which was discovered in theYassıada I shipwreck, dated to CE 625, is characterized byupward-curved flukes bent outwards, longer arms and a roundhole for the stock in a rounded cross-section shank [4].

In summary, theuse of T-shaped iron anchorswas commonthroughout the Mediterranean, Marmara and Black Seas over aperiod of approximately 1200 years, starting from the firstcentury and lasting to the thirteenth century. At the beginning of this period, they were present in parallel to curved armedanchors, while from the tenth century they appeared together with Y-shaped anchors. However, it is difficult to establish adetailed typological development.

Analysis of one T-shaped iron anchor from the Yassıada Ishipwreck revealed that it was forged-welded, almost clear of slag, had a carbon content of 0.07 wt.% and small amountsof other elements: Co (1.0 wt.%), Ni (0.50 wt.%), Zr (0.50 wt.%),K (0.06 wt.%), Si (0.14 wt.%), Al (0.05 wt.%), Cr (0.10 wt.%), S(0.01 wt.%), Na (0.01 wt.%), Mg (0.01 wt.%), Ca (0.01 wt.%), Ti(0.01 wt.%), V (0.01 wt.%) and Mg (0.01 wt.%) [3,14].

Analysis of the manufacturing process of anchors by welding about 16 pieces of iron, the largest weighing 5–6 kg, is describedin the report of the Y-shaped anchors of the eleventh centurySerçe Limanı shipwreck [10]. Analysis of the iron is given as well[15].

In a previous study of the anchors of Tantura F, the forge-welding lines could not be detected [3]. It was thereforesuggested that further work should be performed, including detailed radiography and further metallographic examinationof sections from other parts of the anchors, as well asextended element slag inclusion study.

The present study is thus an extended investigation of theTantura F anchors. It aims to determine the manufacturing processes of the anchors, focusing on the forge-welding processes of anchor A and identifying the locations of theforge-welding lines and their quality. The importance of thisresearch is due to its comprehensive metallurgical andchemical analysis which was done over the entire anchor A.

A significant part of this work was the development of aresearch methodology for investigating large archeologicalartifacts that were suspected to have been assembled from a

number of wrought iron blooms that were forged weldedtogether. The research development methodology is based onknowledge that has been borrowed from forensics science andfailure analysis methods.

Since these anchors are dated between the mid-seventhand the end of the eighth centuries CE, it is logical that other T-shaped anchors from the same period were manufacturedusing similar methods. Thus, the present analysis can serveas a tool in future studies of similar artifacts.

2. Background of the Metallurgical Analysis

2.1. The History of iron Manufacturing and Processing

Since the melting point of pure iron is around 1540 °C, whichcan be reached only with nineteenth century technology,ancient iron was produced at lower temperatures in a reducing atmosphere using the smelting process. The main method for smelting iron ores was the ‘direct’ or ‘bloomery’ method, inwhich the ore was inserted into a furnace with carbon-rich fuel,at temperatures up to 1200 °C. In this process, the iron never reached the melting point, but as iron oxides reduced, the orecoalesced as a solid mass of metal called the ‘bloom’ and the

slag was separated as a melt. Then the slag-rich sponge wassubsequently hot worked (forged) to squeeze the slag out and toconsolidate the iron, producing wrought iron [16]. According tofurnace limitations, the ancient bloom was usually small andin order to form a ship's anchor, several small blooms, a fewkilograms each, were forge-welded together [17].

The basic furnace was a cylindrical clay shaft, withdetentionsof between 1 and2 m in height, an internal diameter of between 0.3–l m and walls normally over 0.2 m thick, toreduce heat loss andairinlets, called ‘Tuyeres’ or blowing holes,which were located about 0.3–0.5 m from the furnace base.The commonest form of fuel was charcoal. In most furnaces, anarch through the wall of the furnace enabled the slag to beremoved, either cold or as tapped slag.

Fig. 3 – The ‘straight scarf weld’ and the ‘cleft weld’ [20].

