Violin rosin has been used to draw sound from the violin since the first instruments were carved from wood hundreds of years ago. Historically, rosin has been made from pine resin, a natural substance found in trees. Many different companies manufacture rosin, and each variety tends to have different characteristics that affect the sound — shading the tone toward bright or dark, and adding varying degrees of “grittiness” to the feel and sound. Further, choosing the “right” rosin is largely a matter of personal preference. Although it functions well most of the time, pine resin does have some limitations — it can crystallize in the cold, damage the varnish on the violin if left to sit, and often cracks or even shatters rather easily. Also, pine resin is an allergen for some, and can cause sneezing and watery eyes during playing in susceptible people.
Supersensitive Clarity Rosin for Violin and Viola is the first synthetic rosin I have seen that is a viable replacement for pine resin. Formulated to by hypo-allergenic, it does not damage varnish. Further, it is not affected by humidity nor does it absorb moisture, which helps it keep its tackiness without cracking in all seasons. But, most importantly, this rosin actually works nicely — and, when played, seems indistinguishable from ordinary rosin (although its characteristics must be evaluated by the individual player). Using my setup, this rosin produced a smooth tone without much grit and nice clarity. However, every player has different preferences in feel and sound of rosin so no single brand is likely to suit every taste.
As a teacher, I have noticed that many of my younger students enjoy handling and applying rosin to the bow, and so the fact that clarity rosin comes in colors (pink, red, blue, green, and purple) gives it a modern look that is especially appealing to youngsters. Also, young students are more likely to over-apply rosin and also not to wipe the instrument clean as frequently as necessary to prevent ordinary rosin from damaging the finish. Thus, this colorful rosin can also help extend the life of the instrument.
Though I have not found a synthetic substitute for horse hair (or for my wood violins for that matter) that functions as well as the original, this rosin does appear to be a viable substitute for pine resin, and one that adds a little fun and color into the mix as well.