Not new, but it can turn out pretty good. Just go to Home Depot and get some of the ...sulfuric? acid. Can't remember which one it is that they carry for cleaning grout and tile and such. Paint some on (using gloves and eye protection at least) and wash off with loads of water. Will make a big difference, but hard to tell how much.
Dilute the acid with distilled water and start off with a 10% solution if you are going this way. Be patient and gradually increase the solution strength. Also have a box of backing soda on standby to stop the reaction along with a bucket full of water to quickly rinse off the part and eye protection.
Guess who use to teach chemistry in a former life.