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How do overtones affect the tone color of a stringed instrument?

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Koto — stringed instrument A Japanese musician plucking the strings of a koto with the right hand to generate a pitch and pressing the strings with the left hand to alter the tone.

Overtones, also known as harmonics, are fundamental to the timbre—or characteristic tone color—of a stringed instrument. While a vibrating string produces a fundamental pitch, it simultaneously vibrates in segments to create these additional frequencies. The specific combination, presence, and relative intensity of these overtones determine the instrument's unique sound quality.123

Several factors influence which overtones are emphasized, thereby shaping the instrument's timbre:

Resonator Design: The size, shape, and material of the instrument's body and soundboard act as a filter, amplifying certain overtones while suppressing others.2
Excitation Method: How a string is set into motion significantly alters the overtone spectrum. For example, plucking a string with a sharp point emphasizes higher overtones, resulting in a "bright" tone, whereas using a soft pad, like a piano hammer, emphasizes the fundamental pitch.2
Playing Technique: On many instruments, the player can influence tone color by choosing where along the string to pluck, strike, or bow.2
Sympathetic Vibration: The use of sympathetic strings—which vibrate in response to the main strings—reinforces specific upper harmonics, often creating a bright or silvery quality.2