The Melos Cello Dark Rosin is tested to function effectively under any condition, for every single instrument.
That's why for every instrument are two different types of rosins, 'light' & 'dark'. The 'light' type is used more in high temperatures (spring or summer), for 'smooth' playing or for solo in chamber music.
The 'dark' type is used more in low temperatures (autumn or winter), for full-tone playing, in an orchestra, or for solo in great concerts. It depends also on the art of the musicians playing.