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Chapter 2.2 Laser Cleaning of Stone Artefacts Johann Nimmrichter,
Robert Linke
Federal Office for Care and Protection of
Monuments
in Austria, Department for Conservation (Bundesdenkmalamt), Arsenal
Objekt 15, Tor 4, 1030 Vienna, Austria Contents 2.2.1
The Beginning Chapter 2.2 PowerPoint Presentation (8.9 MB) Since the early 1970s, laser technology has been successfully applied for cleaning of artefacts. The first cleaning treatment with a laser was done on stone works in Venice/Italy by an interdisci¬plinary team coordinated by J. Asmus in 1972 [1]. A ruby holographic laser was modified and used for cleaning the lion portal at Palazzo Ducale in Venice and other objects of art made of marble. Although the cleaning results were convincing, for a longer time laser was only used rarely. In a few cases C. Calcagno applied the laser technology for cleaning sculptures or ornaments made in bright marble or limestone. Up to the middle of the 1980s the interest for this technique increased in Europe. In France, Italy, Greece, Germany, and Great Britain interesting cleaning projects with laser tools were started. Basic research was done in order to improve the laser tools and to test it on a wide range of applica¬tions. Because of these efforts the laser tools became easier to handle and today they are suitable for work on scaffolding. From this moment the possibilities for cleaning have not focused only on stone materials. Laser cleaning technologies were also tested on metals, wood, ceramics, ivory, paintings, textiles and many other inorganic and organic
materials.
The responsible institutions in the field of
care and protection of monuments and artworks are very careful and
critical with new conservation techniques and so a lot of preliminary
examinations and tests were carried out by scientists and
conservator-restorers. In the field of stone conservation the laser
cleaning technique is usually compared with other traditional
techniques (e.g. micro sand-blasting, paper pulp pad impregnated with
an aqueous solution of ammonium carbonate and ion exchange resins) [2].
In many cases laser cleaning showed advantages and therefore some very
interesting conservation projects could be carried out with Nd:YAG
lasers (e.g. Romanesque portal of Cremona, the portals of the Cathedral
of Amiens [3] or Notre Dame in Paris). Especially on very delicate
surfaces with thin scaling or brittle parts the laser offers the better
alternative cleaning method. However, problems have been observed in
connection with some pigments and some binding media. In some cases the
yellowing of the stone surfaces after laser treatment represents an
aesthetical problem.
At the present there is a concentration on
Nd:YAG lasers for stone conservation, although other types of lasers
(see also chapter 1.1) could also be successfully applied in special
cases.
2.2.4
Principles of Laser Cleaning and Its Application The process of laser cleaning is described
extensively in Chapter 2.1
and can be explained in a simplified way by evaporation (photo thermal
ablation mechanism) and ablation/spallation (photo mechanical and photo
chemical ablation mechanism) effects. As shown in the transparency no.
4 of the ppt-presentation, the intensity of absorption or reflection of
the laser light, which is (mainly) caused by the soothed substrates
(stone, dirt, layers of over paint etc.), is mainly responsible for the
quality of cleaning. In the simplest case a bright white stone is
covered by a black dark crust. After the evaporation/ablation of the
black crust there is no dark material absorbing the laser light and the
laser will be reflected without producing any damage for the white
stone. However, in reality such clear simple cases are rare and
difficult situations are making the process of laser cleaning quite
complex. Table 2.2.1: Comparison of different methods of cleaning at the Romanesque West portal of St. Stephen’s Cathedral in Vienna/Austria.
It is also very important for the conservator-restorer to follow safety regulations thoroughly. Protection with special glasses for the eye, gas-mask, appropriate cloths, exhauster and a right isolation with a sign for danger of the working place (studio, scaffolding, workshop) where the laser is used are an absolute mandatory (slide no. 11 in the PowerPoint presentation).
