I spent ten minutes applying a new cake of Bernardel Rosin for violin, viola, and cello into the hair of my Lothar Seifert German bow. Then I spent a half-hour doing long-tone exercises that Gary Karr showed me one summer while he taught at Indiana University, and later at The Hartt School.
A few months ago, Jacob Bradford (a luthier in Fountain Inn, South Carolina who performs repairs on violins, violas, cellos, and basses) carved a new bridge using a Despiau bridge blank and repositioned the sound post for a bright sound. The results improved the sound quality, playability, nuanced responsiveness when soloing on my 140-year-old August Heck double bass.
This Bernardel Rosin worked well for "concerto sound" long-note bowing.