One of the biggest choices in guzheng manufacture is the woods that are used to create the instruments. Thanks to incredible work by Carol Chang of ChineseZither.net I have below a brief overview of the types of wood you might find and a guide on why words like "Sandalwood" and "Wutong" aren't as meaningful as they might seem.
Any wood can be used to make a musical instrument - but the woods listed in each section make instruments known for their sound.
The main wood used in modern soundboards is Paulownia elongata or Lánkǎo Pāotóng (兰考泡桐). It's a fast growing tree that was planted in large numbers in Henan province's Lankao county (兰考) in about 1965 to act as a windbreak to control dust and preserve farm fields. Someone realized it could make fine lumber for musical instruments, and suddenly the dust control measure became a money maker. (*)
But what about pre-1965 zhengs?
Paulownia fortunei or Báihuā pāotóng (白花泡桐) was a popular pre-1965 wood for instruments. It's from the same genus as the P. elongata and is still touted as the wood used in the qin.
Cunninghamia Lanceolota or Shānmù (杉木) is used for zhengs made in the Chaozhou style, named for what is now a city in Guangdong province in southeast China.
"Hey!" I hear you cry "What about 'Wutong wood' and 'Firmiana simplex'?? I see that everywhere!" Well, there's a (long) answer for that. I hope you brought snacks.
Common names, imprecise naming, and mistranslations make figuring out actual wood species a real challenge. Thankfully Carol Chang of chinesezither.net put in the work and I am eternally grateful to her for that. Let's get some terms out of the way:
Paulownia: That's a genus of tree with 8 accepted species and 18 Latin synonyms. Synonyms are proposed names that turned out to refer to an already-identified species.(1) Only some species are used for musical instruments.
Tóng (桐): A category of wood. The 1051 CE book "Tong Guide" (桐谱, Tóng Pǔ), the earliest reference I know of, lists six varieties of Tong. Only some of them are in the Paulownia genus, so "Tong" is not a direct equivalent to Paulownia. (2)
Pāotóng (泡桐): Modern Mandarin name for Paulownia.
Wútóng (梧桐): A name often given as the wood used in guzheng, but covers multiple species. A common translation for Wútóng is Firmiana simplex, but F. simplex is not the most popular wood used for guzheng soundboards (that honor goes to Paulownia), and the most knowledgeable source I have on this, Carol Chang, says F. simplex is a poor choice for a soundboard. Further evidence of these confusions come from ancient records. Those that praise "Wútóng" trees for their instrument-quality wood mention purple flowers. F. simplex flowers with green, yellow, or white-tinted blossoms. The only modern English language source I have that goes into detail about the construction of guzheng says that the Wútóng used in Taiwan for instruments is both Firmiana simplex and an unknown species of tree from Canada, where F. simplex cannot survive.
At one point in history Wútóng could well have meant a particular species. It is, after all, listed as one of the six woods in the Tong Guide. In the modern day though it's used in at least three ways:
The people in Shanghai use Wútóng as shorthand for Fàguó Wútóng (法国梧桐, Fàguó = "French") to refer to Platanus × acerifolia, a hybrid tree created in Europe and imported by the French to Shanghai.
People in Northern China use Wútóng as a generic term for multiple varieties of Paulownia-genus trees.
People in Southern China use Wútóng to refer to Firmiana simplex, a tree that grows poorly in northern regions.
More on Tong Woods
Here are 11 names for Tong woods you might encounter:
Báitóng (白桐, "White Tong"), Báihuā tóng (白花桐, "White flower tong") and Báihuā Wútóng (白花梧桐) are all equivalent to Báihuā Pāotóng (白花泡桐), which is Paulownia fortunei.
Fàguó Wútóng (法国梧桐) 'French Wutong', a tree in Shanghai, refers to Platanus × acerifolia.
