How do you oxidize copper to black

Mix one part yellow sulfur powder and at least five parts Vaseline into a paste. Store the paste in a glass container. Coat the copper item with a thin paste film and leave it until it attains the desired tarnish. Wash off the paste with gasoline [source: Metal Detecting World]. Hydrochloric acid- Hydrochloric acid is very strong and used in products meant to clean bathroom tiles and sinks, etc. This one is not often recommended to clean copper as it is very harsh and sometimes may even damage the utensil. Copper oxide acts as a weak base because when dissolved in water, it produces mild basic hydroxide Cu (OH)2. Since copper (II) oxide is a metallic oxide, it is basic. -When CuO is in an aqueous solution, it does not dissociate completely, meaning it is a weak base. Also, it forms copper hydroxide (Cu(OH)2) when dissolved in water. Other metals, such as bronze and copper, also undergo oxidation, leading to corrosion. So, the answer is NO; copper does not rust. While CuO is considered relatively insoluble in water, only low levels (µg/L) of free Cu ions are needed to provide significant toxicity to aquatic and plant life. Copper corrodes by oxidation, which reacts with oxygen in the air to make oxide. Oxide then combines with CO2 to form copper carbonate, which gives it a green colour. Copper forms a green deposit on its surface when exposed to air, typically a mix of copper carbonate and copper hydroxide. If you are looking for high quality, high purity and cost-effective copper oxide, or if you require the latest price of copper oxide, please feel free to email contact mis-asia.