Series editors' preface - Wood Tools

2
Wood and wooden structures
It is essential for furniture conservators to
understand the properties and behaviour of
wood. Only when the underlying basis of the
working properties, identification and appearance
of wood is understood can conservators
make responsible decisions in their work.
Proper knowledge of wood as a material will
help in building an understanding of issues
such as deterioration, preventive conservation
and restoration. This chapter covers the structure
and properties of wood and how they
relate to each other. It also includes information
on the behaviour of wooden structures and
basic data on manufactured timber products.
2.1 Introduction to wood as material
Wood has always been indispensable to
human needs, and it is therefore not surprising
that we find wood at the heart of our cultural
heritage. Because of its unique physical properties,
wood holds honoured status as an engineering
material and functional commodity.
But the beauty of the material itself, when considered
with tactile properties and working
characteristics, assures that wood has prevailed
as a medium in the decorative arts. Although
the manner in which wood has been used
often takes advantage of its aesthetic values,
historical use is most closely related to its material
properties. Only by studying wood as an
engineering material, while remembering its
biological origin, can we fully appreciate the
craft and arts which developed around it.
The virtues and properties of wood are so
well known to everyone that it is sometimes
difficult to step back and consider them objectively
– and scientifically. Given that there are
tens of thousands of species that yield usable
timber, an obviously wide array of characteristics
can be expected. However, certain basic
features are common to all woody plants and
it is appropriate to begin by considering those
generalities which are most important yet generally
understated.
One idea is paramount: wood comes from
trees. While such a statement seems foolishly
elementary, it is fundamental to understanding
the complex nature of wood. Remembering
this basic reality will help to prevent or solve
many problems associated with wood. The
structure of wood is the outcome of a complex
series of chemical reactions. It begins with
photosynthesis, which takes place in the living
tree. Photosynthesis is the process whereby
carbon dioxide and water are converted, using
sunlight energy captured by chlorophyll in the
leaves, into simple sugars. These simple sugars
ultimately form both the food and structural
materials of the tree. The stem provides
mechanical support for the crown, serves as an
avenue of conduction between the crown and
the roots, and, on occasion, stores appreciable
amounts of reserve food material. Wood is
therefore strong yet, once seasoned, is relatively
light in weight, since its cells are then
largely full of air. Being of plant origin, it is
soft, in comparison with iron or stone (other
materials of equivalent strength), and is therefore
relatively easily worked, yet it is surprisingly
durable. These properties, together with
the rich variation in decorative characteristics
arising from grain patterns and colour markings
on the longitudinal surfaces, make wood
unique among building materials.
Although its fabrication and many of its
applications are comparatively simple, wood
itself is a substance of great complexity. To
make the best use of this material a degree of
49