Lasers Cleaning of Patrimonial Plasters

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Lasers Cleaning of Patrimonial Plasters

Eric Tanguy, Nathalie Huet, Armand Vincotte

To cite this version:

Eric Tanguy, Nathalie Huet, Armand Vincotte. Lasers Cleaning of Patrimonial Plasters. Lasers in

the Conservation of Artworks (LACONA V), Dec 2004, Osnabrück, Germany. pp.125-132,

�10.1007/3-540-27176-7_15�. �hal-00935184�

l

of t

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u-ger and Richard W.

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.

Sartiani, A. deCruz, ombini,"The Er:YAGlaser.An ntings: testing and evaluation," ll-14, (2001) 121-124

.d M. Rizzi, "A novelapproach ting materials by Er:YAGlaser ier, Paris (2003)

'he Role ofLasers in Fine Arts :WS, 10 (1999) 36-40

sr, "Laser removalofcontam

i-LiHeritage, supplement 1-2000,

rbioper la pulitura deidipinti: e-Decembre(2001)55-61 ics & chemistry ofsurface abla

-IV, "Lasersintheconservation '-120

Lasers Cleaning of Patrimonial Plasters

E.

Tang

u

y", N.

Hu

et+, and A.

Vi

nço

t

te''

1 University of Nantes,LPIO,Facultédes Scienceset Techniques, 2, ruedela Houssinière,44000Nantes, France

eric.tanguy@physique.univ-nantes.fr

2 Arc'Antique, 26,rue de laHaute Forêt, 44300 Nantes, France

arc.antique@wanadoo.fr

Abstract. The use of the lasers Q-switched Nd:YAG to removethe dust of the

stone monuments especially sculpture gradually replaces the more abrasivetech -nique of sandblasting.This tendencymadeus considerthelasers as solution for the

cleaning ofceramics and theplasters.Indeedinmuseums,thesematerials areoften coveredwith dirty mark (dust, grease, etc.) whichisdifficult to remove without

damaging the object. Thispaper deals withthe impact of different types of lasers

(Nd:YAG first and third harmonic)irradiation on plaster andwith the effects on

itsmorphologyand its crystallography. Plasteris an interesting materialbecause of

itstypicalacicular crystals altered at low temperature. That is whysynthesis sam

-pleswereprepared, constrained in temperature then analysed byvariousprocesses

(SEM,XRD,TGA... ). Theseresultswerecomparedwithsamplescleaned bylaser.

That enabled usto concludethat plasters cleaned byUV-laser (third harmonicof

the Nd:YAG) underwent neither yellowing,nor morphologicalorcrystallographic changes.It hasto beopposed to theintenseyellowing,andsometimesmorpholog

-icaldestruction,which appears with an infraredwavelength (first harmonic ofthe

Nd:YAG).

1 Introduction

N

um

e

rou

s

plaste

r

s

are

f

o

und i

n m

u

se

um

s

(

o

rigin

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l

sc

ul

p

tur

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e c

op

ies

o

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s

impl

e cas

t

s

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. P

l

as

ter

e

nd

s t

o get dirt

y

v

e

r

y

qui

c

kl

y wha

t i

s

due to it

s

min

e

r

a

logic

a

l

a

nd ph

ys

ic

a

l characteri

s

tic

s

(di

e

l

ect

ri

c

con

s

t

a

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t .

.

.

).

Be

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u

se

of i

ts

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at

ur

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l fr

a

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nd

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ensitivit

y

to moi

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ure and physi

ca

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far

sto

n

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1

]

,

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.

2

Choi

ce

of the Wa

ve

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Th

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fir

st tests ha

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ni

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an

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use of the third harmonic

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harmonic, (b) 2nd harmonic,

give out a too white surface

,cleaning, The

yellowingob-Glaser [2

,

3] is reversible by

'ithout apparent damage for

ird

h

a

rmoni

c

of the Nd:YAG

Jut that neither

morpholog-'. Therefore

,

we made some

rtworks and the dirty marks

the results obtained in this

r of the Molda 3 typ

e,

typi-1

1%) and mixed the powder

rmmon that the sculptor

s

or

tion of milk to improve

tex-tal moulds of approximately

,

causing any tran

s

formation

to the face in contact with

this kind of surface are less

in contact with the mould

,

l'hus

,

the possible effects of

l

damage on surface will be

LasersCleaning of Patrimonial Plasters 127

Fig. 2. Crystal morphologyof the faceincontact with the air

Fig. 3. Deposit of carbon graphit

A natural dust contamination would be too long and

insufficientlyrepro-ducibl

e

. We thus chose a deposit of carbon graphite reduced to powder

a

nd

applied to the brush (Fig

.

