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Topics
Density
Appearance
Colour Permanence
Figure
Lustre
Other Characteristic
The common range in the air drying density of plywood and veneer species is approximately 0.40g/cm3 to 0.70g/cm3 with preference for species about 0.50g/cm3 to 0.55g/cm3(Baldwin 1981). A few species are used below the lower limit, but low density woods have the disadvantage of being too soft for most uses.
High density is not necessary for structural grades of plywood, even though higher strength properties are normally associated with higher density. High density wood does stand up better to wear, and are suitable for products involving frequent re-use (concert formwork), abrasion resistance (flooring).
Colour is one of the most important appearance characteristics of decorative veneers or panels. Sometimes a fairly even colour is desired, at times value lies in marked contrast. The contrast between light sapwood and dark heartwood although occasionally accepted and used effectively, is usually not desired. Colour is largely a matter of fashion never the less, some woods such as the traditional furniture woods, such as mahogany and walnut are always acceptable
Associated with colour is colour permanence. Some woods change colour when exposed to light for long periods and the change may be undesirable Closely allied to colour is bleach ability for producing light colour and stainability for darker colour.
Veneer cutting and arrangement give the maximum outlet for figure exploitation. Figure can be due to contrast across the width of a growth ring arising from density change or from pore arrangement, to colour variations not necessarily associated with growth rings, to medullary rays which can produce a lace like effect or a fine ripple tangentially. Thin walled parenchyma cells contribute most to appearance when they are in concentric bands, or surrounding the vessels which then become accentuated without being undesirable large in size.
Lustre, which can be describe as the variation in reflection from the surface of fibres according to the angle of viewing, is a most important characteristic of wood(Baldwin 1981). It gives depth to the figure of the wood and a variation in the colour pattern according to the direction from which a panel is observed. This characterise is known as "life" in the wood, it varies from species to species, and is generally more prevalent in hardwoods than softwoods. This feature has not yet been secured in printed reproductions of wood surfaces.