Cecilia Rosin Spreader

This is a rosin spreader from Cecilia, a rosin manufacturer in the United States.

In Europe and America, it is becoming a trend not only to apply rosin but also to use a rosin spreader to evenly distribute it on the bow hair. Depending on bow pressure and playing technique, the rosin-coated side of the bow hair may not always be the only part in contact with the strings. Using a rosin spreader to evenly spread the rosin to the back of the bow hair allows for stable contact regardless of playing technique.
If you are interested, please search for Rosin spreader.

Although originally developed to evenly distribute rosin for violins, violas, and cellos, it is also effective for double basses.
When using high-viscosity rosin, such as for pop music, clumps can form on the bow hair. However, the rosin spreader can eliminate these clumps and disperse the rosin without damaging the bow hair.