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At the beginning of the smelting process the furnace wasfirst charged with fuel, then preheated. When it was hot, amixture of ore and charcoal was inserted into the furnace andair was pumped into it. The iron ore was initially reducedinside the furnace at temperatures of around 800 °C whereas

slag was formed near the base of the furnace at temperaturesover 1000 °C. The major reactions occurring during smelting are: (1) the reduction of iron oxide to metallic iron, and (2) theformation of a liquid slag. During the first reaction, carbonmonoxide (CO) was formed by a reaction between the carbonpresent in the fuel and the oxygen in the air. During the second reaction, liquid slag, such as wüstite (FeO) andgangue oxides (silica, alumina, etc.), was formed. The slag wasseparated from the metal by allowing the liquid to slap to thebase of the furnace and then by removing it. If the furnacetemperature was not high enough, the separation wasnot completed successfully and the bloom was composed of metallic iron mixed with slag. The blooms were oftenheterogeneous, varying in composition from pure ferriticiron, phosphoric iron (up to 1 wt.% P) to carbon steels(containing up to 0.8 wt.% C). In order to reduce the amountof included slag, the bloom was broken up by hammering,separating the ductile iron from the rest of the material.The hammering removed the majority of the semi-fluid slag and oxides and then, the iron particles were welded together to form a ‘bloom iron,’ producing iron with some slag [18].The ‘bloom iron’ could be then worked up into different ironobjects by its smelter or sold to another blacksmith.

Iron smiths had different alloys available to them, including pure and soft ferritic iron, harder and more brittle phosphoriciron, and steels with varying carbon contents, enabling thefabrication of hard and tough edges. The main techniques used

by the smith were cold working, hot working, forged-welding and heat treatments. In cold working (also known as workhardeningand strain hardening), the metal is deformed at a lowtemperature, strengthening the metal by plastic deformationwhich displaces dislocations and slightly hardens the iron.

In hot working the metal is deformed above its recrystallizationtemperature (over 600 °C in the case of iron), enabling the smithto easily shape the metal. Forged-welding joins two metal partstogether by heating them to high temperatures andhammering them together. In heat treatments, the metal is heated toimprove specific properties. For example, steel canbe made veryhard (and brittle) by heating it to 900 °C and then quenching it incold water. However heating the metal increases the possibilitythat the metal will oxidize and become useless. This can bepreventedby controlling thefire and by fluxing themetal surfacewith sand [19].

2.2. Forge-welding Techniques

Forge-welding (also called fire welding) is a process wherebytwopieces of wroughtironare joined together by a combinationof thermal and mechanical methods (such as hammering),without the addition of a solder. When wrought iron is heatedup to 1350 °C, it can be easily forged-welded by hammering.The process must be completed before the iron joint coolsbelow 1050 °C [18]. The iron silicate in the slag, left over fromthe smelting or added during sand fluxing [19], facilitatesthe welding by inhibiting corrosion, which is faster at hightemperatures [18].

There were two basic techniques for welding two partstogether: the ‘straight scarf weld’ and the ‘cleft weld’ [20], asillustrated in Fig. 3. Using these techniques, the welded contact

Fig. 4 – Images of T-shaped anchors from the Tantura F shipwreck: (a) anchor A, (b) anchor B.




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area is bigger and the pressing force from hammering is moreeffective, resulting in better forge-welding [21]. Therefore, inthe case of connecting two blooms that were shaped as rods,

such as the shank and the arms of the anchors (that wereconstructed from several pieces), it is expected to find similar forge-welding forms of joints—straight scarf or cleft weld.

2.3. Previous Study of the Iron Anchors from the Tantura

F Shipwreck

Eliyahu et al. [3] previously studied the two anchors (Fig. 4),but only analyzed two different zones of each anchor. These

zones were analyzed by typological and archaeometallurgicalmethods, including radiography, metallographic cross-sections,SEM with EDS analysis, Optical Emisson Spectroscopy (OES)analysis and microhardness tests. They found a heteroge-neous microstructure in both anchors, consisting of ferrite,Widmanstätten ferrite-pearlite plates and pearlite, whichare typical phases and morphologies in wrought iron

made by the bloomery process. Combining their OES andSEM/EDS results, they suggested that the anchors had a similar composition. Soda-blast cleaning followed by chemicaletching revealed lines suggesting the presence of forge-weldments [3].

