I have played a six course lute double-fretted, single strand of fret going around the neck twice, with the fretting carefully selected and tied by the lute's maker Ray Nurse, for many years. The gut frets, with all gut strings on the lute, has lasted so well that I have only had to have the instrument refretted once in 12 years of continuous use of the lute. The very slight and gentle "fizz" on the sound of the fretted notes is attractive to me and characteristic of the sound of this lute. I think Capirola even refers to this effect in his instructions.
The key thing seems to be to have a very low action, a low nut, and very thin diameters for the double frets. They grade minimally from down the neck. Double fretting is frequent in depictions in paintings and prints throughout the sixteenth century and well into the seventeenth century. It even occurs in Laurent de la Hyre's Allegory of Music (Metropolitan Museum of Art) theorbe player. I also enjoy single frets which I have on my other two six course lutes. Kenneth Be -- To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
