Copper and bronze react with oxygen, which results in a distinctive patina. This coating, which is oxidized copper, protects the underlying material against corrosion but leaves all other characteristics unchanged. Patina is a layer of oxidization that you will find on antiques. Think of a new penny with no patina and an old penny with a layer of patina depending on how old it is.
Some owners like the patina as it forms differently depending on its environment and makes the pencil unique to its owner. Others prefer the shiny, new look -- if that’s you, I recommend either choosing the stainless steel or titanium or keep your copper or bronze pencil looking brand new by using the included Scotch Brite pad.