Gāng tóng (冈桐), Paulownia tomentosa, also known in Chinese as Zǐhuā tóng (紫花桐) or Rìběn Pāotóng (日本泡桐, "Japanese Paulownia")(3). Ancient texts suggest this could also be a good wood for instruments. It is frequently cited in modern times as prime wood for Japanese Kotos and Korean Gayageum, and is cultivated widely, including in the United States and Turkey(7).
Qīngtóng (青桐), Firmiana simplex, also called Wútóng (梧桐) in some places. Explicitly called out in a few ancient Chinese sources as a poor choice for musical instruments.(5) Mei Han 2013 also references Firmiana platanifolia; this is an accepted synonym for Firmiana simplex. (6)
Yóu tóng (油桐), Vernicia fordii or the "Tung Tree". Its seeds can be used to create Tung oil which is used in some varnishes for musical instruments. I don't have evidence the wood was ever used to construct them.(4)
Soundboard Footnotes and Sources
Chinesezither.net, Soundboard Woods article
Efloras.org, Flora of China database
(*): One source I found claims Mongolian zhengs, possibly Yatgas (雅托葛), have soundboards made of 杨木 or Yáng mù, which one source specifies as Liriodendron tulipifera. I haven't confirmed this elsewhere yet so this lives in the footnotes for now.
(1): Search results for Paulownia names from ThePlantList.org
(2): Text of 侗谱 from Wikisource Chinese, summarized in English by Carol Chang on her website.
(3): 毛泡桐图片 page (badly translated as "Pictures of Hairy Paulownia") on YuHuaGu.com. See names in header next to 别称, "Nicknames". Paulownia trees grow fine hairs on parts of their surface.
(4):Handbook of Materials for String Musical Instruments by Voichita Bucur, Switzerland: Springer, 2016, page 388
(5):One modern source that decries F. simplex as a poor choice for instruments is "古典詩文中的桐樹意象與文化意涵, The Symbol and Cultural Connotation of Phoenix Tree" by Ming-Yi Chou, contained in Volume 32 of the Minghsin Journal, published August 2006.
(6): Referenced on ThePlantList.org
(7): M. Hakan Akyildiz, Hamiyet Sahin Kol (2010)"Some technological properties and uses of paulownia (Paulownia tomentosa Steud.) wood", Journal of Environmental Biology (India), 31 351-355
Unfortunately Cheng 1991 is the only one of my sources to describe the woods used in the backboard. He mentions Mulberry, Elm, Catalpa ovata, Phoebe nanmu (a synonym for Machilus nanmu), and Paulownia. Mulberry and Elm aren't particularly helpful as they could be common names of individual trees, common names for categories of trees, or translations from Chinese. The other two are specific species but I have yet to find good references on their usage or value. Sources only offer descriptions of the plants themselves. That leaves me with these names:
Catalpa ovata, also known as Chinese catalpa, Yellow catalpa and Japanese catalpa.(7) The Chinese character 梓 may refer to it but I doubt that's a specific term.(8)
Phoebe nanmu is cited in Cheng 1991. P. nanmu is possibly confused with another species used in guzheng frames, Phoebe zhennan, as some english references use nánmù (楠木) to refer to P. zhennan (9). Diān nán (滇楠), which could be expanded to Diān nánmù (滇楠木) refers to P. nanmu, and suddenly we're talking in circles (10). Some english-language articles claim one or the other were used in the construction of the Forbidden City, but no article states both were, hightening my suspicion that these woods are confused for each other. Send me an email if you have more sources for me!
All parts of the guzheng affect its sound. That goes for the woods used in its frames and ornamentation as well as the soundboard.
Because the frame also has a lot to do with the look of the instrument, wood choice is many and varied. Below is the list of woods compiled from Carol Chang's work at chinesezither.net. Woods that aren't on this list could certainly be used, but these are the ones you are most likely to encounter. If you can find me proof of other woods being used, ideally with 汉字 or down to the genus and species names, I would be happy to add them!
Before we get into it we have to go over some more vocabulary.
