Addendum: Metal and
metal wound strings
Here, I will summarize what I think about metal strings and metal wound based on literature and information on web sites and catalog of string manufacturers. I will update as I get new information.
The first metal string for musical instruments was used in
southern Germany after 14th century. Strings made of iron, copper or
silver seem to be used in these early days. Iron strings were first
mentioned in 1511 and stretched by hand. Regarding strength, early
metal strings seemed to break rather easily. However, string tension
used on the period instruments was low and these metal strings were
strong enough to produce gentle sound on them.
Gut (sheep gut) string were started to be used by those along the Mediterranean in Europe. It was said to be difficult and require special know hows to make long lasting gut strings of uniform thickness. In a period between 18th and early 20th century, metal strings were all the rage, due not only to their brilliant sound and sustain, but also to the improved quality metal strings lasting much longer than gut ones that wear and break easily (therefore, require frequent restringings). The process of producing long lasting gut strings, especially thin gauge ones, was a heavily guarded secret. There might be manufacturers that supplied high quality gut strings steadily at some time. However, I would guess that the quality of gut strings can become inferior when the secret was not transfered in its entirety.
5 different metal known to be used as musical instrument strings by 18th century are gold, silver, copper, iron, and brass. Bronze wire was also used in 17th century and steel wire had been used since 1834. Then, plated and coated wires joined the group and many of them are still produced today. Steel strings tend to have strong but sometime a little rough tone and bronze ones rather soft tone. But tone characteristics and durability of strings change by plating and coating on them. For example, brass wires develop rust even when they were unused.
Metal wire wound strings
"L'Encyclopedie Diderot & D'Alembert" published in 1758 features a print showing a process of producing metal wire wound strings. Therefore, they should have been in use before that, although the materials used were not known. The earlier metal wound used either gut or silk core on which wire is wound. Some (also mentioned in Aquila's web site) said that metal wound strings existed even in mid 1600's. Flexibility of the core material is an important factor on sound of the metal wound strings. To produce these for bass strings, it easy to wind wire on a thick gut core to get necessary density. But the sound of them seemed to be unattractive due to their inflexible characteristics. This had continued till more flexible core material than metal being introduced in the late 17th century.
In the late 17th century, natural silk had been used as core material in medieval Europe. By winding wire on a core of many thin fibers twised togather, the desired flexibility had been achieved rather than using a thick gut core. As a matter of fact, cat line, a rope shaped string, had been invented to achieve the flexibility. At the period, metal wire was wound over a thin bundle of silk fibers under tension by hand, similar to the gut string making process. Processes of producing thin metal wire had established and mass production of them started in late 17th century, also.
Silk cored metal wound strings were hailed by player of the time, but it was difficult to produce very thin strings due to hygroscopic and stretchy nature of silk. After 1946, synthetic fibers like nylon are used for core material and great improvements were achieved on strength, durability, and insusceptibility of humidity and temperature.
While finishing this far, I find a new information on metal strings. I will update these later.