The melonite finish on the M&P gets a bit dull after a while. I think the dullness is from muzzle blast, dust in the atmosphere, or whatever. Anything that touches the pistol will "polish" that point. Every once in a while I wipe down the exterior of the slide with a silicon impregnated cloth (MidwayUSA Silicone Impregnated Gun Cleaning Cloth) It does a great job on all the metal surfaces, just don't use it on the grip or any part you don't want slippery.