2.2.5.1
Introduction,
Principles 1) Laser cleaning
of stone artefacts. 2) John the
Baptist from Donatello (Venice, Frari church). 1972 John Asmus, Lorenzo
Lazzarini and M. Marchesini made holographic images. Beside, they
started to clean pieces of art made in marble with a ruby laser. From
the first moment on the results were promising. Unfortunately, the
beam repetition (repetition frequency) was very slow. 3) In the 1980ies
one of the first big laser projects has been carried out. A part of the
Romanesque portal of the cathedral of Cremona was cleaned with a
Nd:YAG laser (normal mode 1064 nm) by John Asmus and Giancarlo
Calcagno. The laser was a prototype and it was difficult to handle it
on the scaffolding. The stone was a compact limestone. The evaluation
after 20 years showed very good results. 4) Description of
the laser activity during the cleaning process by John Asmus (In:
Martin Cooper, Laser Cleaning in Conservation. Butterworth Heinemann,
Oxford 1998). 5) Important
parameters for the laser tool – see also text. 6) Parameters and
requirements of monuments and artworks made in stone: 7) Cleaning
samples and scientific controlling: R. Sobott and others made a lot of
tests on German sandstones. The tests are made with different pulse
energy, photo: R. Sobott, published by H. Seidel, K. Neumeister, R.
Sobott: Anwendungsbeispiele an Denkmalobjekten, In:
Laserstrahlreinigung von Naturstein, Stuttgart 2002, p. 89. 8) Weathering
profiles of limestone before and after cleaning: On the left side of
the slide there are two scanning electron micrographs of
partial cleaned surfaces (photo: M. Cooper: Laser Cleaning in
Conservation, Butterworth Heinemann, Oxford 1998, p. 69. 9) Comparison of
different cleaning systems by Verges-Belmin. 10) This
comparison of cleaning techniques was made by G. Calcagno in Padua.
“A” was cleaned with an ammoniumcarbonate pad,
“L” was cleaned by laser and
“M” treated with micro-sand-blasting. After
cleaning all epitaphs were treated with silan/siloxane. 11) Protective
measurements/laser safety:
2.2.5.2
Case Study: St. Stephens Cathedral in Vienna 12) Many areas
and objects were cleaned with laser e.g. the main entrance (Westportal)
and a lot of ornamented and figurative parts. (photo: J. Nimmrichter). 13) St. Stephens
Cathedral in Vienna: frieze (1340) at the north facade from the chorus,
before and after laser cleaning (photos: J. Nimmrichter). 14) Chorus of St.
Stephens Cathedral in Vienna (1998-2004): pre-cleaning was done by
micro sandblasting. All fine parts (sculptures, windows, ornaments)
were done by different types of lasers (Palladio, Michelangelo,
Laserplast, Thaleslaser). (photo: E. Pummer). 15) St. Stephens
Cathedral in Vienna, Gothic relief: Calcareous sandstone with
polychrome traces; water spraying accelerates the laser cleaning. The
brownish colour was caused by the historic oil impregnations. At the
detail the advantage of the laser is visible. Only by laser this
scaling parts could be conserved. (photos: E. Pummer, J. Nimmrichter). 16) The Gothic
relief and two Renaissance epitaphs after laser cleaning and
conservation (photo: J. Nimmrichter). 17) St. Stephens
Cathedral, West Portal: Before and after cleaning (photo: J.
Nimmrichter). 18) St. Stephens
Cathedral, West Portal: Scientific analysis and a perfect documentation
of painted surfaces is the condition for a responsible laser cleaning
of polychrome layers. In a photogrammetric map all positions of
analyses are fixed. All observations of colours are documented.
(photos: J. Nimmrichter). 19) St. Stephens
Cathedral, West Portal: By means of scientific investigations (optical
and scanning electronic microscopy) the reconstruction of the
Romanesque, Gothic, Renaissance and Baroque polychromy was possible and
necessary for the following laser cleaning. (photos: J. Nimmrichter). 20) St. Stephens
Cathedral, West Portal: In connection with the polychrome surfaces
tests with these pigments were started, e.g. azurite or Naples yellow.
Partly the small fields of colour were covered by a layer of soot and
dust. Afterwards, laser cleaning with different laser energies was
carried out. (photos: J. Nimmrichter). 21) St. Stephens
Cathedral, West Portal: Effects of Nd:YAG laser on three pigments with
different aged binding media (wax, mastic gum, casein) were analysed.
