Agar-wood, also known as oud, oodh or agar, is a dark resinous heartwood that forms in Aquilaria and Gyrinops trees (large evergreens native to southeast Asia) when they become infected with a type of mould. Prior to infection, the heartwood is relatively light and pale coloured; however, as the infection progresses, the tree produces a dark aromatic resin in response to the attack, which results in a very dense, dark, resin embedded heartwood. The resin embedded wood is commonly called gaharu, jinko, aloeswood, agar-wood, or oud (not to be confused with 'Bakhoor') and is valued in many cultures for its distinctive fragrance, and thus is used for incense and perfumes.
The odour of agar-wood is complex and pleasing, with few or no similar natural analogues. As a result, agar-wood and its essential oil gained great cultural and religious significance in ancient civilizations around the world.
As early as the third century AD in ancient China, the chronicle Nan zhou yi wu zhi (Strange things from the South) written by Wa Zhen of the Eastern Wu Dynasty mentioned agarwood produced in the Rinan commandery, now Central Vietnam, and how people collected it in the mountains.
Starting in 1580 after Nguyễn Hoàng took control over the central provinces of modern Vietnam, he encouraged trade with other countries, specifically China and Japan. Agarwood was exported in three varieties: Calambac (kỳ nam in Vietnamese), trầm hương (very similar but slightly harder and slightly more abundant), and agarwood proper. A pound of Calambac bought in Hội An for 15 taels could be sold in Nagasaki for 600 taels. The Nguyễn Lords soon established a Royal Monopoly over the sale of Calambac. This monopoly helped fund the Nguyễn state finances during the early years of the Nguyen rule.
Xuanzang's travelogues and the Harshacharita, written in seventh century AD in Northern India, mentions use of agarwood products such as 'Xasipat' (writing-material) and 'aloe-oil' in ancient Assam (Kamarupa). The tradition of making writing materials from its bark still exists in Assam.
Agar-wood is known under many names in different cultures:
It is known as chénxiāng (沉香) in Chinese, "Cham Heong" in Cantonese, trầm hương in Vietnamese, and jinkō (沈香) in Japanese; all meaning "sinking incense" and alluding to its high density. In Japan, there are several grades of jinkō, the highest of which is known as kyara (伽羅).
Both agarwood and its resin distillate/extracts are known as oud (عود) in Arabic (literally "rod/stick") and used to describe agarwood in nations and areas in Arabic countries. Western perfumers may also use agarwood essential oil under the name "oud" or "oude".
In Europe it was referred to as Lignum aquila (eagle-wood) or Agilawood, because of the similarity in sound of agila to gaharu.
Another name is Lignum aloes or Aloeswood. This is potentially confusing, since a genus Aloe exists (unrelated), which has medicinal uses.
In Tibetan it is known as ཨ་ག་རུ་ (a-ga-ru). There are several varieties used in Tibetan Medicine: unique eaglewood: ཨར་བ་ཞིག་ (ar-ba-zhig); yellow eaglewood: ཨ་ག་རུ་སེར་པོ་ (a-ga-ru ser-po), white eaglewood: ཨར་སྐྱ་ (ar-skya), and black eaglewood: ཨར་ནག་(ar-nag).
In Assamese it is called as "sasi" or "sashi".
In Papua New Guinea it is called "ghara" or eaglewood.
In Thai language it is known as "Mai Kritsana" (ไม้กฤษณา).
In Tamil it is called "akil" (அகில்) though what was referred in ancient Tamil literature could well be Excoecaria agallocha.
In Laos it is known as "Mai Ketsana".
There are fifteen species in of the Aquilaria genus and eight are known to produce agar-wood. In theory aga-rwood can be produced from all members; however, until recently it was primarily produced from A. malaccensis. A. agallocha and A. secundaria are synonyms for A. malaccensis. A. crassna and A. sinensis are the other two members of the genus that are usually harvested.
Formation of agar-wood occurs in the trunk and roots of trees that have been infected by a parasitc ascomycetous mold, Phaeoacremonium parasitica, a dematiaceous (dark-walled) fungus. As a response, the tree produces a resin high in volatile organic compounds that aids in suppressing or retarding the fungal growth. While the unaffected wood of the tree is relatively light in colour, the resin dramatically increases the mass and density of the affected wood, changing its colour from pale beige to dark brown or black. In natural forest only about 7% of the trees are infected by the fungus. A common method in artificial forestry is to inoculate all the trees with the fungus.
High quality resin comes from a tree's natural immune response to a fungal attack. It is commonly known as agar-wood number 1 (first quality). An inferior resin is created using forced methods where aquilaria trees are deliberately wounded, leaving them more susceptible to a fungal attack. This is commonly called agar-wood number 2 ( second quality).
A natural perfume oil obtained by CO2 extraction from agar-wood retains the odor of "true" agar-wood: a cepes (mushroom) and carrot seed accord, which can be roughly approximated by combining ambergris, jasmine, earth and wood notes. Lightly infected wood, sometimes cultivated, produces an (allegedly) inferior oil with a vetiver, sandalwood, and patchouli character.
Hydro-Distillation process used to extract agar-wood essential oils.
Article extracted from Wikipedia