Information Technology Reference
In-Depth Information
its name derives. 'Old Cape furniture' refers to furniture produced in the Cape region in
South Africa during 1652 - 1900 according to the prevailing Western styles. Stinkwood
was one of the principal woods used in the Cape during the 18th and 19th centuries
for the manufacture of chairs, cupboard panel surrounds, fronts of drawers, framing and
styles of doors. The kind of wood used plays an important role in the buying and selling
of old Cape furniture. Furniture made from stinkwood alone, or from a combination of
stinkwood and yellow wood, has a high prestige value. It is therefore important that
the private owner, as well as the trader, must be able to accurately identify the kind
of wood. Many people working with antiques claim that they can identify the wood by
visual inspection. However, it is clear that in most publications on old Cape furniture,
even where in-depth research was conducted, information on the kind of wood used is
very scant. The identification of the kind of wood is usually based on face value and
according to tradition. The importance of the scientific identification of the kind of wood
becomes critical when authors contradict each other; for example, Botha (1977) states
that the 'tolletjiestoel' was usually made of stinkwood but Baraitser and Obholzer (1981)
declare that it was rarely made of stinkwood, yellow wood or teak. South Africa is a
country with few indigenous timbers. It was thus imperative that wood was imported.
Imbuia (
O. porosa
) was one of the woods imported from South America and eventually
became an accepted substitute for stinkwood. Swart and Van der Merwe (1980) describe
the identification problems concerning
O. bullata
(indigenous stinkwood) and
O. porosa
(exotic imbuia). Both are species from the genus
Ocotea
from the family
Lauraceae
.
The substantial price difference between furniture made from these two species from one
genus necessitates accurate discrimination.
Swart (1980) gathered research material with nondestructive measures from two
indigenous species of the
Lauraceae
family:
O. bullata
and
O. kenyensis
. Both qualitative
and quantitative wood anatomical features were measured. In the first phase the genus
Ocotea
was distinguished from the other species in the family, using mainly microscopic
qualitative anatomical features. Based on these features, the indigenous
Ocotea
species,
as well as the exotic imbuia, could be positively identified as belonging to the genus
Ocotea
. In a second phase, distinctions were required between the species within the
genus. The two indigenous species
O. bullata
and
O. kenyensis
, and also the two furniture
woods
O. bullata
and the exotic
O. porosa
(imbuia) must be differentiated. Up to that
time these distinctions were based on physical macroscopic features such as colour and
smell, but the large variability in these features leads to very subjective identifications.
A controversy about a 19th-century Cape chair was the primary incentive for this
example, originally discussed by Burden
et al.
(2001) and Le Roux and Gardner (2005).
The data given in Table 3.9 show the wood anatomical features of 20
O.bullata
,10
O.porosa
and 7
O.kenyensis
samples investigated by Swart (1985). For each of the 37
samples, 50 microscopic measurements were made on each of the six variables discussed
in Section 3.4. The mean values of the 50 measurements for each of the samples were
calculated for each of the six wood anatomical features. These mean values were used
as the observed values for each of the samples, thus forming the data set given in
Table 3.9. Recall that a predictive PCA biplot of the scaled
Ocotea
data set is given
in Figure 3.23, showing the mean vectors of
O.bullata, O.porosa
and
O.kenyensis
.The
sample predictivities of the mean vectors are given in Table 3.14. Before considering
a CVA biplot of the
Ocotea
data, we reflect on some aspects of the PCA biplot in
Figure 3.23 and the function
PCAbipl
for creating it. First of all, we remember that