Eliyahu et al. [3] concluded that since both anchors had thesame minor elemental inclusions (except for phosphorousthat appears in the inclusions from Anchor A only) and sinceanalysis of minor and trace elements present in individualinclusions should reflect the elements present in the originalore, the two anchors were probably manufactured by thesame process and from the same ore. They assumed that apoor quality weld could be detected by radiography, whereas a

good forge-weld might not be easily detected by radiographynor observed by an Optical Microscope (OM) and Scanning Electron Microscope (SEM). Since the radiography imagesshowed no sign of welding lines in both anchors, and sincethe representative metallographic images showed no forge-welding lines, and no unique amount of oxide or glassyinclusions were observed in all sections, they concluded thatthe T joints of the anchors had probably been welded veryprofessionally by a very highly skilled blacksmith who wasable to avoid bulk defects in the forge-welding process. Inaddition, the metal survived in a very good state of preser-vation: the shank was found with a core of about 5 cmdiameter of unoxidized iron. This might have been a result of environmental conditions—the anchors of Tantura F hadbeen buried under a layer of sand about 1 m thick. Accord-ingly, they assumed that the only way to observe goodforge-welding is by slightly etching the surface of the anchorsand then observing the result. Eliyahu et al. [3] suggest thattakinginto account theweights of theartifacts and themacroforge-weld lines, with regard to the manufacture of bothanchors, it may be suggested that anchor A and B were madefrom at least four pieces.

3. Experimental Methods and Tests

Since anchor A had less corrosion than anchor B, thepresent research focused on anchor A, identifying thelocations of its forge-welding lines and evaluating itswelding quality. Anchor A was analyzed by its typologyand by archaeometallurgical methods, including radiogra-phy, Stereo-microscopy (SM), metallurgical Optical Microscopy(OM), SEM (Jeol JSM-7000F field emission SEM, with a voltageof 25 kV), Energy Dispersive Spectroscopy (SEM/EDS), X-rayfluorescence spectrometry (Thermo Scientific Niton XL3T 900handheld XRF analyzer, with a geometrically optimized largearea drift detector technology), Optical Emission Spectroscopy(Baird HR-400 instrument), Vickers microhardness test. Anchor B was analyzed only by its typology and by radiography(Table 1).

Fig. 5 – Anchor A: (a)sectional plan (cylindrical hole at thecentre

of the anchor was made by Eliyahu et al. [3] during the

preliminary study), (b) parts of anchor A after cutting.

Fig. 6 – Forge-weld lines at the throat (shank-arm junction).


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X-ray radiography was performed in different locations andprojections of both anchors in order to reveal thelocations of theforge-welding lines and the welding quality, using a GE-ERESCO

MF3 300 Kv X-ray tube, with 200–250 kV working voltage,3.5–4.5 mA working current and exposure time of 2.5–4.5 min.

The dimensions and mass of both anchors were measuredin order to estimate from how many pieces the anchorswere fabricated and how many junctions were forged-welded.Anchor A was cut into pieces using a water-cooled steel disc.Eight metallographic cross-sections, A1–A1 up to A8–A8,were taken from the different zones of anchor A (Fig. 5) and

sections were prepared according to the ASTM E3-01. Thesample surfaces were ground with silicon carbide 240 to 600grit papers, then polished with alumina paste from5 to 0.05 μm,

and then polished with 0.05 μm colloidal silica suspensionpastes. To remove contaminants, the samples were cleanedwith ethanol and dried. Next, the samples were etchedwith Nital (97 mL ethyl alcohol and 3 mL nitric acid). Themetallographic samples were examined under an OM (ZEISS,AXIO-Scope A.1). Vickers microhardness tests were performedusing a Future-Tech Model FM-700e microhardness tester, witha load of 100-g force.

Fig. 7 – Radiograph image of the: (a) area in the anchor which was radiographed, (b) higher magnification of the radiograph revealing

the forge-weld line (arrows).

Fig. 8 – Anchor A cross-sections after cutting: (a) section A1–A1, (b) section A2–A2.

Table 1 – Analyses performed on each anchor.

