The secrets of the Anglo-Saxon gold-smiths Hoa… · Secrets of the Anglo-Saxon Goldsmith: The...

Secrets of the Anglo-Saxon Goldsmith:

The results from the analysis of the gold in the Staffordshire Hoard

Dr Eleanor Blakelock

Staffordshire Hoard

• Found in 2009 by a metal detectorist

• Near the village of Hammerwich, near

Lichfield, in Staffordshire.

• Excavation by archaeologists from

Staffordshire County Council, and a team

from Birmingham Archaeology, which was

funded by English Heritage.

• When the discovery was publicly announced,

it attracted worldwide attention with people

queuing for hours to see the hoard.

Staffordshire Hoard

• Over 3,500 objects or object fragments have

been found, predominately gold or silver.

• The Hoard is essentially military in character.

The bulk of the identified pieces comes from

the handles of edged weapons, shield fittings

and one or more helmets.

Anglo-Saxon Warrior Elite

“The great Anglo-Saxon poem Beowulf, once

believed to be artistic exaggeration, now has a

true mirror in archaeology.”

Chris Fern

Staffordshire Hoard

But ……… there are a few other objects of unknown use

And a small number of explicitly Christian items have also

been identified

It is still likely that these were taken from a battlefield, as

it was not uncommon to take your priest to war

Staffordshire Hoard

• The Hoard was valued at £3.285 million

• An international fundraising campaign to save the hoard for the nation was mounted

• In less than 10 weeks it was a success

• It is now jointly owned by Birmingham and Stoke-on-Trent City councils.

• The collection is displayed in four museums

Staffordshire Hoard

Research Project

• Metals analysis just one part of a larger study ....Contextualising Metal Detected Discoveries:

Staffordshire Anglo-Saxon Hoard

Conservation

Reconstruction

Typology

• Chris Fern the archaeologist is trying to create a typology to date the Hoard using stylistic information

• Also looking at status of individuals

Typology

c.620AD

c.625AD

c. 610AD

c. 560AD

c. 630ADc. 600AD

Identifying objects

Mystery Object

• No idea what it is, no parallels anywhere

• Is it the lid of a container?

• Saddle fitting?

• Or an extension to a hat?

Identifying objects

• This is a manuscript showing the prophet Ezra and he is wearing something on his head

Analysis• Gold

• Silver

• Copper alloys

• Gilding

• Garnet

• Glass

• Niello inlay

• Green inlay

• Organic

Research Project

• Metals analysis just one part of a larger study ....Contextualising Metal Detected Discoveries:

Staffordshire Anglo-Saxon Hoard

– Conservation & public engagement– Typology and classification of objects– Scientific analysis of materials

• Gold & silver• Organics• Pastes and glass

– Fully illustrated publication– Online research database

Gold Research Project

• Provenance the gold

• Can the gold be used to date the hoard

• Identifying workshops

• Choice of alloy for specific roles

• Effects of burial environment on gold

158 objects analysed

o 114 Staffordshire Hoard

o 1 Stoke on Trent

o 43 British Museum

• During the analysis 288 different components were analysed

o Sheets

o Filigree panels

o Cast or solid

o Wires

o Cell walls

o Large borders

o Caps

Choice of instrument

• Cheap and quick

• Museum owned one

• Completely non-destructive

• Large beam size

• Relatively deep penetration

SEM-EDX

• Small beam size

• Limited by object size

• Small penetration so surface had to be prepared

Surface

Anglo-Saxon gold

• Gold in the past was not pure

– Native gold contains silver and some copper

• Deliberate alloying of gold was also used to change the properties of gold

– Working properties

– Melting temperatures

– Colour

Anglo-Saxon gold100% gold

more silver

90% gold 10% silver

80% gold 20% silver

more copper

• This graph shows the range of gold alloys in the Staffordshire Hoard objects analysed

• Majority of objects have between 1-4% copper

70% gold 30% silver

Anglo-Saxon gold

• During the Saxon period there was a gold shortage

• Studies of coinage has shown a general change in the gold to silver ratios

• It was hoped that this information could be used to date the Staffordshire Hoard objects

0.0 20.0 40.0 60.0 80.0 100.0Si

Gold Wt%

c.630-640

c.630-660

c.650-675

c.670-680

Silver increases over time

Anglo-Saxon gold

• No clear pattern was seen relating to dates

• The Hoard will have to be dated based on stylistic differences

Anglo-Saxon gold

• Are there regional differences to perhaps indicate workshops?

