Casting

Margaret Contompasis <mcontomp [at] indiana__edu> writes

>The Indiana University Art museum needs to explore options for
>making a replica of a 15th century bronze sculpture of Parvati in
>good condition. ...

I am the objects conservator working with Factum Arte, a company
based in Madrid and London, specializing in the documentation of
cultural heritage, the production of replicas and other projects
with contemporary artists. Most of the work we undertake involves
digital mediation during various stages of the process. I suggest
that you look at
<URL:http://www.factum-arte.com/eng/conservacion/barron/default.asp>
especially the project we are currently working on to make a copy in
bronze of a life-sized sculpture of Seneca and Nero in the Museo del
Prado.

This project has involved the use of both our own laser scanner
(known as the Seti Scanner and developed with 3D Scanners UK for use
in the tomb of Seti I) and a white light scanning system developed
by the Spanish company NUB3D. The Seti scanner captures an ordered
point cloud on a grid of 100 microns and requires almost no post
processing. The NUB 3D records lower resolution data (a grid of
about 300 microns) but it can record sculptures in the round and
large complex objects.

For the production of any accurate replica it is essential that the
data should be of the highest quality. Today, most scanning systems
can provide data that is adequate for screen-based applications such
as virtual reality. The production of physical replicas requires
significantly higher resolution data, which is then difficult to
handle during the processing that is required for 3D fabrication.

The usual solution is to optimize the data lowering the resolution.
This is effectively a process of averaging the data resulting in a
smoothing of the surface and the loss of measured points with a true
correspondence to the surface. The knock-on effect is that the 3D
model is not crisp enough and lacks the necessary detail to convince
the eye. Our approach is to scan at the highest possible resolution
while minimizing all aspects of the post-processing. Importantly the
high-resolution data forms a valuable archive for the monitoring of
the sculptures condition.  It is also an important resource for
research.

Producing the bronze replica of Seneca and Nero presented very
specific problems in terms of data management, especially in terms
of the software used to run the different stages of the process. The
solutions we found to these challenges were all achieved without
significant alterations to the point cloud.

Depending on the complexity of the surface, making a replica of a
bronze sculpture of Parvati will probably involve a similar
approach. Factum Arte has extensive experience of bronze casting
using loss wax, ceramic shell and sand casting techniques.

A previous project, to record and create a replica of the limestone
bust of the Dama de Elche (Museo Arqueologico Nacional) presented
the opportunity to make direct comparisons between 3 different
scanning systems and the results of these tests can also be seen on
the website.

The importance of independent tests like this cannot be overstated.
The documentation that accompanies the different scanning systems
make claims for the resolution of the data that can be recorded but
experience often tells a different story. With most new technologies
mistakes can prove to be very time consuming and expensive. We are
both interested in testing existing equipment under working
conditions and developing new systems specifically for use with
cultural applications.

Naoko Fukumaru
Objects Conservator
Factum Arte
C/ Hilarion eslava 53
Madrid 28033, Spain
+34 91 5500978
Fax: +34 91 5495935


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                  Conservation DistList Instance 20:25
                Distributed: Saturday, November 11, 2006
                       Message Id: cdl-20-25-002
                                  ***