(a) Cutting faceted stones.
There are many kinds of faceted gems, among which the most basic ones are round faceted, rose-shaped, stepped and mixed. According to these four basic cuts, hundreds of styles have evolved. Because these four basic cutting patterns are all derived from the cutting patterns of diamonds, they are exactly the same as the cutting patterns of diamonds, and their angles only change according to the different kinds of gems during processing. Therefore, for the cutting pattern of faceted gemstones, refer to the cutting pattern of diamonds in the first section of this chapter.
It should be pointed out that:
1) Although the rose-shaped cutter has beautiful geometry, it is not good for the fire color and brightness of gems, so it is rarely used now, and it is only occasionally seen in the cutting and grinding of small flat diamonds, zircon and garnet.
2) Emerald type in stepped cutting is mainly used for emerald cutting, and it is also suitable for all transparent gemstones, especially colorful colored gems. The number of facets and steps of this cutting is not the most important, because the beauty of color is in the primary position, while the fire color is in the secondary position. Therefore, besides step cutting, diamond processing also needs strict facet size, proportion, crown angle and pavilion angle. Generally, gemstones have larger countertops, thinner crowns and thicker pavilions.
3) Mixed cutting can make the fire color, color and weight of gems achieve the best effect, but because of the complex processing, it is not conducive to mass production, so it is limited to the design and pondering of high-grade gems. The common style is that the crown is round faceted and the pavilion is stepped.
4) colored gems's "Millennial Worker" (Figure 5- 1-32(a) and "Lattice Worker" (Figure 5- 1-32(b)) which are popular in the market in recent years are also evolved from four basic patterns. They have changed in processing equipment and proportion, and their styles are novel. Among them, every face of "Millennium Project" is concave, which has the function of concentrating light and enhancing the brightness of the gem surface; "Gezi Palace" can be divided into single-sided and double-sided, each side is square or diamond-shaped, concise and lively, full of modern flavor.
Figure 5- 1-32 Millennium Jewelry (a) and Checked Jewelry (b)
(2) Design of faceted gemstones
Faceted type is suitable for all colorless and colored transparent gemstones. The design of faceted gemstones, like the design of globoidal gemstones, needs to complete the steps of naming the original stone, understanding the internal and external characteristics of the gemstone, analyzing the original stone and selecting the design scheme. The design of specific faceted gems can be mainly carried out from four aspects: color, weight, defects and proportion.
1. color design
The color of a gem is related to its thickness and particle size, so in the design, the light-colored rough stone can be designed as rough cut, for example, aquamarine is often designed as emerald to enhance the chromaticity. Similarly, the darker rough stones are designed to be cut with smaller thickness, such as Shandong sapphire. If it is designed as a stepped square (emerald crown and flat bottom), the thickness will be thinner and the chromaticity will be weakened.
In addition, the use of improved styles can also improve the color of gems. For light-colored gems with low refractive index, such as light-colored topaz and crystal, the improved round diamond style with vertical main facets is adopted, and more facets in the pavilion are used to reflect light at the same time to enhance its luster effect. For amethyst and tea crystal with lighter color, in addition to the step type, you can also choose the improved round drill type or miscellaneous stone type with horizontal main surface to increase the height of the gem, so as to achieve the effect of deepening the color (see Figure 5- 1-33). For dark gemstones, such as deep red garnet and Shandong sapphire. The improved round diamond type (that is, the height of the pavilion is appropriately reduced) is selected to make it leak light to reduce the color concentration of the gem, thus improving the color of the gem.
Figure 5- 1-33 Cutting Process in Color Design
2. Weight design
When cutting and grinding precious stones from raw materials, the material loss is great, such as diamonds, and the weight loss is often above 50%. According to some data, the yield of Shandong sapphire is only about 30%. The loss of weight is directly related to the value of goods. Therefore, in the case of reflecting the overall aesthetic feeling of gems, care has become an important topic for gem craftsmen.
Weight includes two meanings, that is, the finished product of a single gem should be as large as possible, and the total output of a raw material after processing should be high. Which is the main one depends on the specific situation.
For low-grade gemstones, output is generally the main factor. Because at this time, the price of gemstones is directly proportional to the weight, and the higher the output, the higher the price. For high-grade gems, the price of a single gem is higher. Because the price of this kind of gem is not directly proportional to its weight, sometimes it is exponential, and the price of a large and precious gem variety is immeasurable.
There are four ways to increase the weight of a single gem:
(1) Increase waist diameter
(2) increase the waist thickness
(3) Increase the depth of the exhibition hall
(4) Improve the original gem style.