• The analysis showed no clear regional groups

• Exception was Suffolk

Anglo-Saxon gold

• There was no obvious link between function and alloy either

Anglo-Saxon gold

• Evidence points to recycling and mixing

40 60 80 100

Weight% Au

0 2 4 6

Weight% Cu

Surface Enrichment Project

• Gold is resistant to corrosion but ..

.....the surface can be depleted of base elements, either naturally or deliberately

• In the burial environment

– Copper is depleted

– Small quantities of silver could also be potentially lost

Small quantities of silver lost at surface

Gold core composition K1143

83.7% gold, 14.3% silver and 2% copper

85.3% gold, 13.6% silver and 1.1% copper

Copper lost at surface

Gold enriched surface

• The term ‘surface enrichment’ is used but the surface has technically not been enriched in gold

• A pilot study was carried out on 16 objects to investigate the effects of the burial environment

Small quantities of silver lost at surface

83.7% gold, 14.3% silver and 2% copper

85.3% gold, 13.6% silver and 1.1% copper

Copper lost at surface

• Surface enrichment due to burial

• Hilt-plate K1143

• A small loss of silver at the surface.

• A substantial loss of copper due to the burial environment

75 80 85 90

Weight % Au

Surface

Sub-surface

0 1 2 3

Weight % Cu

surface

subsurface

Copper lost at surface Silver lost at surface

70% gold, 28% silver and 2% copper

84% gold, 15% silver and 1% copper

• Surface enrichment seen during pilot study

– A large number of objects had a significant loss of silver at the surface

– Some objects had over 40% depletion of silver

– Could not be explained by natural mechanisms

Sub-surface Surface

Sub-surface

Surface

60 70 80 90

Weight % Au

Surface

Sub-surface

0 1 2 3 4

Weight % Cu

• Surface enrichment seen during pilot study

The importance of the pilot study was recognised, so the surface enrichment project was extended.

This aimed to investigate differences in enrichment between

• Time periods

• Find location

• Components, to learn more about object construction and goldsmith workshops

• Function (including Male vs Female objects)

• The results suggested that only specific components on each object were being enriched

-30% -20% -10% 0% 10% 20%

% loss/gain of Au

Backing sheet

Cell Wall

All the components appear to have a similar core composition

Surface Enrichment Case study - K88

40.0 50.0 60.0 70.0 80.0

Weight % Au

Base sheet sub-surface

Top of cap sub-surface

Large filigree wire on panel sub-surface

0.0 1.0 2.0 3.0 4.0 5.0

Weight % Cu

Analysis showed that the sheet was depleted in silver

Sub-surface

Surface

Sub-surface Surface

40.0 50.0 60.0 70.0 80.0

Weight % Au

Base sheet surface

Base sheet sub-surface

0.0 1.0 2.0 3.0 4.0 5.0

Weight % Cu

Sub-surface Surface

Analysis showed that the sheet was depleted in silver

But the cap and wires show no sign of deliberate treatment

40.0 50.0 60.0 70.0 80.0

Weight % Au

Base sheet surfaceBase sheet sub-surfaceTop of cap surfaceTop of cap sub-surfaceLarge filigree wire on panel surfaceLarge filigree wire on panel sub-surface

0.0 1.0 2.0 3.0 4.0 5.0

Weight % Cu

Sub-surface Surface

Sub-surface

Surface

This may explain the colour contrast often seen between wires and the sheets behind them

It also suggests that the treatment was most likely taking place in the workshop

• Analysis was undertaken on sheets from different types of decorated object

o Filigree

o Cloisonné

o Cloisonné and filigree

o Green cloisonné

o Niello

o As cast or engraved objects

• The level of enrichment is different, based on the decoration method

• Sheets are more often enriched

obehind filigree

oengraved designs or plain sheets

• This suggests a deliberate choice by the goldsmith

• No difference in type or amount of enrichment based on object

– Date

– Location

– Function

the exception being ...

