Hidersine Cello Rosin 6C 1098. 'Hidersine Cello 6C' Rosin, cloth mounted and boxed. Rosin is a natural product made from the resin secreted by fir and pine trees. The resin is heated and mixed with oil and other ingredients, then cooled and allowed to solidify in the now familiar cake form. The carefully guarded recipes vary considerably and are carefully formulated to suit different types of strings and playing styles. If you are playing on metal strings, choose a hard rosin; for synthetic strings we would suggest a medium rosin; for gut strings a softer, stickier rosin is more effective.