When were the first metal strings made for musical instruments?

Question:

When were the first metal strings made for musical instruments?

Answer:

Brass wire had been available before steel one, but the popularity of metal
wire as strings for musical instruments really started with an invention of
piano wire at the industrial revolution.

Early 19th century Martin guitars strung with high tension steel strings
(some steel wound strings exert as much as 15kg per string of tension).

The first public performance of a Hawaiian steel guitar was in 1886.

Martin guitars started to make steel string guitars as custom order in early
1900. As early as 1903, Gibson guitars adopted steel strings to their
arch-top guitar, like L-O model.

Steel string guitars gained popularity in 1920's and 30's.