D'Addario Violin Rosin Case: 2004 - Tres Design This is a simple case for violin rosin. We designed it so the rosin cake could be rotated as it was worn down, so you wouldnít end up with and enormous crevice and 2 unusable peaks of rosin. The body of the box is 1 piece, with a living hinge and all you do to open it is squeeze the sides. Itís really cheap, but thatís what itís meant to be.