Quality of Wood
One of the most important attributes of good furniture is the quality of the wood that is used. The figure or quality of wood is determined by a combination of factors based on the way a tree grows, on the cell structure of wood, and on the way wood is stored and seasoned. Wood is comprised of cellulose tubes which carry moisture and nutrients throughout the tree, and help give the tree its strength. Softwoods such as cedar, fir, pine and redwood are conifers, and have a rather simple cell structure composed mainly of long radiating tubes that carry the nutrients. Hardwoods such as mahogany, oak, chestnut, basswood and elm are deciduous, and have a more complicated cell structure composed of tubes and pores. New wood is produced annually by these cells and is the area between the bark and the center of the tree, or the heartwood. This annual new growth is called sapwood and is made of cells that carry nutrients both horizontally and vertically. Vertical or "ray" cells are more pronounced in hardwoods than in softwoods. At the end of the growing season sapwood is converted into heartwood, the strongest part of the tree. Therefore, heartwood increases in size each year, while sapwood is about the same size every year. The sapwood is furthur divided into earlywood and latewood. As the name implies, earlywood is the growth produced in the Spring or early part of the growing season, while latewood is produced in the Summer, or later in the growing season. If there is more growth early in the season than later in the season wood is said to be ring porous. If growth is more even during the growing season it is said to be diffuse porous and has a more evenly distributed grain, which makes the wood easier to work and finish.
Besides the structure of the wood, the manner in which it is stored and dried after harvest also determines the quality of the wood. Seasoning the wood, or drying the wood properly can affect quality. As much as thirty percent of the weight of green wood is moisture, and this moisture must be removed to prevent the wood from shrinking, warping and splitting. The moisture is removed by a combination of air drying and kiln drying, whereby the wood is stacked and exposed to a combination of air, heat and steam to gradually reduce the amount of moisture.
Quality wood should be strong, free from imperfections and have excellent grain and texture. Primary wood, or wood used for the pieces of furniture that can be seen, should be strong and have smooth, even grain and fine texture. Secondary wood, or wood used for parts of furniture that are not seen such as drawers and the insides of cabinets and upholstered furniture should be strong, straight, and free from warping, bending and splitting.
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