The first three methods are shown in Figure 5- 1-34. The fourth method is often to change the table top plane of the gemstone into a curved surface, so as to receive more light and make the gemstone look brighter, such as "Millennium Work" and "Lattice Work", but this kind of grinder has greater loss and higher cost.
Figure 5- 1-34 Three methods to increase the weight of gemstones
3. Design of defects and inclusions
Defects and inclusions are the main factors affecting the clarity of gemstones. In the process of gem processing, six factors should be considered for inclusions and internal defects: size, quantity, position, color, outline and transparency.
In the design of defects and inclusions, we should take the following measures:
1) colored inclusions and large cracks should be removed when cutting the original stone along the crack surface.
2) When designing the original stone, try to understand the position of defects and inclusions and mark them.
3) Based on the principle of removing large flaws or inclusions first, then removing small ones, it is best to reduce the size of the pattern and remove hidden cracks.
4) For indelible flaws or inclusions, try to design them in a place that will not affect the beauty of the gem, that is, an inconspicuous place near the waist (see Figure 5- 1-35). It should be noted here that: ① inclusions under the gem table are easy to be found; ② The contents in the museum are easily reflected into multiple images, forming a "starry sky"; (3) Emerald inclusions are easy to be found anywhere, including the waist, so clean raw materials should be used when designing this cutting.
Fig. 5- 1-35 Location of processing inclusions
5) The inclusions with bright colors, regular shapes, clear outlines and easy observation can be fully utilized, such as insects, water bile agate and hair crystals in amber.
4. Proportional design
In the design of faceted cutting, the table size, crown angle, waist thickness, pavilion depth and other factors should be fully considered, so that the body color, brightness, fire color and shining degree of the gemstone after cutting and polishing can achieve the best effect.
Design of (1) table size
The size of the table is relative to the waist diameter of the gem. For colored gems, the size of the table affects the color, fire color, shining degree and weight of gems. What needs to be emphasized here is that color includes hue, lightness and saturation. Among them, the lightness of color is also called lightness and brilliance, and its "fire color" related to dispersion is a pair of contradictions in design, because lightness is the total amount of reflected light and transmitted light of various colors, and strong lightness means that the total reflection of each monochromatic light in a gem is relatively strong, and any reduction of reflected light of monochromatic light will weaken lightness. The requirement of fire color is just the opposite, which requires that the reflection of each monochromatic light is inconsistent, some monochromatic light should be reflected more and some should be smaller, so as to show excellent dispersion, that is, fire color. It is for this reason that brightness and fire color cannot reach the best state at the same time. Therefore, in the proportion design of gemstones, what we pursue is their comprehensive effect, which is a compromise between the two. This trade-off is often referred to as sparkle. Understanding the above relationship is very helpful for our scale design.
For gems with strong dispersion effect, such as diamonds, zircon, etc., the table should be lowered correspondingly when designing, because the dispersion area is mainly concentrated in the inclined surface area of the crown. Reducing the mesa will increase the slope area of the crown, and the light will reflect from the pavilion at different refraction angles. However, if the dispersion increases infinitely, the brightness of the gem will be greatly reduced, which is also unfavorable to the weight of the gem. If the color of the gem is darker, the increase of the table top can be improved, because more light can be transmitted. However, when the table top exceeds 2/3 of the waist diameter, the light reflected by the table top will suppress the light in the inclined plane area, resulting in a "halo" reflection effect, which makes the gem look dull.
(2) Design of crown angle
Crown angle refers to the acute angle between the main facet of the crown and the waist plane. When the waist diameter is fixed, its size is determined by the desktop and crown height.
Under the condition of constant waist diameter and crown height, the change effect of crown angle is the same, crown angle increases, table top increases, crown angle decreases and table top decreases.
According to the calculation of gem refractive index or the relationship curve between gem refractive index and critical angle, the angle of faceted gem crown can be obtained. The specific calculation formula is as follows:
β=8×(45 amps)
Where: β-crown angle, unit: degree; α—Pavilion angle, in degrees.
After determining the crown angle, the angle between the star facet and the upper waist surface is obtained according to the following relationship:
Star facet angle = crown angle -( 12 ~ 7)
Upper waist angle = crown angle+(5 ~ 9)
(3) Design of waistline thickness
The waist is the inlaid edge of the gem, and its thickness directly affects the weight and perfection of the gem. Too thin will easily lead to waist injury, too thick will produce fuzzy gray reflection. As far as the standard round drill style is concerned, the waist edge is composed of 16 curves with alternating thickness, and the waist thickness changes as follows:
{δ} mm = {a }+{ b} mm2/{d} mm.
