CIRAM - Scientific Tests on Works of Art - 2013

AUTHENTICATION EXPERTISE

DATING

Works of Art

Europe - Phone +33 5 56 23 45 35 – Mobile +33 6 64 14 24 10 - [email protected] North America – Mobile +1 917 509 5616 - [email protected]

© 2012 - www.ciram-art.com



When Science meets Arts

More than a Simple Provider, CIRAM promises to be a Quality Scientific Partner

and an Experienced Adviser.

Over the past 10 years, CIRAM Scientific Team have analyzed more than 5,000 objects for the Most Renowned Dealers, the most Prestigious Auction Houses

and Major National Museums.

Extract of the commercial references of CIRAM Art Dealers: Jacques Barrère, Brimo de Laroussilhe, Pierre Dartevelle, Bernard De Grunne, Christian Deydier, Bernard Dulon, Lance Entwistle, Sam Fogg, Fortuna, Michael C. Hughes, Guy Ladrière, J.J Lally & Co, Nasser & Co, Pace Gallery, Phoenix Ancient Art, Royal Athena, Simon Ray, Jules Speelman Auction houses: Artcurial, Christie's, Koller, Piasa, Pierre Bergé & Associés, Sotheby's, Tajan Museums: Louvre, Petit Palais, Auguste Rodin, Arthur Rimbaud, Fondation Giacometti, The American Battle Monuments Commission

Study of Authenticity on stone, bronze, brass, silver,

gold, glass, painting…

Dating with C14 and TL tests on wood, ivory, textiles, terracotta…



Study of Wood, Ivory, Bone, Textile

Radiocarbon (C14) Dating

Scientific analysis of objects made of wood, ivory, bone and textiles (canvas for example) is based on the dating of the raw constitutive material of the pieces, using Carbon 14 method. The age obtained gives information about the death of the organism. Assuming that the C14 measurement does not concern the shaping itself, we can, nevertheless, determine if the antiquity of the material (its date) is consistent or not with the presumed period of the object and identify forgeries and restoration areas. An X-ray exploration of the objects can give further information about the shaping of the pieces and their structural homogeneity. 1

st step: Dating of the Raw Material – Invasive (50 to 200 mg)

Carbon 14 dating is based on the measurement of the amount of the

14C that

all organic materials contain (wood, plants, bone, ivory, …). It permits to determine the time since the death of the organism (tree was cut down, cotton was picked, death of the animal,...). R

adio

carb

on a

ge [B

P]

Calendar date [AD]

Calibrated date 1170 – 1264 AD (95.4 %)

The accuracy of the dating depends on the antiquity of the material.

It can vary between 100 years for

material older than 300 years,

and 250-300 years for younger ones (from 17

th to 1950 AD), because of the

necessary calibration of the C14 ages.

Radio

carb

on a

ge [B

P]

Calendar date [AD]



2

nd step: Object Homogeneity – Non intrusive

For material younger than 1950 AD, we can obtain a very accurate date (less than 10 years), considering the effects of the atmospheric nuclear bomb tests.

The X-Ray exploration allows to observe the structural homogeneity of the object and identify:

Restoration areas (R)

Assemblies of ancient (A) and modern (M) materials

C 1

4 m

easure

ment

[F C

14]

Calendar date [AD]

Calibrated date 1962 – 1963 AD ( 6.0%) 1976 – 1977 AD (89.4%)

Calibrated date 1669 – 1710 AD (15.9%) 1716 – 1780 AD (26.7%) 1797 – 1890 AD (36.7%) 1909 – 1944 AD (16.1%)

Radio

carb

on a

ge [B

P]

Calendar date [AD]

In the range 1650 AD – 1950 AD, we have several possible intervals of calibrated dates for one radiocarbon age. Nevertheless, we can promote one or two of them regarding the percent of probability that affects each interval.

