Logwood is a dye-producing tree legume originating in Central America, its natural range extending from southern Mexico to neighbouring Guatemala and Belize. Introduced long ago into other parts of tropical America, it is now naturalised across Central America, the Caribbean and northern South America.
It is a small, thorny deciduous tree 5 to 10 m (16 to 32 ft) tall, typically with a short trunk or with multiple stems supporting a rounded crown of arching, gently drooping branches. The upright stems are twisted or deeply fluted and covered in grey or brown bark, becoming cracked, rough and flaking with age.
The leaves are 5 to 12 cm (2 to 4.7 in) long and feathery, being composed of light- or dark-green, wedge-shaped leaflets arranged in pairs along the length. They fall off the tree in the dry season to conserve water, leaving the branches partially bare until new leaves emerge, which is at the start of the rainy season.
The flowers are small, light yellow, five-petaled, ill-scented and borne in cylindrical clusters up to 7.5 cm (3 in) long arising at the leaf bases. They come into bloom in the dry season and are followed by flat seedpods 2 to 5 cm (1.2 to 2 in) long, becoming dry, light brown and with up to three flat brown seed inside.
The wood yields a valuable dye in the blue to purple colour range. Known as 'Logwood dye', it has long been used by indigenous Americans to colour fabric woven from cotton and wool. After the arrival of Europeans, it developed into an important commercial dye for the clothing and medical industries.
Only the brownish-red heartwood contains the dye, which soon after harvesting is stripped of the surrounding sapwood.
To make the dye, the heartwood is finely chipped, covered in boiling water and then left to soak for up to twelve hours. This causes the chips to ferment and the dye to leach into the water. More water is then added and the chips simmered over heat for twenty minutes, which completes the process of making the dye-liquor. In commercial operations, the dye-liquor is dehydration under vacuum to produce dye crystals
Different colours are obtained by adding different mordants. Alum (aluminium) gives purple shades but needs to be combined with copper or iron to increase colour-fastness. Copper by itself gives a blueish hue and iron dark purple to black, depending on the amount added.
Fibre and fabric dyed with logwood dye needs a hot dye bath, with simmering over heat for about forty-five minutes and then with soaking until cool to give a good colour. Repeated rinsing several times after dying is reportedly critical to reducing 'dye bleed', which is when the dye leaches out of the fabric.
Logwood dye was once used as a colouring agent in black hair colouring and to neutralise red tones in dyed hair. It is also the source of haematoxylin, a staining agent long used in cytology and histology to differentiate between different parts of biological matter, usually at the cell level and in examination under a microscope.
The flowers produce abundant nectar and it is reported as a major nectar source and honey plant throughout its native and non-native range. Nectar flows can be heavy and long-lasting in plants with access to water, through either groundwater or rainfall. Pure logwood honey is light amber to almost white and reported yields have been as high as 200 kgs (440 lbs) per colony per season.
The wood is hard and heavy, in the 960 to 1040 kgs per cubic meter (60 to 65 lbs per cubic ft) range and is naturally resistant to rot and decay, but comes in logs too small and poorly-formed to make sawing them into lumber piratical. Where they are not harvested for their dye, the stems are cut for fence posts and make an excellent firewood and charcoal.
In his song 'No woman no cry', Bob Marley makes reference to the use of Logwood as firewood, in the the verse 'Georgie would make a fire light, as it was logwood burning through the night'.
Grows naturally in sub-humid to moderately humid tropical lowland climates, generally in frost-free areas with annual lows of 18 to 25 °C, annual highs of 27 to 35 °C, annual rainfall of 900 to 2000 mm and a dry season of 3 to 6 months.
Logwood has long been introduced in Jamaica and has become naturalised there, mainly on the south coast of the island, at elevations from near sea level up to 460 m (1500 ft).
New plants are usually started from seed, which remain viable for up to eight months under cold, dry storage and germinate readily, with about half sprouting after three weeks.
Performs best on free- to slow-draining clay, loam, sand and gravel soils of a moderately acid to alkaline nature, generally with a pH of 5.5 to 8.5 and on sites with full to partial sun exposure. Has good tolerance to seasonal flooding and poorly drained, swampy soils, though heavy soils are reportedly unfavourable to the production of the dye.
Stems harvested for extracting the dye are usually ready to be cut when the plant is about ten to twelve years old.
The plant produces a large amount of seed that germinate readily. Logwood, if left unmanaged, can form dense, impenetrable thickets over time.
Logwood is recorded as a weed of the natural environment in countries such as Australia and as an invasive species in the Caribbean, a term only applied to serious, high impact weeds. It is assessed as a high weed risk species for Hawaii, by the Hawaii Pacific Weed Risk Assessment project (HPWRA).
The branches are armed with sharp thorns or spines that can inflict injury on the unwary.
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