You will find that with use; the Copper product will patina. That is completely normal (and natural!) and the best way to clean it and restore it to its natural shine is to wipe down with lemon juice and water and wash it with copper cleansing powder. For further ease and assistance we provide a complimentary sample of Copper Cleansing Powder (By Pitambri), this powder acts as an agent in restoring the original luminous texture of the product. The reason for sudden color change in a copper utensil or a pot is because copper does not react with water but it does react with atmospheric oxygen to form a layer of brown-black copper oxide (refer to the picture, suggesting nonoxidized copper on the left and oxidized copper on the right) which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion. Thankfully it is not permanent and can be removed, polishing copper utensils take up a little elbow grease but drinking water from copper utensils gives amazing health benefits like fighting cancer, acts as an anti-aging agent, is full of oxidants, lowering the risk of heart diseases and hypertension, helps in better functioning of the digestive system, protection against infections, beating anemia, etc.