Object Typology Radiography Cross-section SM OM SEM/EDS XRF OES Hardness

Anchor A + + A1–A1 + + − + − +A2–A2 + + + − − +A3–A3 + + − − − +A4–A4 + + + + + +A5–A5 + − − − − −A6–A6 + + − − − +A7–A7 + − − − − −A8–A8 + + + − − −

Anchor B + + − − − − − − −


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4. Results

4.1. Anchor A

The shank of anchor A had a round cross-section; its arms hadrectangular cross-sections and were almost perpendicular to the shank, as typical for T-shaped anchors [3,5,22]. Therewere visual indications over the surface of the anchor, suggestiveof forge-welding connections, such as shown in Fig. 6.

More than ten radiography tests were performed on anchor A revealing a suspectedforge-welding area that wasnot seen onthe surface (Fig. 7). The suspected area was characterized in theradiographs by a tilted inner planar surface, about 4.5 cm along theshank, starting about 5 cm from thearms.It should be notedthat the darker areas in the radiographs indicate absence of matter. Examination of the outer surface of the shank revealedno signs of an underlying weldment. It should be noted thatthe radiographs did not cover the entire anchor surfaces.Complementary sections were also made.

4.1.1. Section A1 – A1

OM observation of the metallographic samples of section A1–A1 (Figs. 5a, 8a) after etching revealed a heterogeneousmicrostructure of ferrite, pearlite and cementite network aswell as Widmanstätten plates (Fig. 9). Microhardness mea-surements on section A1–A1 revealed two areas with typicalaverage hardness values of 154±25 HV and 219±41 HV.The two areas were separated by a large cavity (Fig. 8a).

The carbon content was estimated from the measuredmicrohardness to be 0.2–0.6 wt.%.

XRF measurements were performed at two different pointson section A1–A1, as summarized in Table 2. The compositionwas found to be mostly Fe, 98.8–99.5 wt.%, with some other elements, including up to 0.1 wt.% Cr, up to 0.7 wt.% Al,0.1 wt.% P and between 0.3 and 0.4 wt.% Si (Table 2).


Macro examination of external surface of A2–A2 revealed afine line that might indicate the forge-weldment that wasseen in the radiographs. Examination of section A2–A2 after cutting it (Figs. 5a, 8b) revealed an inner cavity whose size,location and orientation agreed with the radiographs, indi-cating forge-welding. OM and SEM observation of the metal-lographic samples of section A2–A2 after etching revealed aheterogeneous microstructure of ferrite, pearlite, cementitenetwork and Widmanstätten plates (Fig. 10), as well as wüstite(FeO) slag inclusions. The measured microhardness wasbetween 85 HV, which is typical for pure iron, up to 248 HV,which is typical for pearlite, with average value of 123±70 HV.

Two areas were analyzed with SEM-EDS at a magnificationof ×50, as summarized in Table 3a. It was found that thecomposition was 95.9–97.3 wt.% Fe, 2.3–3.4 wt.% C and smallpercentages of Al, Si, P, S, Mn and As.

4.1.3. Section A3 –

A3

Observation of the metallographic samples of section A3–A3(Fig. 5a) with OM and SEM revealed a heterogeneous microstruc-ture of ferrite, pearlite, cementite, and Widmanstätten plates, aswell as slag of wüstite (FeO) and glass. The microhardness was

Fig. 9 – OM photograph of Widmanstatten plates (A1–A1

cross-section).

Table 2 – XRF analysis results from two measurement points.

Cross-section Compositions weight percentage (wt%)

Fe Cr Al P Si

A1–A1, Point 1 98.8 0.1 0.7 0.1 0.3A1–A1, Point 2 99.5 – – 0.1 0.4A4–A4, Point 1 100.0 – – – –

A4–

A4, Point 2 99.3 – –

0.1 0.6

Fig. 10 – OM photograph showing heterogeneous micro-

structure of cementite (center), pearlite (left) and

Widmanstätten plates (right).

Table 3a – SEM-EDS elemental analysis of the metal.


