1977 Georg Bolin Comes 11-string Alto Guitar natural

Very Good condition, 7,5/10, Made in Sweden, including original hardcase with red interior, smaller body with cutaway, spruce top and beautiful rosewood body, 11 strings (7 normal plus 4 bass strings), dated on the label Stockholm 15.12.1977, the strings are a bit rusty, more info from Wikipedia: The eleven-string alto guitar (also known as altgitarr, archguitar, or Bolin guitar) is an extended-range classical guitar developed by Swedish luthier Georg Bolin in the 1960s.

Original Bolin instruments are now rare and valuable.[1] The Bolin alto guitar most often has eleven strings, but Bolin also made a thirteen-string version.

The 11-string alto guitar is a multi-string classical guitar, which generally refers to classical guitars with more than six strings. Classical guitars with extra strings can have from seven to 13 or more strings.[2] However, an 11-string is the most useful for performing lute music, particularly Bach and Weiss. The first six strings are tuned in the same intervals as the normal classic guitar. Therefore, a musician can play with conventional fingering on those strings.History
Georg Bolin first constructed 11-string alto guitar with collaboration with Swedish guitarist Per-Olof Johnson in the 1960s. Johnson is the teacher of a well-known guitarist Göran Söllscher who made this instrument famous through his extensive usage of Bolin's 11-string alto guitar.[4][5]

Johnson was fond of lute music, but the difference in playing techniques between guitar and lute is significant, and he was looking for a way to play lute music using guitar playing technique. Thus, the design goal was specifically to allow guitarists to play renaissance lute music.

This design introduced two main elements. The first was to provide conventional lute tuning by tuning the first six strings a minor third higher (hence the name "alto guitar"). It is equivalent to putting a capo on the third fret of the normal prime guitar. The second element was to add five extra strings to accommodate low notes.

Tuning
The typical 11-string alto guitar tuning is (from low to high strings): Bb1 C2 D2 Eb2 F2 G2 C3 F3 Bb3 D4 G4.[6]