Where: δ-waist thickness; D- waist diameter; A-empirical coefficient, which is 0.017mm; B— empirical coefficient, 0.05 ~ 0.08mm2.
(4) The design of pavilion angle
Pavilion angle refers to the acute angle between the main facet of the pavilion and the waist plane, and its size is determined by the waist diameter and the pavilion depth.
The angle of the pavilion has a great influence on the brilliance of the gem, because the correct angle of the pavilion can reflect as much light as possible from the pavilion facet to produce the maximum brightness (as shown in Figure 5- 1-36(a)).
If the angle of the pavilion of the gem is less than the normal range, the depth of the pavilion will be reduced, and the light entering the gem will leak from the pavilion. Looking down from the table, there will be a "window" in the center, which is the fisheye effect (as shown in Figure 5- 1-36(b)).
If the pavilion angle of the gem is larger than the normal range, the depth of the pavilion will increase, and the light entering the gem will also leak out from the pavilion. From the table, the center darkens, resulting in a "nail head" effect or a black background effect (as shown in Figure 5- 1-36(c)).
Figure 5- 1-36 gemstone optical path diagram
Ideal processing; (b) small thickness (fisheye effect); (c) large thickness (black matrix effect)
The formula for calculating the angle of two-dimensional stone pavilion described by American gemologist E.S.Love is as follows:
if
if
Where: A is the protagonist of the pavilion, φ is the critical angle of the medium, and all units are degrees.
For diamonds, the pavilion angle is about 40, but for other gems, this angle varies according to the refractive index. Generally speaking, the lower the refractive index, the greater the pavilion angle of the gem, that is, the deeper the pavilion, so as to generate internal reflection and increase the sparkle.
See table 5- 1-4 for the critical angle, crown angle and pavilion angle of common gems.
Table 5- 1-4 Crown Angle and Pavilion Angle of Common Gems
sequential
(3) Orientation and direction of facet cutting
Faceted gems do not have the cat's eye effect and starlight effect of globoidal gems, but in order to better reflect the body color, brightness, fire color and shining degree of transparent gems, it is also necessary to locate them. The positioning of faceted gems is mainly the positioning of the table, and the method is as follows.
1. Gemstones with obvious multicolor colors.
Heterogeneous gemstones are polychromatic, mostly inconspicuous, which can be ignored in design and positioning. Ruby, sapphire, tourmaline and tanzanite are common gems with obvious polychromatic properties, so there are orientation problems in design. The orientation and positioning of different gems are different, depending on the specific situation. Sapphire, for example, is generally blue when viewed from the direction parallel to the crystal axis (Z axis), but it tends to show a certain yellow-green color when viewed from the direction perpendicular to the Z axis. When designing, the cutting table is usually selected in the direction perpendicular to the Z axis of the crystal, so that a softer blue color can be obtained. Another example is green tourmaline, which is usually bright green or turquoise when viewed from the direction perpendicular to the Z axis, and often dark brown green or dark olive green when viewed from the direction parallel to the Z axis. When designing, the cutting table is usually selected in the direction parallel to the crystal Z axis (see Figure 5- 1-37). However, if the color of tourmaline is extremely light, sometimes it is necessary to choose the direction perpendicular to the Z axis as the countertop, which can increase the depth of the color.
Figure 5- 1-37 Positioning of sapphire table (a) and positioning of green tourmaline table (b)
2. Gemstones with no or no obvious multicolor.
Because the color of this gem has not changed or changed very little in all directions, the maximum use of the gem should be fully considered in the design. One way to ensure the size of the finished product is that the table top is parallel to the diagonal plane (see Figure 5- 1-38). Gems commonly used to determine the table position in this way are garnet, spinel, crystal and so on.
Fig. 5- 1-38 Table Positioning of Non-polychromatic or Obvious Polychromatic Gemstones
3. Gems with ribbons, color zones, color clusters and color spots.
Some gems have uneven color distribution in ordinary crystals, such as ribbons in sapphires, spots in amethyst and ribbons in tourmalines. If the direction of the countertop is not properly determined, the color distribution of the finished product may be uneven when viewed from the countertop, thus affecting its commodity value.
For sapphire ribbon, it is usually placed near the waist of the gem and parallel to the table, so that the color of the ribbon can appear uniform, positive and thick blue on the top through repeated reflection and refraction of light in the gem.
For amethyst clusters and spots, they are generally placed in the central area directly below the gem table, that is, the crown, waist or pavilion, so that the color is more uniform from above. If the stain is small, it is best to put it at the sharp corner of the pavilion, and through the reflection and refraction of light, the original colorless refracted light will be turned into colored light to achieve the effect of color enhancement (see Figure 5- 1-39).
