Bronze has a beautiful golden tone similar to 14k yellow gold. The high copper content in brass and bronze can cause it to darken over time. This is primarily due to a reaction to water and humidity. Some people, depending on their personal PH balance, experience a green coloring to the skin when it comes in contact with bronze and brass. This is perfectly harmless and is due to the copper content. If you prefer to avoid the dark patina to the metal, try to keep your bronze and brass as dry as possible.