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Subject: Marble plaque

Marble plaque

From: Meg Abraham <mabraham>
Date: Monday, December 4, 2000
Paolo Recanati <consob [at] imj__org__il> writes

>I'm a conservator at the Object Conservation Department at the
>Israel Museum in Jerusalem and I would like to present some
>questions regarding the cleaning and consolidation a broken marble
>plaque (120 x 205 cm). ...
> ...
>    2.  Cleaning by laser gun: I saw it in operation in another
>        place in Israel and was wondering if it safe for only the
>        operator to use safety glasses or should other people
>        watching the process be wearing the safety glasses as well?
>        Also, what exactly happens to the dirt which is vaporized? I
>        was wondering if the vaporized molecules are safe to be
>        bouncing around and not be "collected" somehow. Is it safe
>        to breath this air?

Some weeks ago a question was asked regarding laser eye safety as
well as what happens to the vaporized material coming off the
artwork during laser cleaning.  The short answer is that laser beams
are generally collimated and so without a lens in front of them they
can damage the eyes of someone many feet away just as easily as to
those near by.  Most lasers used in conservation have a lens on the
beam delivery system which renders the light less dangerous at a
distance.  Still, before relying on that it is very important to
understand the physics of the laser light interaction with the eye
and the engineering design of the laser beam delivery system.  The
safest thing to do is to enclose the work space and require all
people inside the enclosure to wear appropriate eye protection.   A
very good source of information on this is the Laser Institute of
America.  They have small inexpensive books on the subject.

Regarding the material coming off of the art during cleaning.  It
does not just disappear but is usually volatilized into the
surrounding air.  The degree of health risk depends on what you are
ablating, but as a rule it is best not to breath the stuff.  Proper
ventilation, extraction trunks, and respirators are all good ways to
avoid inhalation of materials generated during laser cleaning just
as they are useful when using traditional methods of cleaning.

                  Conservation DistList Instance 14:32
                Distributed: Thursday, December 7, 2000
                       Message Id: cdl-14-32-002
Received on Monday, 4 December, 2000

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