There is formaldehyde when the golden iron frame of the new house turns black. Formaldehyde is a common indoor harmful gas, which is often used to manufacture or process furniture, building materials and other products. When decorating a new house, if the materials used contain formaldehyde, it will gradually release this harmful gas. If the surface of the metal frame comes into contact with the material that releases formaldehyde, it will absorb formaldehyde and have a chemical reaction to make it black, so there is formaldehyde when the metal frame paints the new house black.