M

A

R



Sample n° 0411-OA-14M-1-P2

TL as a function of irradiation dose

-5,10

500

1000

1500

2000

2500

3000

3500

-8 -6 -4 -2 0 2 4 6 8 10

TL intensities between 290 -370 °C ED value (Gy)

Dose (Gy)

ED value

TL Intensity (a.u.)


TL as a function of irradiation dose

-0,60

500

1000

1500

2000

2500

3000

-2 0 2 4 6 8 10

TL intensities between 290 -370 °C ED value (Gy)

Dose (Gy)

ED

value

TL Intensity (a.u.)


Thermoluminescence curves

0

500

1000

1500

2000

2500

3000

3500

4000

50 100 150 200 250 300 350 400 450

Nat

Nat + 4,4 Gy

Nat + 8,8 Gy

Background

TL Intensity (a.u.)

Temperature (°C)


Thermoluminescence curves

0

500

1000

1500

2000

2500

3000

3500

4000

4500

50 100 150 200 250 300 350 400 450

Nat

Nat + 4,4 Gy

Nat + 8,8 Gy

Background

TL Intensity (a.u.)

Temperature (°C)

Terracotta Analysis

Thermoluminescence (TL) Tests For more than 30 years, the authentication of terracotta is based on thermoluminescence (TL) analysis, which gives an estimated age of the last heating of the material, with a standard deviation typically around ± 20%. Nowadays, in order to detect more sophisticated forgeries, it is often necessary to complete the thermoluminescence approach with the visualisation of the internal structure of the object, with X-ray radiography or scanner. Crossing these two scientific techniques, in association with a stylistic analysis, guarantees the authenticity of a terracotta object. 1

st step: Thermoluminescence Test - Intrusive

( 2 mm drilling)

TL curves and antiquity evaluation obtained on this sample show that it was heated a long time ago. The estimated age should be about 1000 ± 150 years old.

For a recently heated object, TL curves (red) exhibit low intensities. Then, antiquity evaluation gives a recent age.



2

nd step: Object Homogeneity – Non intrusive

If the thermoluminescence analyses reveal a recent material, then the object is probably a forgery.

If the results indicate it is an ancient material,

we suggest completing the analysis with X-Ray radiography or scanner, in order to evaluate the homogeneity of the object.

X-Ray imaging of this horse shows it is composed by numerous terracotta pieces assembled with a modern technique. Even if TL showed the antiquity of the material, the observation of its structure indicates that this horse is modern.

X-Ray radiography of this figure shows no internal anomalies. Associated with TL results, it allows us to confirm its antiquity.



Stone Study

Sandstone, Limestone, Schist, Jade, Marble Dating a stone is possible, but it concerns the creation of the material, and not the carved phase. So, we have to analyze the corrosion processes of the stone. As they are very slow, the study of stone figures is efficient for objects presumed to be at least 300 years old. As a consequence, our analysis require complementary approaches (tools marks, surface deposits, weathering of stone, origin of this corrosion…) that form a body of evidence, from which we can discuss about their chronological compatibility with the presumed period of the carving of the object. 1

st step: Surface Analysis – Non intrusive

This preliminary study allows us to exhibit modern treatments or not, but it is not sufficient to establish the antiquity of an object. We can investigate for:

Traces of carving and polishing, tools chips

Superficial deposits: burial sediments, modern application

Surface treatments: cleaning, acid treatment

Ancient and modern polychromy

lithopone white

(1870 AD)

Modern polishing marks (arrows)

Manganese-rich deposits (M) voluntary applied

M

M

Modern polychromy on a modern object or an ancient one



2nd

step: Material and its Corrosion - Intrusive

(5 x 5 mm)

According to the nature of the stone, the corrosion processes expand differently, but we have to observe a weathering gradient between the carved face and the inside part of the stone. The natural corrosion of a stone presents different features:

Surface Porosity Grains Decohesion

Differential Dissolution

Desquamation of the Surface

Reprecipitation of iron and manganese oxides

Gradient of Weathering

An artificial corrosion of the stone can be made with strong acids (hydrochloric, sulfuric, phosphoric, hydrofluoric ...). They leave detectable elements (Cl, S, P, F) and a homogeneous weathering frontline.

