However, if it is not properly kept, high-purity gold bars, coins and gold jewelry will still change color. This has a lot to do with collection and maintenance methods. People have the impression that gold is relatively stable in nature and difficult to be corroded. Why do high-purity gold bars change color? Experts from the Gold and Jewelry Quality Testing Center of Hangzhou Quality Inspection Institute said that although the purity of thousands of gold has reached 99.9%, gold still contains some other metal components such as silver, copper, iron and zinc. When these metals are oxidized or react with other chemicals, some compounds will precipitate, which looks like gold has changed color. According to the Gold Jewelry Quality Testing Center, they often encounter discoloration of gold bars, coins and gold jewelry. For example, there are rust spots on gold bars and gold turns white and black. Black is due to the chemical reaction between copper and silver contained in gold bars, resulting in copper sulfide and silver chloride, while white is due to the contact between gold and mercury vapor. Once a consumer went to the hospital wearing gold jewelry and accidentally broke the body temperature agent. As a result, the jewelry turned white after contact with mercury. Now there are more and more people who store physical gold at home. Gold jewelry experts suggest that gold should be stored in a dry place away from light and away from polluted rooms such as kitchens and bathrooms. In addition, although the weather in Hangzhou is humid, the place where gold is stored does not need to be deliberately moistureproof, because the moistureproof agent is volatile and prone to chemical reactions after contact with gold. Some ladies are used to putting gold ornaments and cosmetics together, and the chemicals volatilized from cosmetics can also lead to the discoloration of gold ornaments.