Single .18 gut string for Bass (Tenor) Viol da Gamba.
Fundamentally even today it is still possible to use plain gut strings for the lowest strings of the gamba, however the stiffness and thickness of the mono-filament of the gut string is a considerable impairment to playability of the deeper notes.
It is only since 1660 that spinning with copper has evolved. However, the most popular winding is silver-plated copper wire, which has the advantage of the silver coating combined with the sound quality of the copper string.
For studio takes we recommend silver wound gut string with a polished surface. They are quiet even as your fingers change position on the fingerboard. However, it has only been possible to manufacture this sort of string since the 20th century.