3)

.

This powder forms part of porosities and makes

it possible to obtain a fine and homogeneouslayer.

4 Treatment

in Temperature

Laser ablation induced a fast but localizedrise in tempe

r

ature in the medium.

However the modifications of phase of the plaster occur for temperatures

ranging between lOODCand 1200DCFig. 4

.

Plaster is an interesting

mate-rial because of its typical acicular crystals (CaS04

.

2H20

P)

altered at low

temperature (120DC

=

CaS0

4

.0,5H20

P) [4].

In order to detect possible

mod-ifications of phases of the plaster cleaned by laser

,

samples were fir

s

t th

e

r-mally treated

,

at various temperatures

,

then they were observed with th

e

SEM and, eventually th

e

y were reduced to powder and analysed by x-rays

diffraction (Fig. 5). Th

e

s

e

data will be employed as references and will b

e

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LasersCleaning of Patrimonial Plasters 129 .lpha 800 crstcam _G 200e essure ~,5H201 -;;-600 _G C-o

e

~ 400 G hydrate ),:H2

o

l

~

G .'ê200 lriteIII ₀ L..._ ;' 10 20 30 40 50 2thêta (degré) on of the temperature 500 H H roc-e 400 A A C- H

:la

g300 A

~

_H ~ 200 A =

~)

.~ 100 H G A

.k

o1\'",",,'

,

10 20 30 40 50 2thêta (degré) transformation of the sample 2 thêta (degré) 400.---~ 3000e H H ";;'300 g-o ~200 :£ ~ 100 the fundamental wavelength thod of cleaning by the third

o was dirtied and cleaned on

son (Fig.

6)

.

The energy used

2)

and 90mJ (0.72 Jjcm2) at

10 20 30 40 50

Fig. 5. Modificationofthe plaster phases versustemperature at 20, 100 and 3000C

(DRX - SEM),G: gypsum, H: hemihydrate, A: anhydrite

nples treated in temperature

ig. 7

by UV does not undergo any

l. Moreover, this method of

laser shows clearly that the

lour. On the other hand, it is

e fundamental wavelength of

dification of its surface, that

the influence of the heat on

Referenceplaster

Carboned plaster to be cleared

Fig. 6. Samplebeforecleaning

mated at O.16Jjcm2 for the

hold ofthe plaster isaround

Hn~ ém ' znojoc aqt laqt~aU say n latS'BId aqt JOllu ~ U'Bap aqj, IU~t 'BOJ at~qM. aEll'B1Jaqt uaAa I aqt JOarruorua s auy aqt pUTI paU'Bap ÂpJa pad al'BsaJ'B Jms ' paapuI ' StInSal ÂlOp'BJSq'BSqt~ M. (; wJ /

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n

a

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s

form

e

d on

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e s

urf

a

ce of

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Lasers CleaningofPatrimonial Plasters 131

Fig. 9. plasma formed on the surface

Uncleaned area

Uncleaned area

a b

Fig. 10. Pieta partially cleaned byUVlaser

and th

e

fine

s

tructur

e

of the moulding or th

e s

urfac

e

qu

a

li

ty

is still p

res

erv

e

d

,

e

ven

t

h

e

f

ra

gil

e w

hi

te c

oa

t

ing

.

6 Conclusion

Th

e

cl

ea

nin

g

of th

e

pl

as

t

e

r u

s

ing

t

h

e

third h

a

rmonic of

N

d

:

YAGl

aser m

o

di

-fie

s

n

e

ither the co

l

our

,

neithe

r

th

e c

ryst

a

llo

-

graphi

c

s

t

ructur

e

nor

t

h

e

pha

se

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