Important decohesion of grains (arrows) at the carved surface (C)

Decohesion of grains (arrows) at a broken area (B). Medium level.

C

B

No decohesion or other corrosion features inside the stone

Fluorine-rich

layer

The expand of corrosion (arrows) is sub-parallel to the surface



Study of Metal Alloys

Bronze, Brass, Iron For copper alloys (bronze and brass), we look for long time processes. So, in the most cases, we only analyze objects presumed to be at least 300 years old. The composition of the alloy, the nature and the degree of the corrosion establish a body of evidence, which indicates if these results are consistent or not with the presumed period of the object. If the piece has a closed shape and contains a residual casting core, a thermoluminescence test can be performed as a complementary approach with the metal analyses. 1

st step: Alloy Composition - Intrusive

(< 1mm)

The first step of the analysis is to define the composition of the alloy and the nature of the embedded inclusions. We can detect formal elements of modernity, such as aluminium or phosphorus. We can exhibit the incompatibility of the composition of the alloy with the presumed date of the object (zinc-aluminium-

copper-lead alloy, for example).

Even if the composition is not inconsistent with the presumed date of the object, it cannot be considered as a

fundamental proof of authenticity.

Aluminium indicates this brass has been made after 1850 AD.

Zinc-aluminium alloys do not

correspond to antique techniques.

Is this "classical" bronze ancient or modern?



2

nd step: Corrosion Study - Intrusive

(2 x 2 mm)

3rd

step: Object Homogeneity – Non intrusive

We have to observe if the corrosion expands deep inside the alloy (natural origin) or if it remains superficial (artificial origin). We also have to define its physical/chemical features:

Inter-granular Corrosion

Trans-granular Corrosion

Weathering of lead globules and their shift to the Surface

Superficial increase of tin associated with the preferential Corrosion of copper-rich phase

Dezincification for Brass

Composition of Corrosion products (the "patina") and Research of Chemical attack evidences (chlorine, sulfur).

The X-Ray investigation of the object allows us to observe the structural homogeneity of the object and to identify: Restoration areas,

Assemblies of ancient (A) and modern (M) alloys

Corrosion processes (arrows)

expand inside the alloy.

Typical dendritic corrosion (arrows).

Corrosion processes (arrows) are superficial.

They result from an acid treatment.

A

M



Study and Dating of Gold & Silver

For gold and silver objects, the corrosion processes are very slow. We need more accurate information. This is possible by coupling scanning electron microscope and external beam PIXE or ICP/MS (Mass Spectrometer) investigations. 1

st step: Superficial deposits

The first step is to define the origin of superficial deposits, from their composition. Is it a natural and burial deposit, which is composed by silicated mineral phases (clay), lime phases and metal corrosion products? or is it an artificial deposit? On gold objects, we commonly detect brown orange deposits, which correspond to ferric chloride. It results from an acid attack used to simulate corrosion and burial deposits. 2

nd step: Trace elements composition

The second level is to define the accurate composition of the alloy and especially its trace elements composition (less than 0,1%). Indeed, the ancient extraction techniques produced metal with many impurities. That is why ancient gold and silver contain many typical trace elements. The trace composition is obtained with external beam PIXE (non destructive analyses) or with ICP/MS. 3

rd step : Corrosion study

The last level is performed to observe the superficial micro-corrosion of the alloy. This allows us to eliminate forgeries made from ancient gold or silver. The natural corrosion of gold object induces such features as a smooth and irregular texture, some numerous pits and an inter-granular corrosion. The corrosion of silver corresponds to the embrittlement of the alloy. The U,Th -

4He dating method for gold objects

The concentration of helium is proportional to the age of manufacturing. When gold crystals are formed in the earth, uranium (U), thorium (Th) and many other trace elements are incorporated into the crystal. When U, Th decay to lead (Pb), they also emit an helium atom (

4He)

which remains embedded in gold. So, 4He concentration increases with time.

