|Common Names (Dyestuff):||bloodwood, brasiletto, campeachy, haematein, hematein, hematoxylin, Haematoxylum brasiletto, Haematoxylum campechianum, logwood, palo de brasil, palo de tinto|
Origin and History
Early in the 16th century, the Spanish discovered a tree in Yucatan with a deep red heartwood similar to brazilwood. The tree became known as logwood (Haematoxylum campechianum), and by the late 1500s Spanish ships were exporting large cargoes of the valuable heartwood from the Yucatan coast. The generic name of logwood Haematoxylum (often spelled Haematoxylon) means bloodwood, referring to the dark red heartwood. The specific epithet campechianum refers to the coastal city of Campeche on the Yucatan Peninsula, the type locality and important source of the valuable heartwood. Early in the 18th century logwood was introduced into the West Indies and other Caribbean islands where it became naturalized. On some islands such as Haiti and Jamaica, large areas of tropical vegetation have been denuded due to logwood cutting on plantations. Logwood dyes were used extensively for dyeing cotton and wool cloth, leather, furs, silk, and in making ink. They were also made into lake pigments and used in easel paintings throughout Europe since the early 17th century.
Logwood is a small, spiny tree with a peculiar deeply-fluted or corrugated trunk that appears like a cluster of stems fused together. The pinnate leaves consist of several pairs of reverse heart-shaped (obcordate) leaflets. Showy yellow blossoms appear throughout the year and are typical of the subfamily Caesalpinioideae, with five spreading petals. The papery seed pods are unusual among legumes because they split down the middle instead of along the edges. The wood is very hard and dense, freshly cut stems readily sink in water. The dark heartwood is the source of the brilliant red dye hematoxylin, with a chemical structure practically identical to brazilin.
Another lesser-known Mexican species of logwood is called "palo de brasil" or "palo de tinto" (Haematoxylum brasiletto). It has a remarkable distribution from desert hillsides and arroyos of Sonora and Chihuahua, extending south through tropical dry forests of Oaxaca, Guatemala, Costa Rica and Colombia. The deeply fluted, corrugated trunk of Mexican logwood or palo de brasil is similar to Belize logwood. This species has a remarkable distribution from desert hillsides and arroyos of Baja California and Sonora, Mexico, extending south through tropical dry forests of Oaxaca, Guatemala, Costa Rica and Colombia. The flowers are typical of the pea subfamily Caesalpinioideae with five spreading petals, unlike the typical pea blossoms of subfamily Papilionoideae.
The dye from logwood, hematoxylin, is a complex phenolic compound similar to the flavonoid pigments of flowers. The chemical structure of hematoxylin is practically identical with the dye brazilin from brazilwood, except that hematoxylin has one additional atom of oxygen. Hematoxylin is extracted by boiling chips or shavings of logwood in water. The presence of a considerable amount of tannin in the purplish-red dye bath allows the logwood extract to react with iron salts to give a permanent black color.
Preparation of Lake Pigment
Pigments and dyes are not identical, although there are cases in which the same coloring matter which yields a dye or stain may give rise to a pigment. A pigment is, in fact, a substance which is insoluble in the vehicle with which it is mixed to make a paint, while a dye is soluble. A lake pigment is a natural organic pigment prepared when a dye has been precipitated on a powdered, colorless, inorganic substrate. The term derives from the Latin word lacca, used in the Middle Ages to denote both lake pigments and the Lac dye. Because of its transparency, aluminum hydroxide is the most commonly used substrate or carrier. Barites, such as barium sulfate, provide an opaque lake pigment. Other compounds used as carriers are: chalk, clay, gypsum, tin oxide, zinc oxide, white earth, and green earth. Often a mordant, such as tannic acid, lactic acid, or sodium phosphate, is used to fix the dye to the substrate.
The dye is extracted from logwood by the boiling brownish shavings in water over steam under pressure. The red-brown hematein crystals are sparingly soluble in water. With sodium hydroxide, there is formed a purplish-blue solution which changes to brown on exposure to air. Brown, reddish-brown, black, and blue-black lakes can be prepared from logwood extracts with various mordants. When treated with bichromate, it was formerly used in the manufacture of inks. Most logwood lakes were made either from the extract made with la weak solution of potassium carbonate or made with aluminum sulfate (alum), as these solutions get the color out of the wood more thoroughly than plain water. Just what the shade is that is extracted depends on how acid or alkaline the mixture of solutions is made. The more alum, the warmer the color, the more potassium carbonate: the colder the hue. The precipitate is collected by settling and pouring off the liquid. The pasty mass is smeared on an absorbent surface such as a new brick or tile to dry. Then it is ground, and has the same degree of transparency as the mordant of which it is chiefly composed. When chalk is added to the mordant, a more opaque pink rose is produced by the resulting admixture of calcium sulfate to the lake. When white lead was used, it had no other effect than to give substance to the lake and slightly less transparency, rather than to make it opaque. When marble dust and powdered egg shells were added to newly formed lakes, they further controlled the color produced by reacting chemically with any excess of alum which might give a brown cast instead of rose. In all these cases the logwood color was mordanted upon the white material, so to speak, dyed with the logwood, and the pigment so formed was different from a mixture of a finished lake with a white pigment.
Permanence and Compatibility
Lake pigments made from logwood are not considered to be permanent, lightfast colors. The lakes are insoluble in water and in alcohol but are turned bluish-black by alkalis, and are decomposed by mineral acids with the formation of a blood-red solution. They are not stable in strong light.
Oil Absorption and Grinding
No data has been published on the oil absorption and grinding qualities of lake pigments made from logwood.
The essential coloring matter of the logwood is considered to be non-toxic.
|Colour Index:||Natural Black 1 (75290)|
|Chemical Name:||Hematoxylin (leuco form), Hematein (oxidized form)|
|Chemical Name:||C16H14O6, C16H12O6|
|ASTM Lightfastness Rating|
|Processing Time||Usually ships the next business day.|
|Size||100 g jar|