The type of material used for strings controls their timbre. Different materials have been used for traditional guzheng over the centuries, each with different pros and cons. Modern instruments are usually strung with a multi-part string. Typically referred to as "Nylon", these modern strings have a core of drawn steel, wound with copper in the bass strings, which are then wound with a tight thread which is then wound in nylon. The ends are then wound in an additional layer of thread. It's easier just to say "Nylon". These strings are the most common because:
- Relatively cheap to make
- Can be made of consistent quality
- Durable, Break less often
- Are more comfortable to play
- Have a well-rounded sound
- Can be held at a higher tension, producing a louder sound and allowing for faster play styles.
Compare that with the other materials:
Effectively the core of the modern string, drawn wire strings were made of steel, steel wound in copper, straight copper, or brass. Metal strings are more durable than silk, easier to produce consistently, and louder. Their timbre is described as bright, at times emphasizing higher frequencies that can be unpleasant to the listener. They can be painful to play and do not transmit the nuance of left-handed techniques as well as silk. Keeping the tension low can help, but prevents the instrument from being used for modern, faster songs. Sources: Cheng 1991, Han 2013
Silk was considered one of the best materials for strings for a very long time. It transmits nuances that metal and nylon strings do not capture, most noticeable in left-handed techniques. There is a strong historical and cultural sense to the material thanks to China's history with silk. Silk strings are expensive, however, and prone to breaking with improper technique. They were kept at a lower tension than modern strings in order to emphasize those slower nuances and required frequent tuning. This prevents silk from being used for faster, louder play styles. Compared to metal-stringed instruments like the piano, the silk strings are said to have a 'dull' tone. Sources: Cheng 1991, Han 2013
While rarely discussed in English sources, strings were likely made from additional materials at different points across the millennia. The guzheng manufacturer Tianyi published an overview referencing animal hair and animal "tendon" being used as strings:
The zither string has gone through several stages in its history. Early on strings were made of dried deer tendon [species: Cervus elaphus] or hair from the deer's tail. The advantage of these types of strings is their soft, pleasant sound. The disadvantage is their small volume, (易走音?), and their [short] service life.
There are regional clues to this as well; Carole Pegg writes in The New Grove Dictionary of Music and Musicians that the Mongolian zither the yatga is said to have had strings made from a variety of materials including horse hair and animal intestine (referred to in the west as catgut). It is perfectly possible that Chinese zithers were strung with such materials at some point and place in time.
One questions that comes up from time to time is what thickness of string is appropriate for which location on the instrument. This is especially important when people are trying to replace a broken string on an older guzheng with drawn wires. There is no universal standard as to what thickness of string should be used at which point on an instrument, but there are some general trends observable on modern instruments. Below are the thicknesses of strings on 8 different guzheng, ranging from steel to wound copper to nylon. Guzheng A-D are 21-string guzheng with modern nylon strings. The first two are full size, the last two are travel size.The remaining Guzheng E-H are drawn-wire guzheng, strung with steel or copper-wound steel.
- All measurements were taken in inches. The second chart has the same measurements converted to millimeters.
- The 16-string guzheng used far thinner wires than the 18-string.
- The sudden jumps in thickness around strings 14+ are from the addition of copper windings.
Wire is sold by its "gauge" but there are several competing measurement systems. Conversions from measured diameter to gauge can be found here.
Guzheng String Diameters, Inches
Guzheng String Diameters, Millimeters
Modern strings last for different lengths of time depending on how much they are played, how they are tuned, and how energetically they are struck. The brand TianYi suggests in their knowledge base that for someone who practices everyday for 1 hour, strings will last for 2 years. Carol Chang meanwhile suggests that the thinner, higher-pitched strings last 6-12 months, while the thicker bass strings can last more than 2 years.
The real deciding factor is your preference for the sound. Over time the string materials wear out. The timbre of their sound changes. You'll be able to get them to a desired pitch, but the extra qualities that make guzheng music so special will alter. If the sound doesn't bother you there is no need to change strings. I know guzheng players and teachers who only change strings when they break.
Let's get a fear out of the way: yes strings can break, but they are unlikely to hurt the player or the instrument. The wire in the center is typically what fails as it carries the tension. When it can no longer sustain the tension the nylon wrapping takes over, stretching and loosening. It may startle you but it won't hurt you.
Tension and striking force are what wear strings out. Over tightening strings wear them out faster. If, when tuning, you change the pitch of the strings drastically without lifting the strings up to equalize their tension, that local tension buildup will weaken the string, leading to it failing sooner. Some, especially the treble strings, can break right then.
To avoid these issues, follow the guidelines for tuning and check the charts for bridge placement for each key. If your bridges are close to those locations and you are using the correct string for each space on the guzheng, your strings won't be too tight. If your bridges are way far to the left, towards the tail, that's a sign your tensions will be too high to compensate.
Last thing to consider is that every brand and quality level of string is different. Each set can have a different timbre, and last a different length of time. The lifespans given above are benchmarks. Your mileage may vary. If multiple strings break while playing and it's been a few months since you last bought new strings, consider getting some replacements. If the strngs are new, it's a sign the instrument is at too high of a tension or is being mishandled in some way.