The Oil Can finish is a unique hot oil oxide process applied to the wedge that will wear off over time, leaving a raw finish. There is some variation in finish with Oil Can and this has always been desirable as each part looks and wears differently.  As this finish wears off, the raw finish will be subject to rust.  If you want to try and preserve your finish longer, you can apply a thin coat of baby oil and make sure that you dry and clean the wedge after you play.  Many players do like the rusty look and they believe it imparts more spin to their shots.