Cleaning Solvents
We see lots of Internet Advice™ on how to remove excess rosin from gut strings: rubbed down with alcohol, soaking in mineral spirits, scraped with sandpaper or steel wool, wiping down with lemon juice, rubbed with olive oil-soaked licorice(?), placed in an oven(?!?), and on, and on.
It is NOT recommended to use liquid solvents on gut strings, as it will cause the collagen to physically break down reducing the lifespan of the string (and even damage the varnish of an instrument).
How Do I Remove a Buildup of Rosin On My Strings?
The simplest, most effective method for removing excess rosin is to wipe off the strings with a soft, dry cotton or microfiber cloth after each playing
But, the above being said, if you insist on using chemicals — versus just cleaning the strings with a soft cloth regularly — the best way to remove rosin buildup on strings is with denatured alcohol. This will remove the rosin and leave no residue on the string. Remember to use an almost-dry cloth to avoid dripping on the instrument or soaking the string, and be sure to keep a dry barrier cloth between the string and the instrument. Removing a little at a time is the best way to go.