Fig. 5- 1-39 color group and stain treatment
The color zone of tourmaline should be treated as appropriate. If the color area is irregular, you should use the above two methods to place the color area. If the colored areas are arranged neatly and brightly colored, the desktop can be positioned by the method shown in Figure 5- 1-40.
4. Cleave gems
For gemstones with cleavage development, it is very convenient to cut raw materials, but the polishing process of gemstone processing is difficult, and it is easy to generate heat to break the table top. Therefore, in the positioning of the original stone, it should be avoided that the mesa is parallel to the cleavage plane, and the mesa and cleavage plane can be oriented at an angle of 5 ~ 10 (or 80 ~ 85) or parallel to the longitudinal axis. If the cleavage number of the original stone is large, its trend should, in principle, avoid the mesa being parallel to the group with the most developed cleavage (see Figure 5- 1-4 1).
Fig. 5- 1-40 multi-color tourmaline desktop positioning
Fig. 5- 1-4 1 cleavage gemstone for table positioning
(4) Selection of faceted gems
Traditionally, transparency is regarded as an important measure of whether faceted cutting is adopted. Faceted cuts are often used for transparent gemstones, and arc cuts or other cuts are often used for opaque gemstones. The choice of faceted gemstone raw materials is much stricter than that of globoidal gemstones, because the price of faceted gemstone raw materials is higher, and if it is not chosen properly, the loss will be great. It is difficult to infer the quality of a gem from its appearance. The value of a gem often lies not only in its beautiful appearance, but also in its good internal texture.
First of all, we should check the color properties and distribution of raw materials. Many gems have obvious multi-colors, ribbons or ribbons, and if they are properly positioned, their value can be doubled.
Secondly, check the shape of raw materials. Many raw materials are flaky or serrated, which is not conducive to the utilization of raw materials and has a great impact on the yield. Gemmologists can accept gem crystals with regular shapes. Tourmaline, for example, is usually a slender pencil with a triangular fracture. This is very close to the emerald cutting style, so the loss is very small when cutting and grinding. Garnet crystals tend to be round and spherical, which is beneficial to processing into round diamond-shaped patterns.
Check the quantity and distribution of defects and cracks in raw materials again. When selecting materials, check from all angles and imagine the shape and size of raw materials after cutting along cracks. If the estimated loss may exceed 60%, be careful when choosing materials. In addition, we should understand the nature of cracks. Natural cracks are often caused by iron pollution of dark brown or black filaments, while many small cracks left by hammer damage are white because of air, so we should be more careful when choosing such materials. Because there may be many cracks hidden in it. Therefore, in the gem processing industry, we are afraid of small cracks and big cracks.
Finally, check the weight of raw materials. The raw materials of gems should not be too small, which is not conducive to processing and inlaying, and the weight requirements for different gems are also different. Generally speaking, it is required to be above 0.6ct, and the group gem can be reduced to above 0. 1ct. For gem crystals, the particle size is required to be above 5mm, and the precious one can be above 3 mm.
There are many kinds of faceted gemstone materials, such as diamond, ruby, sapphire, emerald, aquamarine, metamorphic rock, tourmaline, feldspar, crystal, topaz, olivine, spinel, garnet and so on.
(5) Processing technology of faceted gemstones
The processing technology of faceted gemstones is much more complicated than that of globoidal gemstones, which is divided into nine processes: discharging, winding, crown grinding, crown grinding, winding, pavilion grinding, pavilion grinding and post-treatment.
1. Exempted
Cutting refers to cutting raw materials into small pieces, and then cutting a gem-style prototype with a repair saw. The saw blade for cutting is a thin iron plate with a diameter of 100 ~ 150 mm and a thickness of 0.3 ~ 0.5 mm, and its outer edge is engraved with more than 300 small grooves, in which 100 ~ 120 mesh diamond powder is embedded. The specific operation steps are as follows:
1) Clean the stone platform, and turn on the cutting machine and cooling water.
2) Cut off the skin of the raw material (if there is no skin, you can directly proceed to the next step). Hold the raw material in your hand and push it into the saw blade evenly. At first, feed slowly. In the middle of feeding, when the material is smooth, the speed should be increased. When the material is cut almost, the speed should be slowed down to avoid cracking.
3) Cutting raw materials along deep cracks. In this way, blanks with different sizes can be obtained.
4) Observe the blank carefully, mark the cotton crack position that is not easy to observe with ink lines, and avoid designing it as a jewel-like outline.
