Gismonti himself uses a unique technique: soft flesh of the thumb for bass (to sound like a warm double bass) and nail for the melody (to sound like a flute). In the duo, Guitar II should use purely rest strokes (apoyando) on the bass. Guitar I should use free strokes (tirando) with lots of finger surface area.
If you are searching for the "Água e Vinho" guitar duo PDF, do not look for it merely as a technical exercise. Do not look at it as a series of frets and strings. agua e vinho guitar duo pdf