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In these documents, and in practice, there can be a tension between the terms,
or rather interpretation of, preservation and conservation. The Venice Charter,
for example, states that removal of material should be viewed as the last option
in any restoration work. This can be extended to a general interpretation of
preservation as a philosophy that puts a premium on retaining any monument
as it stands. It is a philosophy that is static and rigid in its view of a monument –
it should be frozen as it is now, as a snapshot in time. Conservation could be
viewed as a more fluid and dynamic philosophy that sees a monument as a
dynamic and holistic entity, something that changes, that is part of its context
and informed by that context. Conservation accepts a balance needs to be
struck between preservation and change. A building is designed, built and
maintained using the methods available at the time. Building practices change
over time and repair work is probably carried out using best, or appropriate,
contemporary practices. This means that the building as it is now is unlikely
to be a pristine example of traditional practices of a given period. A building
is more likely to be a reflection of building practices of different periods.
An important question arises: what is it that is being conserved?A building
can be thought of in a number of ways. It is constructed of a variety of materials
in varying states of degradation. A building is more than individual blocks of
stone, it is also a representation of an architectural plan. Which of the above is
the focus of conservation and can the two be separated? The distinction is vital,
because if the material used is not integral to the representation of the design,
then why preserve the material? There may be no easy answer to this ques-
tion as the design and the material are interwoven, but understanding why
particular materials were selected, and how they might be improved or
replaced without affecting the representation of the building, is important
within conservation.
Conservation does not imply a single approach or method. There are a range
of techniques that can be employed. Each technique should, however, be
assessed on the basis of a set of criteria before any conservation practices are
used. These are reversibility, compatibility, re-treatability and effectiveness.
Reversibility refers to the ability to reverse the effects of any treatment. Often
the changes that treatments are designed to produce are intended to be irre-
versible, such as the removal of black crusts by washing. Compatibility refers
to the neutral or positive impact of treated materials in a building with the
untreated materials. It implies that treated materials should have physical
and chemical properties compatible to those of the untreated material. This
should ensure that physical and chemical interactions between the two are
not harmful to the ‘traditional’ materials. This criterion also means that it may
be inappropriate to use the most modern methods if the results could have a
harmful effect on the rest of the building. This could be viewed as implying
that there are different tolerance limits for altering material properties by