Classification of gold purity and identification methods

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Gold is a precious metal; it has a high value. Expressions such as \"splendid and magnificent,\" \"genuine gold cannot be weakened by fire,\" and \"there are houses of gold in books\" all reflect the high status that gold holds in people’s minds. To get involved in future gold investments and seize opportunities for value appreciation and preservation in the gold market, it is necessary to understand the properties and characteristics of gold as well as its role in the monetary and financial systems. 　　As a precious metal, gold possesses excellent physical properties, including a high melting point of 1,064.43 degrees Celsius. The saying \"true gold fears no fire\" refers to the fact that gold does not melt easily under ordinary flames. It has a high density of 19.31 grams per cubic centimeter (at 18°C), giving it a heavy feel. It has good toughness and ductility, as well as high electrical conductivity. Pure gold has a bright yellow color, but its hue changes significantly when other metals are mixed in; for example, gold-copper alloys are dark red, while those containing silver are light yellow or grayish-white. Gold can be ground into powder, which is why gold appears in a dispersed state in nature. Pure gold jewelry can also wear down over time, resulting in a decrease in its weight. 　　Due to its characteristics such as difficulty in extraction, high mining costs, and excellent physical properties, gold has not only been used by humans as an ornament throughout history but has also been given a monetary value over time. It was not until the 1970s that gold was separated from its direct monetary function, that is, gold was demonetized. But as a precious metal, gold remains the world’s main international reserve. According to the gold reserves data published in 2000, the top 10 countries and international institutions in terms of global gold reserves are: the United States (8,137 tons), Germany (3,469 tons), the International Monetary Fund (3,217 tons), France (3,025 tons), Switzerland (2,494 tons), Italy (2,452 tons), the Netherlands (912 tons), Japan (764 tons), European banks (747 tons), and Poland (607 tons). The United Kingdom ranks 11th with 538 tons, while China is in 14th place with 395 tons. 　　Based on their properties, gold can be divided into two main categories: raw gold and refined gold. Raw gold is also known as “prime gold,” “natural gold,” or “unrefined gold”; it is gold that has been extracted from mines or riverbeds and has not yet been refined. Gold that has been refined is called \"refined gold\". In refined gold, the color of gold changes due to the addition of other elements. Gold to which only silver has been added, with no other metals present, is generally referred to as \"pure-colored gold,\" while gold that contains both silver and other metals is called \"mixed-colored gold.\" K gold is a way of indicating the purity of alloyed gold; 4.1666% gold content corresponds to 1K. Gold can be denoted by its karat value, such as 24K, 22K, 20K, and 18K. 24K gold has a gold content of 99.998%, and is essentially considered pure gold, while 22K gold has a gold content of 91.665%. The purity of gold can also be expressed as a percentage by weight; it is typically represented by dividing the weight of the gold into 1000 parts. For example, a gold piece marked as 9999 has a purity of 99.99%, while one marked as 586 has a purity of 58.6%. 　　There are two types of purity markings for gold products in the market: one is in percentage form, such as G999, etc ； Another type is gold-plated metal, such as G24K, G22K, and G14K, etc. Our country has regulations regarding the markings and labels on gold products; generally, it is required that there be the manufacturer’s code, the name of the material, and the indication of the purity content, etc. Products without such markings are considered defective. The same is true internationally. However, for some particularly small products, it is also allowed to leave them unmarked. 　　Gold jewelry refers to jewelry made primarily from gold. The chemical symbol for gold is Au; its density is 17.4, and its Mohs hardness is 2.5. Based on their gold content, gold jewelry can be divided into two categories: pure gold and K-gold. Pure gold jewelry has a gold content of over 99%, with a maximum of 99.99%. Thus, it is also known as “99% gold,” “pure gold,” and “red gold.” 　K-gold jewelry is made by adding other metals such as silver or copper to gold, and is also known as \"mixed gold\" or \"graded gold\". Due to the varying amounts of other metals added, different K values for K-gold jewelry are created. 　Among gold jewelry, pure gold pieces are relatively soft; they leave marks when bitten, are prone to bending, and have a golden color. Pure, gentle, with a heavy feel – it has a substantial texture. K-gold jewelry is slightly hard; it does not leave marks when bitten. Its color is yellow with a hint of white, and as the K value decreases, the white component increases while the yellow component decreases. 18K gold jewelry doesn’t feel as heavy as pure gold jewelry. Furthermore, both pure gold and K-gold jewelry bear markings; on gold jewelry, these markings may use the character for \"gold\" or the English letter \"kg\". The corresponding K value is indicated; in addition, the jewelry also bears stamps indicating the place of origin from different manufacturers. 　Gilded jewelry is made by applying a layer of gold onto the surface of other metal jewelry using electroplating; its color is similar to that of genuine gold jewelry, featuring a golden luster, making it difficult to distinguish from real gold jewelry in recent times. However, gilded jewelry feels lighter and more delicate, is harder in texture, leaves no marks when bitten, and tends to fade over time. Some poorly plated gold jewelry has a color that is either red, white, or mottled. 　Plated jewelry refers to items whose surfaces are covered with 24K or 22K gold leaf; if the karat value of the gold leaf is too low, its flexibility is reduced. Plated jewelry looks similar to genuine gold jewelry, with a shiny golden appearance and it does not fade easily, making it difficult to distinguish between the two. However, upon close inspection of the recessed areas, corners, and the back side of the jewelry, it can be seen that the gold foil is uneven, with edges lifting and peeling. If there are broken joints on the jewelry, the cross-section of the metal material can be seen here, appearing yellow on the outside and white on the inside. Furthermore, gold-plated jewelry feels lighter to the touch; it is harder than pure gold jewelry, does not leave marks when bitten, and is not easy to bend. Over time, the gold plating on such jewelry tends to peel off. 　Whether it’s gilded jewelry or plated jewelry. It’s still copper jewelry; it generally doesn’t have markings similar to those on gold jewelry. Or the stamp on it is different from that of gold jewelry; for example, some jewelry is engraved with the English letters “GK”, which means “plated gold”. Alternatively, if the stamp is blurred or uneven, consumers should determine the authenticity of gold jewelry by checking whether there is a stamp on it, whether the stamp meets the aforementioned requirements, and whether it is clear.