The Technique of FURNITURE MAKING

Coloration

The natural colouring agents in wood are water soluble, and will tend to leach out if repeatedly soaked or exposed to weathering for long periods. Typical colour examples are logwood, which yields a commercial water soluble fierce red dye, and fustic a khaki yellow. Generally speaking, wood is lighter in colour when freshly sawn and gradually darkens as the wood surfaces oxidize, but as the colours are not permanent they may ultimately fade. The sapwood is usually lighter than the heartwood, and this serves as the usual method of identification; but some species exhibit little if any difference, notably ash, sycamore, beech, holly, silver fir, etc.

The precise description of colour in any specimen is virtually impossible, as so many factors apply. No two trees are ever alike, and at best a wood can only be described as having general characteristics modified or accentuated by growth conditions, exposure to air, heat, sunlight, etc. In general, most woods, with the exception of jet-black ebonies and blackwood, and pure white holly, have a yellowish cast which can never be bleached out completely. It is this predominant yellow in conjunction with reds and blacks which give the innumerable shades of brown. Greens do exist, but are usually the result of abnormalities, while clear greys are the result of weathering or treatment by chemical means.

Woods which change colour under normal indoor conditions, with only occasional exposure to direct sunlight, include the following:

Those which fade - rosewood, walnut, mansonia. teak, agba, gaboon, etc.

Those which yellow - African mahogany, sapele. walnut (most species), agba, gaboon, maple, plane, sycamore, oak, etc.

Those which redden - cherry, yew, beech, kingwood. purpleheart, padouk, etc.

The lists are by no means complete, and individual specimens may not necessarily behave in the manner indicated, while all polishes tend to darken wood in time, and oil and wax pronouncedly so.

Odour

Most timbers have trace odours, some very pronounced, due to the presence of essential oils which often decide the use of the wood. Notable examples are cedar, camphorwood, etc. Some timbers are also known by their particular scent or odour, such as sandalwood, rosewood, jamwood, sneezewood, stinkwood, etc. Teak, Australian walnut and certain African woods have a highly objectionable smell when freshly worked; but most scents and odours, with the notable exception of camphor and cedar which are used as moth deterrents, rapidly fade on exposure to the air, due to the surface evaporation or drying out of the essential oils.