Conveyed by optical fibre, a beam of light wipes away the imprint
of time. Designed for cleaning buildings, in particular monuments
to our cultural heritage, the LAMA laser allows the buildings to be
freshened up without causing any harm to the material. This innovative
tool, which is efficient, manageable, ergonomic and quiet, does not
involve the use of water or sand and makes it possible to reach areas
inaccessible by other methods.
Using the Lama laser to clean one of the
statues of the Hôtel de Ville, Brussels
Four minuscule dots of light act like a magic
eraser, and the sculpture changes rapidly from a dark to a light colour.
The persistent beam brings details to life. Certain parts remain greyish,
revealing a history of earlier botched restorations. In Deinze (Belgium),
in a workshop belonging to the small MRT company, all the statues
of Brussels' Hôtel de Ville, which forms the heart of its illustrious
Grand'Place, have been brought along to benefit from this soft facelift.
In Italy, the restorers Trivella have tested the LAMA handheld laser
and compared it with other methods - such as microscale sandblasting
or chemical pulps - on a number of pilot sites including Milan Cathedral,
the Strozzi Palace and Lucca Cathedral. In France, following the renovation
of the Hôtel Godin (Tours), a demonstration was organised at the Galliera
Museum (Paris) in the presence of various parties responsible for
historic monuments, who will eventually decide, on a case-by-case
basis, whether to make use of this technology.
None of these methods is completely satisfactory. As Jean Weiss, Technical
Director of the GTM Group, points out: "To attack the stonework in
the course of the cleaning process is frequently tantamount to attacking
its protective layer, which is the epidermis of the stone and which
keeps alive our memory of the original work down the ages. In reality,
such an operation increases susceptibility to subsequent pollution
and, consequently, shortens the life of the material."
The effect of light beams on stains has been known since the early
1970s, and various teams of researchers (in Italy, the United Kingdom
and France) have carried out studies on the possibility of applying
this technology to the restoration of the cultural heritage. Professionals
from this sector, such as the specialists of the Jaulard company,
a subsidiary of GTM Construction (France), are rapidly becoming
aware of the attractions of this method. In their opinion, the "hard"
techniques (pressurised water, sandblasting, hydro-sandblasting),
frequently used because of their low cost (15
/m2), show scant regard for materials and the environment. They
are also aware that the soft techniques (spraying, microscale sandblasting,
chemical processes), while offering higher performance, nevertheless
entail such high financial outlays (450
- 1500 /m2) that they are employed solely in the case of particularly
valuable objects. But intermediate solutions , such as "erasing",
which vary in cost from 30
/m2 to 75 /m2,
Palazzo Ruffo (Rome). Graffiti, test and
Laser to measure
Under a project supported by the Brite-EuRam programme and implemented
between 1993 and 1996, eight European partners got together to develop
an effective, less expensive, soft technology.
The first stages of the research on the use of laser beams were
devoted to an analysis of the "material-stains" pair. "These two
elements are inseparable," Jean Weiss goes on, "since what we are
trying to do is to eradicate the ravages of time without degrading
the work itself. Each of these two materials is characterised by
a light energy density "threshold" above which an ablation effect
is produced." Fortunately, in the majority of cases, the threshold
of the stain is less than the threshold of the material, and the
density of the energy used will inevitably fall between these two
Altogether, 71 pilot sites across Europe, with 126 different "material-stain"
pairs, were chosen. About a hundred samples of stone (limestone,
marble, granite, etc.) stained by plants, urban pollution, traces
of paint, etc. were meticulously analysed in terms of density, water
absorption, type of stain, etc. They were then subjected to cleaning
tests using various methods, ranging from the gentlest, such as
atomised water and microscale dry sandblasting, to the most aggressive
such as hydro-sandblasting and high-pressure washing, as well as
laser beams. Very often the laser beams come out on top: no damage
to the material, no abrasion effect, no excessive discoloration,
no denaturing of the texture, etc. "A number of laser parameter
combinations - wavelength, energy density, pulse duration, etc.
- have been tried out, and it is on this basis that two prototypes
were designed," explains Adolfo Pasetti of the Centro Studi Trivella.
Optical fibre, flexible beam
"The research effort was to be geared towards increasing the average
power of the sources and looking into possibilities for standardising
the distribution of energy over the impact surface," Jean Weiss
explains. "This is why the research and development effort has focused
on the possibility of using optical fibres as a means of conveying
the radiation, rather than delivering the beams by means of mirrors.
This option enhances quality - by avoiding the risk of excessive
cleaning at the centre, at the expense of the periphery. It increases
the rapidity of cleaning very significantly by increasing the utilisation
rate of the projected energy, i.e. the useful energy. It also ensures
a high degree of equipment manoeuvrability and better ergonomics."
The LAMA is available in the form of a particularly functional
"kit". On the ground, there is the laser and its cooling unit (two
small cube-shaped machines which can also be placed on scaffolding);
the operator has a handheld instrument weighing about 1 kg, comparable
to a light camera; positioned between the two there is a cable between
10 and 12 metres long to protect the optical fibres. (This has not
prevented a demonstration, in the Lebanon, on stelae situated at
the top of a cliff, where cleaning was carried out from a cage positioned
at a height of 70 metres using suitably extended fibres).
Offering equivalent quality to that of the soft technologies, this
promising tool, manufactured by Quantel, provides lower-cost high-efficiency
performance (1m2 per hour, on average). Other applications employing
this technology could be introduced in the industrial sector (e.g.
mould cleaning in the glass and plastics industry) and - precisely
because the radiation is conveyed by optical fibres - in the more
specialised area of nuclear decontamination.
Meanwhile, in 1997 pending these potential developments, the ALTRAN
Foundation for Innovation (France) awarded the LAMA its new technology
prize "for services to the collective memory of man and the human