Consolidation of wood

Lori Arnold <larnold [at] johnmilnerassociates__com> writes

>Subject: Consolidation of wood
>
>Michelle C. Messinger <mcmes [at] parks__ca__gov> writes
>
>>I like to know what kind of experience any one has had with linseed
>>oil in turpentine and paint thinner as a wood consolidant. How does
>>it effect the wood? ...
>
>There are a few problems associated with linseed oil. Yes, it is
>somewhat reversible, but difficult to remove--especially with
>turpentine as a carrier. If not removed completely, it can
>compromise future treatments that may be applied to the wood.
>
>The major drawback to linseed oil is it's tendency to oxidize by
>turning yellow and crazing over time. While certain beetles are
>quite fond of it, it is also notorious for attracting dirt. It will
>not form a hard film as it does in the context of paint, but will
>give you a temporary look of "freshened" wood.

This discussion reminded me of an experience I had at the Istituto
Centrale per il Restauro in Rome in 1996-97, which shows that the
treatment regimen described above is still in use, in places where
it ought not be.

The circumstances were as follows. The ICR ran a course to train a
group of 5 young people to restore pipe organs with a small amount
of theoretical preparation and some practical experience on the
organ of S. Maria in Trastevere (Rome), dating from 1701-2.

The rackboard (a large horizontally-mounted wooden panel with holes
for the pipes which stands above the windchest and is designed to
hold the pipes in a vertical position), in this case made of pieces
of poplar about 1 cm thick, attached to a frame of chestnut was
treated by the application of several generous coats of linseed
oil/turpentine followed by an equally generous application of
beeswax. The wooden panels were severely dessicated and had clearly
been attacked by borer. There were galleries created by other larger
insects. Shrinkage had caused the poplar panels to split in various
places.  The gaping cracks were filled in using pieces of new
(seasoned) poplar which were glued in place using hide glue before
the oil treatment.

Given the comments above you may well ask why such a treatment was
adopted. A few years ago, a commission was formed to attempt to
create guidelines for the restoration of historic organs in Italy.
The commission (now disbanded) came up with a series of
recommendations, one of which states that the procedures adopted
should be reversible and that technologies which are analogous to
the craft techniques of the author should be employed. These
recommendations have been printed and disseminated in _Conservazione
e restauro degli organi storici_ edited by G. Basile and published
by the ICR in 1998 (p171-173).  (Basile was also a member of the
commission and director of the course concerned.)

It should be obvious that the two goals (reversibility, use of craft
techniques) are generally difficult to reconcile with each other.
However, since most of the practitioners in this field have no
knowledge of conservation techniques or objectives, the commission's
recommendations make perfect sense to them, being totally unaware of
the implications of that treatment.

One of the primary goals in this scenario is on functional
restoration of the instrument(s) concerned, and it seems there is a
belief that craft methods ensure that the aesthetic/cultural value
of the object is less prone to "pollution" than it would be if other
methods were used. Ironically, in terms of functionality, the
rackboard would have been much more mechanically stable (and
therefore functionally better able to carry out its job) had a more
appropriate consolidation treatment been adopted. The functional
requirements would also have been better served by using a treatment
which had a relatively greater "reversibility coefficient" (my term)
than the one used. Furthermore, the use of a wet abrasive cleaning
technique prior to the linseed oil treatment resulted in the loss of
the original builder's inscriptions on the underside of the panels.

Apart from the single episode described above, the restoration of
this instrument is an interesting case for other reasons. As I
mentioned above, the whole process took place in the context of a
training course organised by the ICR. An extensive documentation
processes of all facets of its treatment was also undertaken, and
includes a detailed description of treatment procedures for almost
every component. It is instructive to read the documentation in the
light of the commission's directives to see the manifest tension
between craft methods, conservation, and functional requirements.
Reading the material which was published in local journals around
this time, it is evident that the promotion of craft methods was
intended to try to stop the rebuilding of these instruments
incorporating modern technologies (electric action etc). Ironically,
what was initially a directive aimed at promoting preservation has
turned into another kind of threat.

Nicolaas Waanders


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                  Conservation DistList Instance 15:23
                Distributed: Tuesday, September 11, 2001
                       Message Id: cdl-15-23-001
                                  ***