For many centuries, strings used for the harp and similar instruments were made from animal tendons. Thinner tendons were used for high notes, while thicker tendons were used for low notes. Later, the strings were coated to increase their mass. The first "wound" strings were not actually wrapped around each other but rather intertwined. In the 14th century, the first metal strings were constructed using brass or iron. Initially, only a few gauges were available, and all were cold-drawn. It was not possible to wind a metal wire around a core until the end of the 18th century, and the windings were not as tightly packed as they are today but rather in open loops. When hot-drawing of metal wire became possible, a wider range of gauges became available. Today, the high-quality wire used is made of high-grade steel (for more information, refer to the chapter on Materials Science). Only toward the end of the 18th century did the first three-string unison choirs appear. When restoring historical instruments, it is not advisable to use modern wire: specific types and gauges must be ordered from a qualified supplier.

To produce high-quality piano strings, it is important to strictly adhere to these production standards:

• Carefully select raw materials.
• Use chemically clean material derived from special melting procedures.
• Perform high-quality drawing of the base material to achieve a homogeneous piano string without defects or surface imperfections.
• Professionally supervise production, including factors such as wire speed in relation to wire thickness, temperature in the acid bath, wire dwell time, wire cooling, and machine lubrication.
• Continuously monitor production and perform precise final control of all measurable wire characteristics such as hardness, surface, elasticity, and homogeneity.

Wire produced according to these high production standards can be defined as piano wire. The base material at the beginning of this process is in the form of cast bars that are drawn into a 5.5 mm thick wire. This wire is then heated to 900°C and rapidly cooled to 500°C in molten lead or salt. During the heating, hardening, and stretching process, waste products are created and chemically removed. Subsequently, the wire is lubricated to preserve it during the stretching process. The wire is drawn through the machine, thinning and elongating it. It is important for the gears of these machines to be perfectly synchronized with the increased wire passage speed.

For both upright and grand pianos, it is advisable to use three bare strings per unison in the treble range. As for the bass strings, they should have a copper winding. In the case of double-wound bass strings, both the first and second windings should be made of copper. The winding should be done in such a way that all ends of the copper windings align with their respective points on the bridge. The length of bare string between the end of the copper winding and the bridge, as well as between the end of the copper winding and the nut, should not exceed 15 mm. In double-wound strings, the outer winding should be oriented in the opposite direction to the inner winding. The copper wire should adhere well to the steel core of the string to avoid buzzing or tonal defects in the sound. Additionally, the copper wire should not be oxidized or corroded in any way.