Hóngmù (红木): Literally "Red Wood" it's a generic term used when the particular species isn't important. Entry level instruments are often labeled Hóngmù. Dictionaries translate hongmu as Rosewood or Mahogany. Mahogany is native to the Americas, so I can almost guarantee it's not going to be found in entry-level instruments made in China. As for Rosewood...
Rosewood is an over-used catchall. Officially, "Rosewood" refers to trees in the Dalbergia genus, many of which are used for instrument construction. In actual use, the name "rosewood" has been applied to anything with qualities somewhat similar to a Dalbergia. Over time this has included species in the Pterocarpus, Machaerium, and Dysoxylum genera. Without any other information, the term "Rosewood" can't tell you what type of wood the instrument is actually made of.
Sandalwood: In the English-language guzheng world, "Sandalwood" is used to represent Pterocarpus, Dalbergia, and Bobgunnia species - but actual Sandalwoods, such as those known for their fragrance, are of the Santalum genus. Many countries in Asia and the Pacific have native Sandalwood varieties. China has a few cultivated species, but I do not believe them to be native (11).
Zǐtán (紫檀): Can refer to multiple high-quality woods. If the wood is only listed as "Zitan" it is probably Madagascar Rosewood, Dalbergia baroni, or East Indian Rosewood, Dalbergia latifolia. It also makes up part of the name of the highly prized Red Sander, Pterocarpus santalinus (Xiǎoyè zǐtán) and the highly illegal Brazilian Rosewood, Dalbergia nigra (Bāxī zǐtán), but I would expect Brazilian Rosewood to be highlighted if it was used in an instrument. See their entries below for more details.
(11) "SANTALACEAE" by Xia Nianhe (夏念和) and Michael G. Gilbert, Flora of China Volume 5, p 208-219. 2003.
Movable bridges are made of hard woods with a high density as this transmits the sound better. Each wood transmits sounds slightly differently allowing for a range of effects to the timbre. Dalbergia species are the most common. I've seen bridges advertised as being made of unidentified hardwoods, unidentified rosewood, African Blackwood, Thailand Rosewood, and Zitan wood, the last three of which are all Dalbergia species (see below). As a point of price comparison, if generic hardwood bridges retail for $X then generic rosewood go for about $2X, and African Blackwood bridges cost about $3X. The precious woods jump in price both because of the wood and because the string rest material is often more expensive as well. A brief survey on Chinese online marketplace finds high-end bridges are sold for as much as $24X the cost of a generic bridge set.
There are mentions of bridges made of ivory or jade though I have not found definitive sources. There are modern day efforts to perfect hollow ceramic bridges, and I've seen low-end instruments with plastic ones, but wood remains he most common.
There are at least 3 woods used in soundboards, 2 others used in backboards, and 16 woods used in guzheng frames. Each of the woods lends a different tone to the instrument, descriptions of which you can see on Carol Chang's article.
Each entry starts with an English name, their genus and species, their actual Chinese names, and their pinyin. When a wood species has multiple English names I create an entry for each. Entries with "" are improper synonyms or the semi-literal translation of their Chinese name. I've also included three other pieces of information: First, a ranking to give a general sense of which woods are used on more highly-valued instruments. 1 indicates use on entry-level instrument. Woods with a 5 are used for fancy, high-quality instruments. It's possible a higher-quality wood could be used at a lower level, but I'd expect the specific piece used was of a lower quality in some way or had been mislabeled.
Second, I've included the wood's status on the International Union for the Conservation of Nature's Red List of Threatened Species or the Catalogue of Life. Not all woods are on this list, but many are.
Third, I've included the wood's status on the "Convention on International Trade in Endangered Species" (CITES) if it is listed. If a wood is listed on CITES it requires extra paperwork to cross international borders. Products made of one species in particular, Brazilian Rosewood, Dalberia nigra is not allowed to cross borders, period. The technical details are available on the US Fish and Wildlife Service website. For the significance of these listings, see the Issues page. All Dalbergia species are in CITES. Dalbergia nigra: CITES Appendix I, (heavily restricted). All other Dalbergia: Appendix II (commercial restrictions).