(photo: J. Nimmrichter). 22) St. Stephens
Cathedral, West Portal: More tests have been carried out for having
exact dates. The first line of photos shows four analysed
cross-sections, the second line the localisation and the third line the
test field. With 400, 500 and 600 mJ the surface was treated 1, 4 and 8
times with the laser. (photos: J. Nimmrichter and H. Paschinger). 23) St. Stephens
Cathedral, West Portal: Documentation of the parts, where laser
cleaning was done. For controlling also reflectance spectroscopy was
carried out. (photo: J. Nimmrichter and G. Calcagno). 24) St. Stephens
Cathedral, West Portal: Comparison of the working times of the
different cleaning methods. Only in combination with all these cleaning
techniques a good and successful conservation of the West Portal could
be achieved. 25) St. Stephens
Cathedral, West Portal: Evaluation after 9 years; there were no
problems with the water uptake, colour change, new soiling at the
consolidated stones and colour traces. (photo: J. Nimmrichter). 26) St. Stephens
Cathedral in Vienna: the grave of “Neithard Fuchs”.
The grave sculpture was made in calcareous sandstone (from Au). Traces
of only one Gothic paint layer, which was painted directly onto the
stone, were found. The architectural parts were made in red lime-stone
(like Verona red). Both kinds of stones could be cleaned by laser.
(photos: J. Nimmrichter). 27) St. Stephens
Cathedral in Vienna: The grave of “Neithard Fuchs”.
The facade behind the grave was painted with ochre, grey lime washes
and dark joints. This surface was cleaned by laser and ammoniumcarbonte
compresses. On the right the Gothic painting is reconstructed and an
old documentation of the sculpture is compared with the new one.
(photos: J. Nimmrichter).
2.2.5.3
Further Case Studies
in Austria 28) Renaissance
epitaph from the Chapel St. Margaret in Steyr in Upper Austria: Laser
cleaning was done on Austrian red lime stone, so called
“Adneter red” (same type as “Verona
red” or “Hungarian red”, a calcareous
sandstone with traces of azurite layers). On all surfaces the results
have been successful. No changes of the azurite and no darkening or
yellowing at the stone material itself could be observed. (photos: J.
Nimmrichter). 29) The small
scaffolding was covered with a safety awning. The microscopic images
show the red stone and azurite layer before and after laser treatment
(photos: J. Nimmrichter, R. Linke). 30) Gothic Church
from Bad Deutschaltenburg in Lower Austria: Cleaning was done with
micro sandblasting and Nd:YAG laser. (photo: E. Pummer). 31) Four Gothic
portals of the Minoriten Church in Vienna. Calcareous sandstone with a
thin old lime layer. Analytical proofed with optical and scanning
electron microscopy. (photos: E. Pummer, H. Paschinger and J.
Nimmrichter). 32) Minoriten
Church in Vienna: West facade with the three portals and the half
cleaned north portal. (photos: J. Nimmrichter). 33) Houses of
Parliament in Vienna: 19th century building, sculptures from the
“Attica” are made of Carrara and Laaser marble.
(photos: J. Nimmrichter). 34) Portrait
stone of a Roman grave from the archaeological collection of the castle
in Eggenberg near Graz, Styria: Cleaning of a mixture of black crusts
and vegetative attack; the microscopic images show the successful
cleaning of a coarse-grained local marble. (photos: J. Nimmrichter, H.
Paschinger). 35) Laser
cleaning of stucco from a “Jugendstil-facade” in
Vienna (around 1900). 36) Allegory of
sculpture from v. Tilgner from around 1900, Carrara marble: Laser
cleaning on crystalline marble; very low ultra sonic speed showed a
very bad condition of the marble. After a pre-consolidation the
transport could be carried out only in a polyurethane form and the
laser cleaning was in this case the most sensible way to remove the
black crusts. (photos: J. Nimmrichter). The soft yellowing was treated
with paper compresses.
37) The cleaning
of the Parthenon West Frieze with ultraviolet and infrared laser
radiation: Because of this combination a yellowing was avoided. (K.
Frantzikinaki, G. Marakis, A. Panou, C. Vasiliadis, E.
Papakonstantinou, P. Pouli, Th. Ditsa, V. Zafiropulos, C. Fotakis,
YSMA/FORTH). On the left side the modified laser tool can be seen, on
the right side a half cleaned relief. 38) Church of
Maddalen in Venice: Istrian limestone, before and after laser cleaning.
