CIRAM Authentication Of Stone Objects - 2013

www.ciram-art.com 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]

Stone Study Sandstone, Limestone, Schist, Jade, Marble

Version 1.3 updated June 18thi 2013

www.ciram-art.com

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]

The characteristics of the stone THE MATERIAL ITS WEATHERING

It is an heterogeneous material that associates mineral phases more or less denses, more or less resistant… Sandstone: sedimentary stone composed by quartz, feldspars, micas aggregated by a clay or calcitic cement. Limestone, marble: stones composed by calcite and dolomite. Granite, Schist, … Jade, Stone crystal, …

Q Q N

K

K

M

C

C

sheeding, weathering, erosion

Embrittlement of the surface

Ionic exchanges, dissolution, reprecipitation

Area weathered In surface


www.ciram-art.com


The characteristics of a stone

Why does the composition of the stone constitute the first step of the analysis? We investigate the weathering processes of the stone. They directly depend on its nature:

⇒ reprecipitation of iron and/or manganese oxides on the sandstones ⇒ disintegration and dissolution of the calcite in limestones ⇒ …

Some modern materials are used to simulate stones.

Sorel cement (magnesium oxychlorides)

invented in 1867


www.ciram-art.com


The surface analysis THE TOOLS’ SHAPING MARKS ü traces of shaping of the stone, by bush hammering… ü decor by incisions ü …

⇒ Recently sculpted ⇒ Recently cleaned up

⇒ Formerly sculpted ⇒ Recently sculpted with a metal of "ancient type"

THE TOOLS’ POLISHING MARKS We use an abrasive (hard mineral) of small-size. The result is the presence of polishing scratches.

Acier inoxydable (Fe-Cr-Ni) stainless steel

Iron

METALLIC SHREDS

Ancient alloy: iron, bronze…

Modern alloy: Stainless steel, tungsten…

Traditional techniques (manual) leave scratches with variable and

multidirectional dimensions.

Modern techniques (mechanical) leave fine and unidirectional

scratches.


www.ciram-art.com


The surface analysis THE SUPERFICIAL DEPOSITS They are generally constituted of earth, roots, fungus, … These deposits can come from a natural environment (burial sediments) or from a voluntary application.

Fungus and/or bacteria colonies: buried in a humic environment

Iron and Manganese mineral silicated phase : natural deposit or pigment applied ?

Clinker phase: modern cement Volontary application, to simulate roots’ traces


www.ciram-art.com


The surface analysis THE DECORATIONS It is generally about polychromy or lacquer.

THE SURFACE ANALYSIS, in summary:

Ø Preliminary study that permits to turn down the obvious fakes.

Ø Complementary to the analysis of a cross-section, to characterize the whole object.

Ø Study necessary, but not sufficient to establish the antiquity of an object.

White lead (ceruse)

White titanium (1923)

Pigments and techniques are of

modern type

Pigments and techniques are of ancient type

⇒ Original polychromy

⇒ Modern polychromy realised with pigments of ancient type

⇒ Application moderne sur un objet ancien

Modern application on a modern object

Modern application on an ancient

object

Lithopone white(1870)

Ferric chloride: orange acid used to attack the material and to simulate a burying deposit. Absolutely not, a cleaning product or a natural compound.


www.ciram-art.com


Deteriorated stone Undeteriorated stone

Deteriorated stone Undeteriorated stone

Stones weathering THE CHARACTERISTICS OF THE WEATHERING –The superficial porosity A superficial porosity, caused by the cement dissolution, is developing. It is a natural phenomenon, nevertheless it is necessary to control there is no acid residue.

THE CHARACTERISTICS OF THE WEATHERING – The superficial decohesion The grains present in surface break away the ones from the others. This is also caused by the partial dissolution of the cement. It is nevertheless necessary to control the decohesion does not come from the work of manufacturing.


www.ciram-art.com


Stones weathering THE CHARACTERISTICS OF THE WEATHERING – The differential dissolution The feldspars are more sensible to deterioration than quartz. That’s why we have to observe the preferential dissolution of the feldspars. We also observe the exfoliation of the micas. In calcareous stones, we find this phenomenon of preferential dissolution of calcite than dolomite.

Deteriorated stone

Q

F

Undeteriorated stone

Q F

F

Undeteriorated stone

M

Deteriorated stone

Q

M


www.ciram-art.com


Stones weathering THE CHARACTERISTICS OF THE WEATHERING – The desquamation The desquamation surface is the extreme result of the decohesion and of the dissolution. It can be observed as well on sandstones as on limestones.

THE CHARACTERISTICS OF THE WEATHERING – The reprecipitation of oxides The dissolution of the intergranular cement and the exchange with the environment involve the formation of oxides and/or of hydroxides of iron and of manganese: "black patina" of the sandstones.


www.ciram-art.com


Stones weathering THE CHARACTERISTICS OF THE WEATHERING – The gradient The carved surface has to show deterioration degree more important than in the middle (cutting line) or than at the level of the breaks. The intern part of the stone and the break areas are better preserved, since they suffer few or no direct "attacks" from the environment. It results a deterioration gradient between the carved surface, the breaks areas and the interior of the material. THE CHARACTERISTICS OF THE WEATHERING, in summary:

Ø The superficial porosity

Ø The superficial decohesion

Ø The differential dissolution

Ø The desquamation of the surface

Ø The reprecipitation of iron and manganese oxides

Ø Presence of a weathering gradient

Is it necessary to observe all this criteria to claim a stone is naturally deteriorated?

Is it possible to reproduce artificially these processes?

Surface sculpted Break Cutting line

Stone gradually weathered


www.ciram-art.com


Stones weathering THE ARTIFICIAL WEATHERING The only means to accelerate or simulate a deterioration, is to make a surface treatment, principally with strong acids: hydrochloric, sulphuric, phosphoric, hydrofluoric acid...

⇒ Elements markers of this type of attack Cl, S, P, F ⇒ There is no differential dissolution ⇒ The front attack is linear

In summary… The authentication research uses a bundle of clues that permits to define:

Ø The nature of the material Ø The degree of the weathering Ø The deterioration gradient Ø The nature of the decay

The surface analysis permits to obtain complementary information:

Ø The tool marks Ø The superficial deposits Ø The decoration

Nevertheless these analysis techniques encounter limits:

Ø They are not dating techniques. Ø They study slow processes: efficient for objects of at least 300 years old. Ø The samplings are reduced compared to the dimensions of the object. It would be necessary to

define, in complement, the degree of homogeneity and deterioration of the object.

Fluorine (HF acid)

Fluorine (HF acid)

Stone artificially deteriorated


www.ciram-art.com


The homogeneity degree of the object The X-ray radiography This method allows to evaluate the structural homogeneity of the piece and to locate:

⇒ the restoration areas ⇒ the assembly areas

However, the dimensions often important of stone sculptures limit our investigations by X-ray radiography (penetration of the X-rays).

No break in the neck Break in the neck

Break in the neck and metallic tenon


www.ciram-art.com


In summary…

The authentication research involves the complementarity of the approaches and of the analysis methods:

Analysis of the constitutive material of the object

Analysis of the degree and the nature of the weathering

Characterization of the intern structure and of the homogeneity of the object

CIRAM proposes a wide range of analysis permitting to bring the information necessary, to rigorous search of authentication.


www.ciram-art.com


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]

Join us Facebook, Linkedln, Twitter, Issuu, Slideshare, Pearltrees

CIRAM Authentication Of Stone Objects - 2013

Technology

Transcript of CIRAM Authentication Of Stone Objects - 2013