Fe C Al Si P Mn As O

A2–A2 (area 1) 95.9 3.4 0.2 0.1 – 0.1 0.3 –A2–A2 (area 2) 97.3 2.3 0.2 0.1 0.1 – – –

A4–

A4 98.5 0.8 –

0.3 –

0.1 –

0.3


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between 77 HV (typical for pure iron), up to 123 HV, which istypical for ferrite with some pearlite, with an average valueof 104±14 HV. The slag microhardness was 487–582 HV. Noevidence of forge-welding lines was identified in this section,specifically not between the arm and the fluke.


OM and SEM observation of metallographic samples of section A4–A4 (Fig. 5a) after etching revealed a heterogeneousmicrostructure of ferrite, pearlite, cementite and Widmanstättenplates, as well as a high level of slag inclusions such as wüstite,fayalite and glass. The microhardness was between 78 HV and169 HV(average hardness of99±25 HV), which istypicalfor ferritewith a small amount of pearlite. The slag hardness was 273 –493HV.

The composition of the metallic region, determined byEDS, was 98.5 wt.% Fe, 0.8 wt.% C and other elements (Si, Mn

and O), as summarized in Table 3a. The EDS composition of theof glassy slag (Fig. 11a) was 26.7 wt.%Fe, 19.7 wt.%Si, 4.1 wt.% Al,5.4 wt.% Ca and of 30.3 wt.% O, and smaller amounts of Mg, K,Mn, Mo, Ti (Table 3b). Three-phase slag, wüstite-fayalite-glass,and two-phase slag (wüstite-glass) in ferrite iron was also

observed by SEM-EDS (Fig. 11b, c, respectively). The two-phaseslag was composed of 43.2–79.9 wt.% Fe, 0.1–13.9 wt.% Si and of 17.4–29.8 wt.% O, and small amounts of Al, Mn and Ca (Table 3b).

XRF indicated an iron composition of 99.3–100.0 wt % Fe,with up to 0.1 wt.% P and up to 0.6 wt.% Si ( Table 2). OESindicated that the composition included Fe, C, Si, Ni, Mo, Tiand P (Table 4).


Macro-examination of section A5–A5 (Fig. 5a) revealed no signsof forge-welding. Therefore, this section was not examinedfurther.

Fig. 11 – SEM photos of: (a) a glassy slag inclusion, (b) three-phase (wüstite-fayalite-glass) slag inclusion surrounded by α-ferrite

grains, (c) and (d) two-phase slag (wüstite-glass) surrounded byα-ferrite grains.

Table 3b – SEM-EDS elemental analysis of the slag.

Cross-section Compositions weight percentage (wt.%)

Fe C Al Si P Mg K Mn O Ca Mo Ti

A4–A4Fig. 11a

26.7 9.2 4.1 19.7 – 1.7 1.3 1.0 30.3 5.4 0.4 0.2

A4–A4Fig. 11c point 1

79.9 1.0 0.3 0.1 – – – 1.1 17.4 0.1 – –


43.2 1.1 3.0 13.9 0.8 0.4 1.2 1.7 29.8 4.9 – –


79.2 1.1 0.3 0.2 – – – 0.8 18.4 – – –

A4–A4

Fig. 11c point 4

47.5 1.5 2.5 12.7 0.7 0.5 1.0 1.6 28.5 3.5 – –


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A6Macro examination of the external surface of A6–A6 (Fig. 5a)revealed two forge-welding lines (Fig. 12, white arrows). Obser-vation of the metallographic samples of section A6–A6 with OMafter etching revealed a heterogeneous microstructure of ferrite,pearlite, cementite network and Widmanstätten plates, as wellas transparent glassy slag, two-phase slag (wüstite-glass) inferrite iron and two-phase slag (fayalite laths in glass) in a ferritematrix (Fig. 13). Microhardness measurements made for the A6–A6 section revealed an average value of 153±39 HV, which istypical to a combinationof ferrite andpearlite. The slag hardnessvalues are between 544 and 673 HV.


A7The goal of examining section A7–A7 (Fig. 5a) was to determinewhether the observed external layer was a coating layer at theexternal part of the anchor or whether it an oxidation layer.SEM/EDX analysis of the external layer revealed only a highpercentage of O and Fe without any other elements, confirming that there is no outer layer or coating.


