Graded diamonds-Diamonds are known as the "king of gems" in the world because of their highest hardness, crystal clear texture and dazzling features. It symbolizes success, elegance, loyalty, eternity and innocence, so it is deeply loved by people. At present, diamond is the most traded gem in the world jewelry trade. Since the advent of portable detection instruments such as thermal conductivity meter, it has become a very simple matter to identify the authenticity of diamonds, but how to evaluate the quality of a diamond has become the main problem in diamond trade. According to the latest national standard GB/T 16554- 1996 "Diamond Classification", there are four factors to evaluate the diamond grade, namely color, clarity, cut and carat weight. These four factors are also called "4C" criteria. "4C" is the first letter C in four English terms: color, clarity, cut and carat weight. 4C is an indispensable comprehensive factor to evaluate the quality of a diamond, and it is also a measure for consumers to judge the value of a diamond. There are all kinds of diamonds in the jewelry market, including pure natural diamonds and irradiated and filled diamonds. There are white diamonds (actually colorless with white characters on a white background), yellow diamonds, and red, green, blue and orange colored diamond. From the shape, there are standard round diamonds, as well as heart-shaped, oval and pear-shaped diamonds. The most common diamonds in the market are white (colorless) standard round diamonds, so in the "4C" standard, the classification of diamond color, clarity and carat weight only refers to the classification of natural white (colorless) to light yellow (brown, gray) series polished diamonds with carat weight greater than 0.2, while the cutting classification only refers to standard round diamonds or white (colorless) to light yellow (. The "4C" standard is not applicable to the classification of colored diamonds, irradiated diamonds and filled diamonds. In the "4C" standard, the color of diamonds is divided into 12 grades. The grading method is: the pure colorless diamond is defined as the highest color pole-extremely white, 100 color, which can be expressed by D or written as D( 100). With the increase of the yellow component of diamonds, the color grades gradually decreased to E(99), F(98), G(97) and H(96). In the diamond appraisal certificate, the color grade is usually expressed only by English letters. When the color grade is lower than n, it is generally considered that the diamond is no longer suitable for cooperative jewelry. The color grading of diamonds is determined by professional technicians who compare the diamonds to be graded with standard colorimetric stones repeatedly in the grading environment of specified standards. Or use a colorimeter to scan the diamonds to be classified in the visible range, and then determine them through a series of technical analysis and processing; The purity of a diamond is its purity. The higher the purity of a diamond, the less impurities, defects or flaws there are, and vice versa. Objectively speaking, flawless diamonds are rare. According to the standard, carefully observe the internal and surface defects of the diamond to be graded with a magnifying glass of 10 times. Under this condition, the clarity of diamonds can be divided into five grades: flawless LC, extremely defective VVS, slightly defective VS, defective SI and severely defective P, and further subdivided into sub-grades 10, namely LC, VVS 1, VVS2, SI 1, SI2 and P. Diamond cutting refers to the proportion and decoration degree of cut diamonds, which is an index directly influenced by human factors in 4C standard. The brilliance of diamond is attributed to its unique high refractive index and high dispersion (commonly known as "fire color"). Only excellent and proportional cutting can make all the incident light reflect, so as to show the unique luster, luster and flash of diamonds to the maximum extent. If the cutting is rough and disproportionate, it will cause "light leakage". Even if a diamond has good color and clarity, it can't have good light and its value. The simple way for consumers to judge the cutting quality is to pick up the diamond and stare at the shining light on the top of the diamond. If there are not many colors, the cutting is not ideal. According to the standard, cutting is divided into three grades: very good, good and average; The unit of mass (commonly known as weight) of diamonds is grams, but "carat" is still used as the unit of mass (weight) of diamonds in international diamond trade. 1 carat = 200mg = 0.2g. 1 carat is divided into 100 parts, and each part is called10.8. When the color pole, clarity and cutting conditions are similar, with the increase of diamond weight, its value increases geometrically. Consumers should choose diamonds of suitable size according to their hobbies and actual conditions. Diamond cutting and grinding technology: A rough diamond looks unremarkable, and it must be carefully cut and ground to become a sparkling diamond that we are used to. Therefore, the lathe work of diamonds directly affects the value of diamonds, which will be described in detail later. The most ideal cutting effect is of course to keep the maximum weight of the diamond, minimize defects, fully display the beauty of the diamond and make the diamond shine. The general cutting process includes the following steps: scribing (scribing): This is the first step of diamond cutting. First, check the blank and mark the surface of the diamond. The people who do this job are experienced and proficient in processing technology. The ultimate goal is to make the biggest, cleanest and most perfect diamond, so as to reflect the value of diamond as high as possible. The scribe must pay attention to two points: try to keep the maximum weight and minimize the content. The scriber studied the structure of the drill blank with a magnifying glass. If it is a big diamond, this work may take several months, but it will take several minutes for ordinary rough diamonds. However, no matter how small the rough diamond is, every diamond must be carefully examined before a correct judgment can be made. The scribe marked the blank with Indian ink, indicating that the blank should be divided along this line. Usually as far as possible along the natural grain direction of diamonds. Split the original stone: including chopping and sawing. Cleavage: Put the marked diamond blank on the frame with a cleaver, then use another diamond to make a dent along the parting line, then put a square knife on the dent, and beat it with proper force with your hand on the cleaver, so that the diamond will be split into two halves or more along the grain direction. Saw: most diamonds are not suitable for chopping, so they need to be cut with a saw. Because only diamonds can cut diamonds, the saw blade is a phosphor bronze disc with diamond powder and lubricant on the edge. The diamond is fixed on the fixture, and the saw disc rotates at high speed, so that the diamond can be sawed. Modern laser technology introduces diamond cutting, which greatly improves the machining efficiency of drill blanks. Molding: send the sawed or chopped diamonds to the grinding part for grinding and molding, that is, make the diamonds into common cut flowers or other special shapes such as round, heart-shaped, oval, pointed and emerald according to the design requirements. Because diamonds are the hardest natural substance recognized by human beings so far, only diamonds can polish diamonds, and the hardness of diamonds is slightly different in all directions. Therefore, when polishing, it is necessary to grasp the basic forms of diamonds by experience: cubic, octahedral, dodecahedral and crystal characteristics. The general method is to rotate the drill blank at high speed on the lathe, and then round the rotating drill blank with the diamond on the other arm. Tapping and polishing: On a cast iron disc coated with diamond powder and lubricating oil, all valve surfaces (facets) are turned and ground, making the diamond shine and attract attention. The grinding process is usually as follows: first, make 8 large faces at the bottom, and then make 16 small faces. With the sharp bottom, ***25 facets are corrected correctly, thus extending triangular facets, kite facets and waist facets, and ***33 facets, so that a round diamond has ***58 facets, and if there are no small facets with sharp bottom, there will be * * * 57 facets. Not every diamond blank has to go through all five processes, which depends on the characteristics of the diamond blank and the goal to be achieved. For example, for the aforementioned "flat" diamond rough, the splitting process may not be needed, and for the processing of emerald diamonds, the "rounding" process may not be needed. However, in any rough diamond, there are two essential processes, namely "scribing", "peeling" and "polishing". The position and angle of the petal surface produced by a finely crafted diamond are accurately calculated, so that the diamond shines with the greatest brilliance. It can be seen that cutting the world's hardest gem-diamond requires not only advanced equipment, but also rich experience, high sense of responsibility and the concentration of the cutter to release all the brilliance of the diamond. A diamond in the jewelry counter may be processed, inlaid and made by several people in many countries to become a diamond jewelry. With the development of science and technology, the introduction of laser technology and computer description can make the design and cutting of drill blanks more accurate.