What is the difference between gold leaf, gilt, gold-filled, gold-plated, and gold painting?

　　People often talk about various terms related to gold, such as 'liujin' (鎏金), 'baojing' (包金), 'tiekin' (贴金), 'dujin' (镀金), 'miaojin' (描金), and even 'tangjin' (烫金) and 'yajin' (亚金). These terms relate to gold-making techniques or products; some use real gold, while others use other yellow metals. It's easy to confuse them, so here's a brief explanation:

　　(1) Liujin (鎏金)

　　This is an ancient traditional craft. Archaeological evidence shows that this technique began in the mid-Warring States period. The liujin process mainly involves combining gold and mercury to create a gold-mercury paint, which is then applied to the object according to the pattern or requirements. After baking, the mercury evaporates, leaving the gold firmly attached to the surface. The gold-mercury paint can be applied multiple times to enhance the effect. The gold is very firmly attached and not easily removed.

　　(2) Dujin (镀金)

　　The true electroplating gold process has not been around for very long, only about a hundred years. However, the technology is very mature. Currently, most artworks, jewelry, fine decorations, and precision parts use gold plating. The gold plating layer is corrosion-resistant, wear-resistant, and high-temperature resistant, with a beautiful golden luster. Gold plating methods include cyanide gold plating, low-cyanide gold plating, and cyanide-free gold plating. Gold plating is divided into two categories: homogeneous material gold plating and heterogeneous material gold plating. Homogeneous material gold plating refers to gold plating the surface of gold jewelry to improve its brightness and color. Heterogeneous material gold plating refers to gold plating the surface of non-gold materials, such as silver plating gold or copper plating gold, to enhance the appearance by using the luster of gold.

　　The quality of gold plating depends on the thickness and brightness of the plating layer. The internationally accepted standard for gold-plated jewelry is: good gold-plated jewelry has a plating thickness of 10-25 micrometers, while general gold-plated jewelry has a plating thickness of 2-3 micrometers. Jewelry with a plating layer below 0.18 micrometers is not called "gold-plated" but "gold-coated," and it belongs to inexpensive jewelry crafts.

　　According to its process characteristics, gold plating is divided into cyanide-free gold plating and cyanide gold plating. Currently, the quality of cyanide (potassium cyanide) gold plating is better, with better color, adhesion, and wear resistance than cyanide-free gold plating. In recent years, with the advancement of electroplating technology, there have been new breakthroughs in gold plating. In the past, gold-plated jewelry only had one gold color. Now, French, American, and Japanese gold-plated jewelry has three or more colors. The colored gold electroplating, known as tricolor gold, includes rose, silver-white, gold, black, blue, and other colors. Generally speaking, the plating layer of homogeneous gold plating does not need to be too thick; 2 micrometers is sufficient. The plating layer of heterogeneous gold plating should be thicker. Some countries stipulate that the gold plating layer of such products must reach more than 10 micrometers, while some international companies have even higher requirements, requiring 12.5 micrometers to be considered qualified.

　　(3) Tiejin (贴金)

　　Tiejin (贴金) uses gold leaf as a raw material. Gold leaf can be applied to create a smooth surface or be processed into exquisite patterns. Many imperial palaces and temples use gold leaf on their carved beams and statues, making the buildings magnificent. Tiejin is a traditional and special craft. Before the advent of modern baojin (包金) technology, tiejin and baojin had the same meaning: applying a very thin gold leaf to the surface of an object for protection. With the development of modern baojin technology, tiejin has become a unique craft. Traditional tiejin involves first making high-karat gold into extremely thin gold leaf, which has strong adhesion and good mutual attraction to some smooth materials. In the past, in addition to some crafts, a large amount of gold leaf was used for Buddha statues, signs, and buildings. Tiejin has high application value for products that cannot be processed using gold plating and baojin techniques. Abroad, many large decorative items and the surfaces of some non-metallic items are processed using tiejin technology.