Macro examination of the external surface around the throat(the junction between the shank and the arms) revealedindications of forge-welding connection lines, as shown inFig 6. Metallographic examination of section A8–A8 (Fig. 5a)

after etching revealed clear and sharp borders between twodifferent microstructures (brighter and darker), one with ferritegrains and the other with pearlite grains, separated by a regionwith Widmanstätten structure.

The clear and sharp border suggests that two parts wereforge-welded together, each with a different microstructure.The tilted view in Fig 14 shows the connection between theindications of forge-welding lines on the external surface

and the metallurgical findings shown in Fig 15. The locationof this area, close to the throat also supports its being a forge-welding (Fig. 15a). The direction of the slag, shown in Fig. 15b,is parallel to the borderline, supporting the interpretation of aforge-welding line here.

OMandSEM-EDS examination andanalysis aroundandalong the borderline in the metallographic sample of section A8–A8

(Fig. 15b) after etching did not reveal strong evidence of slag, fluxusage or oxidation lines. The change in the microstructure at theforge-welding line was continuous and smooth, indicating highquality forge-welding in this area (Fig. 15).

4.2. Anchor B

As has been mentioned, anchor B was studied to a limitedextent in comparison to anchor A. Visual examination of anchor B revealed that its shank was round and its arms had arectangular cross-section and were almost perpendicular tothe shank, similar to anchor A (Fig. 4). There were visualindications on the surface of anchor B, including the throat,

suggesting forge-weldments, such as shown in Fig. 16.Only a few radiographs were made on parts of the surface of

anchor B. In the radiography photographs that were performedon anchor B, no evidence of forge-welding lines was seen,probably as a result of significantly greater corrosion damagethan in anchor A. The significant corrosion damage made itdifficult to distinguish between the deep surface corrosion andinner cavities that might be a result of imperfect forge-welding.

5. Discussion

Multidisciplinary typological and archaeometallurgical methodswere used to investigatethe manufacturing processes of thetwoanchors, focusing on anchor A. The purpose was to characterizethe composition, microstructure, forge-welding junctions andslag inclusions. Dozens of metallurgical cross sections werestudied in different locations and orientations.

The archaeometallurgical analysisof Anchor A indicatesthatit was made of wrought iron. It had a heterogeneousmulti-phasemicrostructureof ferrite, pearlite,cementiteand Widmanstättenplates, rich in slag (glassy slag, fayalite, wüstite), as typical of wrought iron. The parallel elongated wüstite slag indicates thatthe anchor was manufactured by hot working. Although silicaslag particles were found, there is no hard evidence that silica

was specifically used as a flux in the forge-welding areas.The metallographic investigation revealed that anchor A wasmanufactured without any additional heat treatments andfolding techniques, probably because of cost-effectivenessconsiderations. In the majority of the cross-sections, variablecarbon zones were observed, from low carbon zones (< 0.3 wt.%)to medium (0.3–0.6 wt.%) andhighcarbon zones (>0.6 wt.%). Thehardness of anchor A is similar to that of anchor B [3, p. 241] andmatches that of other working tools such as ancient wroughtiron saws, sickles, axes and mortise chisels [23].

From both radiographic and metallographic observation itwas seen that anchor A was of high quality, and manufacturedby expert blacksmiths. Only the combination of radiographs,

visual observation, OM and SEM/EDS observation and analysis

Table 4 – OES analysis (average of 3-points).


Fe C Si Ni Mo Ti P

A4–A4 99.85 0.09 0.01 0.01 0.01 0.01 0.02

Fig. 12 – Tilted view of section A6–A6 showing two dimensional

joining plain (arrows).




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of the metallographic sections made it possible to locate theforge-welds of anchor A and examine them. It was found thatthe ‘straight scarf weld’ method was used to join the anchor blooms. Each armof anchor A (the arm and the fluke) was madeof one 2–3 kg unit, while the shank was made from a few

1.5–

2 kg blooms (at least five blooms, Fig. 17). During the firstmanufacturing stage, the shank and the crown (lower part of the shank) round sections were manufactured and combined.The arms were manufactured separately, and shaped to their rectangular shaped cross-section with the flukes at the end of the arms. At the next stage, each arm was connected to theshank to form the final anchor.

