Casting techniques for wooden carving

Frank Hassard <f.hassard [at] tiscali__co__uk> writes

>I am working on a reproduction Chippendale cabriole leg chair
>(c.1860) carved in mahogany. One of the ear-pieces to the top of the
>proper right side is missing. ...
>...
>... I think it may be possible to cast a new one from one of the
>existing ear-pieces (and then tailor it to suit). However, I do not
>have much experience with such techniques. I understand that there
>are concerns with some of the epoxy systems regarding
>discolouration, texture etc. Could someone give me some advice on
>how to get the best results and which materials/techniques are
>presently favoured (and ethically acceptable)? ...

One option in such a situation would be to scan the existing ear
piece using a 3d laser scanner--in this case it would have to be a
highly accurate sub-millimetre scanner that was employed. Once the
3d data had been recorded from the original, it can easily be
mirrored (if required) to create the missing piece. From the
completed data set a new piece could be machined (using a Computer
Numerically Controlled CNC machine, where the tool path of the drill
is controlled by the 3d data provided) into wood, or another
material (such as a cast resin), if it was deemed that you wanted it
to be obvious that the piece was a later addition.

Alternatively, a master could be machined, or made by rapid
prototyping technologies--where modern materials are built-up layer
by layer using the 3d data as the template. From this master, a new
piece could be cast using traditional techniques. These methods,
although by no means the only, nor necessarily the most appropriate
in every case, do mean that there is no contact with the original
object's surface at any time during the process, thereby totally
eliminating the risk of staining, discolouration, or of damaging
friable surfaces. We have been using such methods in conservation,
here and elsewhere for 8 years with excellent results, in cases
where the original is too friable or sensitive to be replicated
using traditional techniques.

Annemarie La Pensee
Laser Technology
Research Scientist
National Museums Liverpool
+44 151 478 4915
Fax: +44 151 478 4810


                                  ***
                  Conservation DistList Instance 19:51
                  Distributed: Friday, April 21, 2006
                       Message Id: cdl-19-51-011
                                  ***