There is quite a discussion of rosin and its use, the pros and cons of different brands, etc. at this forum click

The discussion includes this comment " The Nymans has a tendency to glaze the hair , particularly in warmer situations, so that it will eventually create a slippage of the bow on the strings no matter how much rosin is applied. Kolstein's actually functions better in warmer situations and will almost rejuvenate itself when the hair or strings become heated, due to friction of playing. Just keep in mind most rosins are not compatable with each other and for best results, it is always prefered to have fresh hair with the change of a rosin. If this is not feasable, the best thing is to practice for a day or two not using any rosin. This will allow the hair to empty itself of residual build-up of accumulated rosin and hopefully allow the new rosin to impregnate the hair, not just sit on top of old rosin. Any addition questions on Kolstein rosin or rosin in general, I will be most happy to answer. I have been involved in rosin making for over 25 years and feel we have a great deal of input to offer on the subject. -Barrie Kolstein"

Again, the entire discussion on rosin is at Rosin

alice