The minute one puts on a new set of violin strings, they begin to break down! Sad as that may seem, a comforting point is that well made strings can last a long time and the decay, is very, very gradual.
While of course we always urge our customer/players to wipe their strings off after each session, that all too often is not enough to keep off the grime and/or hand acidity that builds up on the string, often not even discernable by just looking at them with the naked eye. Trust me, if you have had your strings on for even a month AND you are religiously wiping them clean each time, there are a couple of techniques you can use that can and will bring old strings ‘back’.
First, if your strings seem to look a little cloudy or dull, try using a swab of rubbing alcohol. BE VERY CAREFUL not to drip any alcohol on your violin’s varnish. (We suggest that you simply take a dry dish or face towel and slide in under your fingerboard laying it on the violin bell all the way up to the top of the bridge. This way, if you accidentally drip, it will drop on the towel. BTW, less is more here! Just a dab of alcohol with a paper towel pinching the string, up and down. If your string is really dirty or rosiny, just take an other swab of paper towel and do this process once or twice.
Now, if your strings are REALLY beyond help (yes, really gross!) you can first take some extra fine steel wool, without any chemical on it and by pinching the string, sliding up and down, will bring that string to look brand new! Yes, it might still be old and worn, but if your strings are dirty enough, you will and should see and hear a noticeable difference in how much better they respond than just before you did the cleaning.
Sometimes applying a very small (dot) of Vaseline in the steel wool will clean and not dig too much into that string, while really clean it! Where to buy this steel wool? Home Depot or any paint or hardware store. Look for the 5 zeros on the package! Do not use anything more course than that.
Lastly, you can be safe and repeat the alcohol wiping again to be sure now oil or Vaseline remains in the string (and gets in your bow hair). Even a dry towel will do fine to wipe off before playing with your bow.
Lastly, get some new strings! This (cleaning) will only fix part of the problem and not remove the hours and months you’ve played them for.