To manufacture a gold object, we have to extract gold from the ore. The melting process induces the evaporation of

4He, but not U, Th. This constitutes our zero time, when

4He concentration is null. So,

when the goldsmith achieves the object, the gold alloy still contains U, Th, but not helium. The radioactive decay of U, Th continues and the "production" of helium restarts. By determining the concentrations of U, Th and

4He, we can estimate the age of the object.



Study of Rock crystal The rock crystal (quartz) is a very resistant material which does not alter. Thus, we propose two alternative nondestructive techniques which collect information about the surface state and the age of the carving phase. Tools marks investigation To study the surface of an object, we use, a CIRAM exclusive none-destructive technique, the “Surface Impression”. It gives a fingerprint of the surface with the additional interest of sampling the invisible surface deposits. Surface Impression gives information such as the tools marks and the chemical composition of superficial compounds. So, we can detect the type (modern or ancient) of the used tools, and the traces of eventual surface treatments such as acid treatment. The surface investigations are not sufficient to establish the antiquity of an object. Quartz Hydration Dating (QHD) If the tools marks investigation did not give a relevant clue or if we want to proceed with complementary research, we use the Quartz Hydration Dating (QHD) which is based on the gradual penetration of the water in the crystal. This technique is very useful for Rock crystal, Glass, Chalcedony, etc… It relies on the phenomenon of water diffusion into the lattice leading to the formation of a hydration layer. It can be measured by a hydrogen profiling technique using a 2.2 MeV ion beam from a particle accelerator.

The more hydrogen detected at a deeper level, the older the object is.

In comparison with a modern piece of chalcedony (black and red curves), an old object (blue curves) shows a higher and deeper concentration of hydrogen. The depth of penetration of the hydrogen atoms is evidence of antiquity.

0

25

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200 300 400 500 600 700 800 900 1000

Canaux

Nb

re d

e co

up

s d

étec

tés

Echantillon (surface)

Calcédoine récente (surface)

Calcédoine récente (cœur)



Study of Paintings The scientific analysis of a painting answers various questions:

- Characterization of the painting techniques, - Statement of restoration/preservation of the works of art, - Authentication research

The results obtained complement stylistic expertise. The analysis produces objective data essential to the knowledge of the work of art such as:

- research of a signature, - observation of underlying drawings, - visualization of pentiments, - identification of restorations, - characterization of the different materials used, - dating of the support (canvas, wood, paper,…)

We synthesize our study in a fully documented report, combining all the photographic documentation and the analysis results. Dating the support We date by radiocarbon (C14) the support (canvas, wood, paper…) and eventually the frame. This information is essential to establish the possible age of the painting. A canvas made in the 20

th century cannot be the support of a 19

th century work.

Search of Chemical composition We use Scanning Electron Microscopy (SEM), Raman, FTIR and PIXE, to characterize the chemical composition of the pigments, of the extenders, of the binders and of the painting grounds. From those results, we can check if the materials are consistent or not with the presumed period. These analyse are very relevant for the 19

th and 20

th centuries paintings.

Xray pictures

The X-Rays penetrate all the layers of painting and the support. It permits to obtain an image of the distribution of the materials according to their density. X-ray radiography allows to appreciate the preservation state of the work of art showing restoration areas. Besides, it constitutes an efficient tool to characterize the presence of pentiments and surpaints.



To learn more about CIRAM Services To ask for a Study

Visit our website www.ciram-art.com

Contact us EUROPE Office & Laboratory, Bordeaux, France

Phone / Fax +33 (0)5 56 23 45 35 e-mail [email protected]

NORTH AMERICA Office, New York, USA

Mobile +1 917 509 5616 e-mail [email protected]

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CIRAM - Scientific Tests on Works of Art - 2013

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