The results from anchor B, although briefly studied, showthat each arm was made from two pieces, each piece weighing about 3 kg. The remaining piece of the shank weighs about7 kg and most probably was composed of at least two pieces,each one weighing 3–4 kg.

This assumption is based on the total weight and measure-ments of the arms and the shank remains and on the forgewelding location assumption according to the visual indicationsthat were observed over the surface of the anchor.

Beside iron and carbon, XRF, SEM-EDS and OES showed thepresence of Si, Al, Ti, Cr, Mn, As, P, Mo and Ni in anchor A iron,while SEM-EDS analysis of the slag revealed Fe, C, Al, Si, Mg, K,

Fig. 13 – OM photos of fayalite (Fe2SiO4 ) slag matrix: (a) surrounded by ferrite and pearlite, (b) high intensity of light revealing

the slag texture, (c) higher magnification of the ferrite and pearlite, and (d) higher magnification and high intensity of light, revealing

the slag texture.

Fig. 14 – Tilted view revealing evidence of forge-welding joint in section A8–A8.


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Mn, O, Ca, Mo and Ti. Comparing our results with the chemicalanalysis of the anchor from the Yassıada I shipwreck [14]indicated that most elements were detected in both anchors.

This study also corresponds to the metallurgical analysis of theiron anchors from Yassıada I that reveal the use of wrought ironwith similar microstructure and composition [14] to those of anchor A. In the Serçe Limanı shipwreck, the anchors werecomposed of several blooms, but the welding lines were notdetected during the metallurgical examination [10,15].

Good identification of the forge-welding locations mustcombine visual inspection, radiography and metallurgicalsections, together with some prediction and understanding where forge welding connections can be expected. This workshowed that each one of the inspection methods alone isnot enough to identify all the locations. The combination of non-destructive and destructive testing enabled us to reachgood understanding and enriched our knowledge in all that is

concerned with manufacturing processes of anchors made inthe local early Islamic period.

6. Conclusions

Among the finds excavated from the Tantura F shipwreck,two T-shaped type iron anchors were discovered, dated tobetween the mid-seventh and the end of the eighth centuriesCE.

Anchor A was made of wrought iron, with heterogeneousmicrostructure, manufactured by hot working and then itspieces were joined together by ‘straight scarf ’ forge-weld.Anchor B generally supports the results from anchor A,but being larger, its arms were made from two blooms each.Although the technology of making complicated structures,e.g., used in swords, using heat treatments and folding

Fig. 15 – (a) forge-weld joints in section A8–A8; (b) SEM image showing border between two different microstructures — ferrite

and pearlite, separated by a Widmanstätten microstructure zone.




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techniques, existed at that time, anchors did not requirethis sophistication and so simpler techniques were used,presumably because they were more cost-effective. The anchor

microstructure was similar to other simple ancient tools suchas saws, sickles, axes and mortise chisels.

Since the typology of the anchor studied here is similar toother anchors from the same period, our understanding of themanufacturing and forge-welding techniques may contribute tothe understanding of the manufacturing processes of those

anchors.

Acknowledgments

This research was supported by the Israel Science Foundation,the Hecht Foundation, Lord Jacobs of London, a Sir MauriceHatter Fellowship for Maritime Studies and the University of Haifa, to whom the authors are thankful.

We gratefullythank Izhak Hershko andDanBrightman fromthe radiography department of the SOREQ Nuclear ResearchCentre, for their outstanding and constructive help.

Many thanks go in particular to Shirly Druker, DemitryFishman, Igal Galper, Ofer Levi, Ulia Naim, Gil Shemesh,Efrat Shwartzberg and Din Wilson.

R E F E R E N C E S

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[3] Eliyahu E, Barkai O, Goren Y, Eliaz N, Kahanov Y, Ashkenazi D.The iron anchors from the Tantura F shipwreck: typologicaland metallurgical analyses. J Archaeol Sci 2011;38(2):233–45.

Fig. 16 – Anchor B: (a) photograph suggesting forge-weld joints (arrows), (b) 3-D illustration schematic showing the different parts

of the anchor (top view).

Fig. 17 – Forge-welding lines revealed in Anchor A ( — ) and

suggested reconstructed forge-welding lines ( − − − ).


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