This substance is a natural byproduct of copper mining. It is a black, odorless solid that is stable in the air. Other names for this substance include tenorite or cupric oxide. It is not flammable, but it is harmful to humans if ingested. It cannot be mixed in water, but it will dissolve in ammonium chloride. Copper oxide is mostly used as a precursor for various copper-related chemicals and substances. Many wood preservatives are created by mixing copper oxide with other substances. In ceramics, this material is utilized as a pigment, creating colors such as blue, red, and green. Because it is stable in the air, copper oxide does not have to be sealed. However, it should be handled with gloves to prevent irritation to the skin. Direct contact with the eyes can be harmful, and it should not be ingested for any reason.