(work was done by E. Pummer and G. Calcagno). 39) Example of
laser cleaning in France and Portugal: Gothic Cathedral of Nantes,
where laser was used for the sculptured west portal. The cross yard of
the monastery of San Geronimo in Lisbon. (photos: J. Nimmrichter). 40) Sienna, brick
facade of the City Hall: Parts of the bricks and traces of polychrome
layers (malachite, azurite and iron-oxide-red) were cleaned
successfully with a Nd:YAG laser. (photos: E. Pummer and J.
Nimmrichter). 41) Laser types
used for stone cleaning: Homepage of COST G7, collected by M. Cooper.
[1] Lazzarini, L., Asmus, J., Marchesini, M.: Lasers for the cleaning of statuary, initial results and potentialities. 1st Intern. Symp. on the Deterioration of Building Stones, La Rochelle, 1972, 89-94. [2] Asmus, J.: Serendipity, punctuated. Proceedings of LACONA VI, Vienna 2005, in print, Springer-Verlag, Heidelberg, 2006. [3] Vergés-Belmin, V.: Comparison of three cleaning methods – micro sandblasting, chemical pads and Q-switched YAG Laser - on a portal of the cathedral Notre- Dame in Paris. LACONA I, 1997, 17-24. [4] Weeks, C.: The conservation of the Portal de la Mere Dieu, Amiens Cathedral, France. LACONA I, 1997, 25-29. [5] Pouli, V., Frantzikinaki, K., Papakonstantinou, E., Zafiropulos, V., Fotakis, C.: Pollution encrustation removal by means of combined UV and IR laser radiation: The application of this innovative methodology on the surface of the Parthenon West Frieze, LACONA V, 2003, 143-149. [6] Cooper, M.: Laser Cleaning in Conservation, Butterworth Heinemann, Oxford 1998, 65. [7] Calcagno, G., Koller, M., Nimmrichter, J.: Laser based cleaning on stonework at St. Stephens Cathedral, Vienna. LACONA I, 1997, 39-43.
2.2.6.2 Literature on Laser Cleaning of Stone Artefacts LACONA I, Heraklion, Greece: Restauratorenblätter Sonderband, Lasers in the Conservation of Artworks, Eds.: M. Koller and R. Brandstätten, Verlag Mayer&Comp, Vienna 1997. LACONA III, Florence, Italy: Journal of Cultural Heritage, Lasers in the Conservation of Artworks, Eds.: R. Salimbeni and G. Bonsanti, Elsevier 2000. LACONA IV, Paris, France: Journal of Cultural Heritage, Lasers in the Conservation of Artworks, Ed.: V. Vergès- Belmin, Elsevier 2003. LACONA V, Osnabrück, Germany: Lasers in the Conservation of Artworks, Eds.: K. Dickmann, C. Fotakis, J.F. Asmus, Springer Proceedings in Physics, Springer Verlag, Berlin-Heidelberg 2005. LACONA VI, Vienna, Austria: Lasers in the Conservation of Artworks. Eds.: J. Nimmrichter, M. Schreiner, W. Kautek, Springer Proceedings in Physics, Springer Verlag, Berlin-Heidelberg 2006. Cooper, M.: Laser Cleaning in Conservation. Butterworth Heinemann Oxford, 1998. Wiedemann, G.: Laserabtragung dünner Deckschichten. Eine alternative Reinigungsmethode für die Restaurierung und Denkmalpflege - Möglichkeiten und Grenzen. Fraunhofer-Institut Dresden, Germany, 2000. Seidel, H., Wiedemann, G.: Laserstrahlreinigung von Naturstein. Fraunhofer IRB Verlag, Stuttgart 2002. Lasertechnik in der Restaurierung. RESTAURO 10 (1998) Callwey Verlag, München 1998.
www.lynton.co.uk/conservation.asp www.ekspla.com/en?eksma_entrance=1 www.lambdascientifica.com/ita/codice/indexrestauro.php www.elengroup.com www.cohr.com www.quantron.com www.alpha1.infim.ro/cost/ www.alpha1.infim.ro/cost/pagini/Lasersummary.xls www.cleanlaser.de www.boomsystem.pl/index/?id=43ec517d68b6edd3015b3edc9a11367b www.riegl.com www.atelier-pummer.at
Department for Conservation (Bundesdenkmalamt) Arsenal Objekt 15, Tor 4 1030 Vienna Austria E: arsenal@bda.at E: johann.nimmrichter@chello.at E: linke@gmx.at http://www.bda.at/ |
