HOMEZY Water Bottles Are Made From 100% Pure Copper and Oxidation as a Sign of Purity. A natural oxidation process that occurs with every pure copper bottle. It's indeed true that copper can form an oxide layer when exposed to air and water. Copper Does Not Rust the Interesting Black/grey/green Spots That Will Develop on the Surface is a Layer of Oxide That Forms to Prevent Further Corrosion. Contrary to Misconceptions a Well-oxidized Copper Surface Can Actually Signify the Purity and Authenticity of the Material.Cleaning your bottle is effortless you can clean it by just using lemon and salt.We recommend that it would be great if you embrace the true nature of copper as It Enhances the Bottle's Character and Does Not Compromise Its Functionality. Enjoy the Health Benefits and Timeless Beauty of Your Copper Bottle Knowing That Oxidation is an Inherent Aspect of Copper's Nature.