Wood identification

Identification of furniture woods plays a vital part in historical studies and in the authentication of furniture. In addition, identification enables the furniture conservator to select the most appropriate materials for a good match to the original. Traditionally, wood identification in furniture focused on the principal primary wood or woods as a fashionable reference to the objects. We routinely refer to a card table as 'a mahogany card table'. But increasingly it is considered important to evaluate all wooden components, primary and secondary, as critical information in the analysis and attribution of an object. In identifying wood, the usual objective is to determine the species of the tree from which a particular piece of wood was obtained. Whether or not this goal can be achieved is dependent largely on the wood in question, namely, whether or not the particular wood has physical and anatomical characters that distinguish it from all others. Many woods cannot be separated on their wood anatomy to a single species (e.g. Tilia sp.). In applying wood identification to interpretative analysis, it is important to know the level of identification possible as well as the geographic ranges of the woods under consideration.

Unfortunately, there is no single technique or method of wood identification which fits every situation or which is best for every species. An identification procedure often begins by taking advantage of any obvious or unique features, such as unusual colour, recognizable odour, distinguishing figure, or extremes of density, which immediately suggest the identity of the wood. Occasionally, the answer is immediate, as from the unusual weight and dotted pigmentation of snake wood or the distinctive bee-wing figure and golden colour of satin wood. Usually, however, visual or tactile hints must be checked by more precise and reliable means. Ultimately, wood identification requires the presence of a defined set of known features that will verify each species encountered. These may be macroscopic features, microscopic features, or a combination of the two. Anatomical features of an unknown are assessed and compiled for comparison with known features of familiar woods, with information in anatomy texts or computer databases, or with direct observations of actual reference specimens.

Many publications on wood anatomy include dichotomous keys. These keys are based on a system that offers (usually) two options at each stage in the selection process. Only one feature can be selected, which leads to the next two options. At the final stage, one or more taxa are suggested as possible candidates for the unknown wood. The final result always has to be checked against reliable reference material. Keys exist for specific regions, for example, Grosser (1977) and Schweingruber (1990) have keys for Europe, and Panshin and deZeeuw (1980) have a key for the United States. In the UK, the Timber Research and Development Association (TRADA) has published simple keys of this type for both hardwood and softwood identification. Dichotomous identification keys, accompanied with 10X to 15X photographs of transverse cross-sections of wood provide useful supportive data with the hand-lens identification method (Normand, 1972). The main disadvantage of this approach is that no match will be found when that particular genus or species is not included in the key, means that it is often useful to adopt a more flexible approach (Brazier and Franklin, 1961; Hoadley, 1990).

Multiple entry key systems exist that are based on either perforated cards or computer systems. Examples of multiple entry perforated card systems are published by the Forest Products Research Laboratory (FPRL) and described by Brazier and Franklin (1961), Phillips (1960) and Henderson (1960). Multi-entry computer sorting systems have been developed based on the traditional FPRL perforated card system. Especially within the International Association of Wood Anatomists (IAWA), there is an ongoing discussion about some of these programs, combined with reviews of suitable wood anatomical features. The General Unknown Entry Search System (GUESS) by Wheeler (Wheeler et al, 1986) is a useful and inexpensive PC program containing more than five thousand taxa in eight different databases, and is accompanied by an excellent textbook. Miller (1980), and Miller et al. (1981, 1987) has described more elaborate systems that operate with a larger number of features. Other programs were developed for specific regions or countries. Jiaju and Fang (1990) describe the Wood Identification Program (WIP) for woods mostly from China. A review of current computer search programs is given by Wheeler and Baas (1998).

Reference material should consist of microscope slides made of vouchered wood samples, wood descriptions and photo-micrographs of wood sections (D├ętienne and Jacquet, 1983; Fahn et al., 1986; Grosser, 1977; Miles, 1978; Panshin and deZeeuw, 1980; Schweingruber, 1990). Vouchered wood samples are specimens of woody plants of which the leaves, fruits or flowers also were collected of the same exact plant, and identified to the species level for taxonomic purposes. Gregory (1980) provides an annotated bibliography on wood identification including a listing by botanical family, growth regions and microscopic features with cross references to more than 450 bibliographic entries.

Wood identification is typically an invasive and destructive process, at least to the extent that some wood tissue must be disturbed. The process usually consists of removing small samples or sections, or at least in cleanly cutting into a surface to expose cell structure for examination. In identifying woods of historic objects, a primary responsibility is to utilize approaches that accomplish identification with the least possible disturbance to the object.

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