Male vs Female items -50%

-100% -50% 0% 50% 100%

Au weight%

Sword fitting

Items of personal adornment (female)

Items of personal adornment (male)

Religious function

-100% -80% -60% -40% -20% 0% 20% 40% 60% 80% 100%

Ag Enrichment Factor %

c. AD520-550

c. AD580-610

c. AD600-630

c. AD620-660

-100% -50% 0% 50% 100%

Ag Enrichment Factor %

Staffordshire

Cumberland

Buckinghamshire

Lincolnshire

Norfolk

North Yorkshire

Northamptonshire

Suffolk

• Part of the reason for including the British Museum collection was to get representative female items

Female vsMale

• More of the male associated items tend to have a higher gold core

• Instead the female items are more often enriched than male items

• This means that they tend to have the same surface compositions

50.0 60.0 70.0 80.0 90.0 100.0

Au Wt%

Decorative item (female)

Decorative item (male)

-0.40 -0.30 -0.20 -0.10 0.00 0.10

% loss/gain of Au

50.0 60.0 70.0 80.0 90.0 100.0

Au Wt%

Surface

Sub-surface

New Research at Birmingham

• Carried out in conjunction with Birmingham University

• SEM-EDX and metallographic analysis of a small number of objects

• Aim to determine

– the type of solders used

– how the surface was enriched

Solder

.5 1213

.5 1516

.5 1819

.5 2122

.5 2425

.5 2728

.5 3031

.5 3334

.5 3637

.5 3940

.5 4243

.5 4546

.5 4849

.5 5152

.5 5455

.5 5758

.5 6061

Solder

‘1 ounce of copper calcine, 3 solidus of olive-oil soap, 1 solidus of calcothar. For use mix these together first grinding the copper calcine and the calcothar separately into powder. Mix with as

much soap and water as is necessary for gold solder.’Mappae Clavicula circa 9th century AD Italy

So how did the Goldsmiths do it?Historical Sources Liquid or cementation bath Other

Kauṭilῑya Arthaśāstra Coat sample with Indus soil and heated

Agatharchides’s ‘On the Erythraean Sea’Lead, salt and tin, added to barley bran and placed in

vessel, heated

Pliny the Elder ‘Natural History’Gold heated with twice weight salt and three times

copper pyrites within earthenware jar

Leyden (or Leiden) Papyri

• Cementation of gold using misy, alum, salt coat gold

sheets but this is for purification as the gold is

melted

• Coloration of gold using misy, salt and vinegar in a

vessel which is heated

• 1 part gold and 2 parts lead powdered, coat and

heat object (for gilding copper objects)

• Yellow natron and salt, rubbed to gild

• Missy, alum and celandine in urine used to coat

sample heat applied to colour gold

Codex Lucensis 490Tragacanth, salt and vinegar used on gold textile

threads

Late Longobardian Latin document at

LuccaDragant and vinegar to colour gold threads

Mappae Clavicula

• Sinopia 1 part and 2 parts salt coat sheet and seal

with potters clay

• Paste of vitriol and salt, coat gold with it and heat

Greek manuscript ‘ On the noble and

illustrious art of the goldsmith’

• Salt, tartar dregs, third brick dust place in crucible

with gold, but this is for purification as the gold is

melted

• Suphur, garlic, urine and salt place sheet into

mixture

Oche and salt-ammoniac mixture to give golden

colour

Theophilus ‘ On Divers Arts’Salt, clay, urine in vessel with gold and heated, but this

is for purification as the gold is meltedSpanish gold with basilisk powder

Agricola ‘De Re Metallica’ Many recipes for the parting of gold by cementation

Benvenuto Cellini ‘Goldsmithing and

sculpture’Royal cement using tartar and brick dust to purify

Salt-petre, vitriol, salt and verdigris recipe applied

over the surface with a feather to colour gold

Vannoccio Biringuccio ‘treatise on metals

and metallurgy’Salt, brick dust with or without vitriol

• Verdigris and salt rubbed and heated

• Washed in boiled powdered yellow sulphur

So how did the Goldsmiths do it?