　　(4) Baojin (包金)

　　Thin baojin uses gold leaf, mainly for luxurious ornaments and building decorations, similar to tiejin. Thick baojin uses gold sheets, often used in the production of large metal crafts and the exteriors of some jewelry. Currently, there are many imported baojin jewelry on the market. These jewelry pieces look exactly like gold jewelry, with a brilliant and colorful luster, making them very attractive, but at a lower price. This effect is due to its "glamorous coating," the baojin layer. The inner material of baojin jewelry is not gold or silver but alloys of aluminum, copper, zinc, etc., with a layer of gold wrapped around the surface, like wrapping paper, to play a decorative role and compete with gold jewelry. The quality of baojin jewelry depends on the success of the baojin process. This process has high requirements. For example, US-made baojin jewelry must indicate its characteristics and the proportion of K gold, such as (1/10.14K.GF), meaning jewelry with a 14K gold coating, where the baojin amount must account for one-tenth of the total weight of the jewelry; otherwise, it is not qualified. If the baojin material uses less than 10K gold, or the baojin weight is less than one-twentieth of the total weight of the jewelry, the term "baojin" cannot be used. Baojin jewelry has high wear resistance. We can see some baojin jewelry that has been used for decades, and the surface color remains unchanged, without revealing the inner core. Its service life is longer than that of gold-plated jewelry.

　　(5) Zujin (注金), Baojin (包金)

　　The baojin process was patented by J. Boss on May 3, 1859. Baojin cases were more common than solid gold cases. Early pocket watches only had five percent solid gold or pure gold cases, which were expensive and only worn by high-ranking officials and the wealthy to show their status.

　　The method at that time was to sandwich two 12-inch long gold bars (2 inches wide, half an inch thick) between a 3/4-inch metal bar, with the length and width the same as the two gold bars. The three metals were welded together under high temperature and pressure like a sandwich, then pressed into a metal sheet by a high-pressure roller, and then stamped into a round watch case or cover by a stamping machine.

　　Early baojin cases were mostly 10K and 14K. The watch cases were stamped with a "Guarantee" of 10, 15, 20, 25, and 30 years of wear resistance. The higher the number of years, the more gold and the greater the thickness.

　　In 1924, the government prohibited manufacturers from using the word "guaranteed". After that, watch case manufacturers could only mark watch cases with 10K gold or 14K gold-filled. Therefore, if the word "guaranteed" appears, the gold case is gold-filled, and the watch case must have been manufactured before 1924.

　　(6) Gold Tracing

　　This is a traditional process where gold is dissolved in mercury and salt solutions, then the mercury and salt solutions are heated and evaporated to obtain gold powder. This gold powder can then be used for decorative painting, even for drawing pictures, copying scriptures, etc.

　　(7) Karat Gold

　　The "K" in K-gold is an abbreviation of the foreign word "Karat". The full expression is: Karatgold (i.e., K-gold). The method of measuring K-gold is: pure gold is 24K (100% pure gold content), and 1K has a gold content of about 4.166%. The method of calculating gold content using "K" originated from a carob tree on the Mediterranean coast. The carob tree bears pale red flowers and pods about 15 centimeters long, with brown beans that can be used to make glue. No matter where this tree grows, the size of its beans is exactly the same, so in ancient times, people used it as a standard for measuring weight. Over time, it became a unit of measurement used to measure precious and minute items. At that time, diamonds and gold were also measured using this unit, which was "Karat". It was not until 1914 that "Karat" was internationally standardized to its current form. This year, K-gold has become the focus of the jewelry market. Strolling through jewelry counters in stores, consumers might ask when faced with colorful K-gold ornaments: Are these all K-gold jewelry? How is K-gold synthesized?

　　K-gold is made by processing pure gold with other materials. Since jewelry made from pure gold is too soft and difficult to set with various exquisite gems, especially when setting precious items like pearls, gemstones, and jade, which are easily lost, people have known since ancient times that adding appropriate amounts of metals like silver, copper, and zinc to pure gold can increase its strength and toughness. Gold ornaments made this way are called K-gold jewelry.

　　K-gold can be formulated into various colors as needed, such as red when gold is mixed with copper, which is called red K-gold. There are many colors of K-gold jewelry popular internationally, including orange-red, champagne, apple green, yellow, red, blue-green, milky white, black, and more than ten other varieties, collectively known as colored K-gold jewelry.

　　In addition, there is K white gold. When more than 25% palladium or nickel is mixed into gold, it becomes white gold. Its main component is still gold, and it is called K white gold.

