Using Rosin Rosin is applied by drawing the bow across the cake as if playing a string. Although many players, especially fiddlers, may wish to give certain areas of the bow hair more attention, in general it should be applied with long smooth strokes to give a uniform covering. Avoid applying too much; a thin layer is better. After playing the excess rosin should be removed from the bow with a soft, dry cloth. Rosin is the purified form of the natural resin secreted by fir and pine trees. This is then heated and mixed with oil and other ingredients according to carefully guarded recipes. The mixture is then cooled and allowed to solidify in the now familiar cake form. These recipes vary considerably and are carefully formulated to suit different types of strings and playing styles.