10.5 12

13.5 15

16.5 18

19.5 21

22.5 24

25.5 27

28.5 30

vessel, heated

melted

threads

Mappae Clavicula

with potters clay

melted

mixture

colour

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75

Sulphur

vessel, heated

melted

threads

Mappae Clavicula

with potters clay P

melted

mixture

colour

• Leyden Papyrus ‘roasted misy, 3 parts; lamellose alum, (and) celandine, about 1

part; grind to the consistency of honey with the urine of a small child and colour the object; heat and immerse in cold water.’

‘For gilding a vase of silver or copper without leaves [of gold], dissolve some yellow natron and some salt in water, rub it with this and it will be gilded.’

• Codex Lucensis ‘take clean tragacanth and carefully pound it in a mortar and

salt in equal weights, and rub, mix with diluted vinegar, spread over the petals on both sides equally with the first; and heat on the hearth to a moderate degree.’

• Mappae Clavicula ‘Take vitriol and roast it, as you know how, and as much salt

again, and temper it with red wine not too thinly, in a copper pot, and coat the gold with it.’

Life of an object

• There are many pieces in the hoard that look like they belong as sets

• Therefore a couple of obvious sets were examined during this study

• This revealed more about their life history

Market Rasen Staffordshire Hoard

Seax set

Au Ag Cu

72.4 25.3 2.2

85.0 13.9 1.1

82.2 15.2 2.6

82.0 15.3 2.6

82.2 15.5 2.3

65.0 70.0 75.0 80.0 85.0 90.0

Weight % Au

K376 sub-surface

K354 sub-surface

K690 sub-surface

K370 sub-surface

K449 sub-surface

• The hilt collars all shared a similar core composition

• But the pommel cap has a different composition

• This suggests that the pommel was constructed at a different time to the rest of the set

Market Rasen set

• The sheet of the pommel is made from a similar alloy as the cap, but has been treated

84 85 86 87 88 89 90

Au Wt%

Pommel sheet surface

Pommel sheet sub-surface

Pommel cap surface

Pommel cap sub-surface

Market Rasen set

• The sheets used in the pommel and both hilt collars are a similar composition

• The hilt plates however have different compositions

Au Ag Cu

85.3 12.8 1.9

75.2 21.6 3.2

83.6 13.8 2.7

84.7 13.4 1.9

77.2 20.4 2.4

Market Rasen set

• The bottom hilt plate has been treated to achieve a similar surface composition

• The top hilt plate hasn’t and is therefore a different colour

70 75 80 85 90

Weight % Au

Pommel sheet surfacePommel sheet sub-surfaceTop hilt plate surfaceTop hilt plate sub-surfaceTop collar surfaceTop collar sub-surfaceBottom collar surfaceBottom collar sub-surfaceBottom hilt plate surfaceBottom hilt plate sub-surface

Conclusion

• We know very little about the Anglo-Saxon goldsmith who made these pieces

• Deliberate surface treatment in the Anglo-Saxon period

• The data is beginning to reveal the

• methods and techniques used by the goldsmiths

• some of the thought processes and decisions made by the goldsmiths

For access to equipment

For funding the research

And the thousands of members of the public who donated towards the acquisition of the Staffordshire Hoard and who continue to support this campaign.

Was English Heritage

The Historical Metallurgy Society provides a

form for exchange of information and research in

historical metallurgy , and the conservation of all

historical and archaeological metallurgy heritage.

Activities:

• Conferences and special interest meetings

• Publish two Historical Metallurgy journal

volumes per year

•Updates via our newsletter The Crucible

Resources:

•Datasheets and guidelines

•Network of specialists

• Grants for research and travel

• Archives and reference collections

The secrets of the Anglo-Saxon gold-smiths Hoa… · Secrets of the Anglo-Saxon Goldsmith: The...

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