<P> A wide range of chemicals, both household and commercial, can give a variety of patinas . They are often used by artists as surface embellishments either for color, texture, or both . Patination composition varies with the reacted elements and these will determine the color of the patina . For copper alloys, such as bronze, exposure to chlorides leads to green, while sulfur compounds (such as "liver of sulfur") tend to brown . The basic palette for patinas on copper alloys includes chemicals like ammonium sulfide (blue - black), liver of sulfur (brown - black), cupric nitrate (blue - green) and ferric nitrate (yellow - brown). For artworks, patination is often deliberately accelerated by applying chemicals with heat . Colors range from matte sandstone yellow to deep blues, greens, whites, reds and various blacks . Some patina colors are achieved by the mixing of colors from the reaction with the metal surface with pigments added to the chemicals . Sometimes the surface is enhanced by waxing, oiling, or other types of lacquers or clear - coats . More simply, the French sculptor Auguste Rodin used to instruct assistants at his studio to urinate over bronzes stored in the outside yard . A patina can be produced on copper by the application of vinegar (acetic acid). This patina is water - soluble and will not last on the outside of a building like a "true" patina . It is usually used as pigment . </P> <P> Patina is also found on slip rings and commutators . This type of patina is formed by corrosion, what elements the air might hold, residue from the wear of the carbon brush and moisture; thus, the patina needs special conditions to work as intended . </P> <P> Patinas can also be found in woks or other metal baking dishes, which form when properly seasoned . The patina on a wok is a dark coating of oils that have been burned onto it to prevent food sticking and to enhance the flavor of the foods cooked in it . Steaming foods or using soap on a wok or other dishware could damage the patina and possibly allow rust . </P> <P> Knife collectors that own carbon steel blades sometimes force a patina onto the blade to help protect it and give it a more personalized look . This can be done using various chemicals and substances such as muriatic acid, apple cider vinegar, or mustard . It can also be done by sticking the blade into any acidic vegetable or fruit such as an orange or an apple . </P>

Statue of liberty what is patina and why is it not removed