　　Now that you understand the meaning and calculation method of K-gold, it's not difficult to know how many types of K-gold there are. According to international standards, K-gold is divided into 24 types, ranging from 1K to 24K. However, the types of K-gold used for jewelry do not reach 24 types. Currently, jewelry materials used in various countries are not less than 8K. Thus, the actual number of K-gold types truly considered for jewelry is 17.

　　Among these 17 types of K materials, 18K and 14K are the most commonly used, serving as primary jewelry raw materials in the jewelry industry of various countries. To enrich the expressiveness of various K-golds, foreign countries adjust other alloy ratio coefficients to synthesize K-golds of various colors while keeping the content standard unchanged. According to some jewelry magazines, there are currently 450 gold ratios, with 20 most commonly used. For example, 14K has 6 types: red, reddish-yellow, deep yellow, light yellow, dark yellow, and greenish-yellow; 18K also has 5 types: red, reddish, yellow, light yellow, and dark yellow.

　　The above craftsmanship and techniques all utilize gold. However, the following types of processes, despite having "gold" in their names, do not use gold as their material.

　　(8) Hot Stamping (Foil Stamping)

　　For aesthetic purposes, the text printed on some hardcover books or certificates is dazzling gold, which is what people call hot stamping. In fact, the material used for hot stamping is aluminum oxide or copper powder, which is firmly stamped onto the book cover with a type die under high temperature. This primarily serves a decorative purpose.

　　(9) Imitation Gold

　　Currently, some yellow craft jewelry appears on the market at relatively low prices, which sales staff refer to as imitation gold jewelry. In fact, imitation gold is not real gold and does not contain gold at all. However, imitation gold has the luster and color of 18K gold, and some possess the corrosion resistance and color stability of 18K gold. China has conducted certain research and application of imitation gold materials. The developed imitation gold is very similar to gold in color and slightly inferior to gold in corrosion resistance. For example, its discoloration property: after 100 hours of corrosion in a constant temperature test chamber, it can still maintain a high gloss with basically no discoloration; in an indoor atmospheric environment, there is basically no discoloration after two years of corrosion. Jewelry made from imitation gold materials does not require gold plating, which not only saves a large amount of gold for the country but also avoids environmental pollution caused by cyanide gold plating.

　　(10) Jin Gold

　　This metal contains more than ten metallic elements. Its processing performance and color are very similar to gold, and its properties such as oxidation resistance, wear resistance, and corrosion resistance even surpass gold. However, its specific gravity is only 40% of gold's, and its price is 1/10 of gold's. Jin Gold is very suitable for making imitation gold jewelry. Jin Gold is widely used in industry, partially replacing gold materials.

　　(11) Rare-earth Metal Gold

　　Rare-earth metal gold jewelry is jewelry made from rare-earth metal gold materials. Rare-earth metal gold material is a novel imitation gold material that uses copper as its main raw material, with added rare earths and other components. It features good wear resistance, hard texture, and a color closely resembling gold that is not prone to fading. Given its characteristics superior to general imitation gold materials, it has become a material for manufacturing higher-grade imitation gold jewelry.

　　Gold jewelry is relatively expensive. While gold-plated imitation jewelry is cheaper, the plating is prone to discoloration and loss of decorative appeal. Jewelry made from rare metals can exhibit the color of 18K or 20K gold and is resistant to oxidation and fading, making it suitable for everyday wear. Recently, some domestic manufacturers have developed a new type of rare metal jewelry called rare metal magnetic medicinal health jewelry. In addition to the characteristics of general rare metal jewelry, this jewelry also has special therapeutic effects and certain efficacy for some common and chronic diseases. According to domestic medical research institutions, its health benefits are significant. The successful development of rare metal magnetic medicinal health jewelry marks a breakthrough in the use of jewelry and will open up a new path for its multi-purpose applications. However, it must be noted that although rare metal jewelry can exhibit the golden color of 18K or 20K gold, it is not K gold. Do not mistake it for K gold to avoid economic losses.

　　Some jewelry on the market has markings, including the manufacturer's mark and the jewelry's fineness symbol, such as 24K, 18K, Pt900, etc. Some jewelry fineness markings are 18KP or 18KF. The former indicates 18K gold plating, while the latter indicates imitation 18K gold, such as imitation gold.

　　Note: Excerpted from "WeChat Public Platform: Xi'an Brothers Alliance VS World Ancient Beads and Ornaments"