5) If the sensible particle size is still large, it needs to be further divided. It is required that the blank cut out should have more large particles, less small particles and less scrap at the corners, and the blank size can be accepted by the gem style.
6) Gem blanks are divided into regular and irregular shapes. Regular blank (cube, square prism) can be divided into two parts along the opposite side by cutting machine, or into one big part and one small part by parallel diagonal plane. The resulting cross section is square or rectangular. Square is suitable for cutting into circles, hexagons, octagons and squares. Rectangles are suitable for processing into oval, stepped and olive shapes.
Irregular blanks should be cut into an inverted cone, and the height of the cone should be more than half of the long side of the top surface, which is conducive to style design. If the top surface of the cone is approximately regular polygon, the blank can be designed into circular, square and other cutting shapes; If the cone is close to the hull, the blank can be designed into oval, stepped and other shapes; If one end of the top surface of the cone is large and the other end is small, the blank can be designed as a water drop or a heart. If the length of the top surface of the cone is much larger than the width, the blank can be designed into an olive isometric shape.
The above is the blanking process of middle and low grade gems. For high-grade gemstones, it is not advisable to cut them into small pieces unless there are serious defects such as cotton and cracks in the raw materials of the gemstones. For high-grade gems, waste should be simply removed to reach the initial blank.
Climb the pole
Sticking refers to gluing the blank and stick together with glue. The winding of faceted gemstones is much more complicated than that of convex gemstones, because faceted gemstones need more accurate angles during grinding.
The adhesive stick is mainly made of brass or iron, and its length is generally100 ~150 mm. The adhesive end of the adhesive stick has various shapes to bond different cut gems (see Figure 5- 1-42). Glue is usually black wax glue or red wax glue.
Figure 5- 1-42 Sticking rod
The specific operation steps of the upper rod are as follows:
1) Clean the surface of the rod and gem blank.
2) Crush the glue, put it in a fire cup and heat it with an alcohol lamp until it melts.
3) Heat the bonded end of the rod, and then evenly heat the blank. If the blank is afraid of heat, heat it separately with asbestos mesh.
4) Stick the stick and the blank together, and correct the angle when the glue is not completely solidified. It is required that the center line of the blank coincides with the axis of the rod, and the top surface coincides with the rod until it is naturally cooled.
The above rod loading process is for experienced jewelers. For beginners, in order to make the angle of the blank accurate, a rod-type bonding frame should be used. Its structure and method are not detailed here.
3. Ring shape (the following procedures are based on Topaz's standard round drill type)
Ring refers to the basic cambered surface of the waist and crown of the gem, and the abrasive used for ring is 180 # ~ 220 #. When winding the waist shape, ensure that the axis of the bar is parallel to the grinding surface, so that the top surface of the blank can be perpendicular to the waist surface. When circling the basic cambered surface of the crown, the radian should be small, that is, the included angle between the cambered surface and the bar should be small. The curvature of the cambered surface should be consistent, otherwise it will affect the facet grinding of the crown. See Figure 5- 1-43 for the grinding method.
Figure 5- 1-43 Ring shape of jewel crown
4. Crown grinding
Crown grinding refers to the use of gem carving grinding machine to drive the blank to grind small faces with different angles on the grinding disc. Gemstone carving mill generally adopts octagonal hand carving mill and manipulator carving mill. The grinding disc is generally a diamond grinding disc with a diameter of 150mm and a particle size of 600 mesh. The specific operation steps are as follows:
1) Turn on the grinder and cooling water.
2) Install the billet bar on 45 blocks, and then put it into 45 blocks. Install the stopper on the gemstone carving and grinding machine, so that the table top faces down and is parallel to the grinding table, and then grind the gemstone table top flat (see Figure 5- 1-44).
Fig. 5- 1-44 Grinding 45 crown blocks.
3) Take off the 45 stop, directly install the billet bar on the gemstone carving machine (take the octagonal hand carving grinder as an example), adjust the main platform to make the gemstone contact with the grinding disc at 40, and adjust the octagonal hand to the L hole position. By rotating the octagonal hand on the eight sides of the platform, the eight main surfaces of the crown can be ground. At this time, the size of the main surface should be consistent, and the diameter of the table should reach 50% ~ 60% of the waist diameter.
4) Lift the main platform so that the blank forms an angle of 23 with the grinding disc, and adjust the "octagonal hand" to the position of 2 holes. The eight star facets of the crown can be ground by octahedral rotation. At this point, the facet and the main surface of the star just form two squares.
5) Lower the main platform so that the blank forms an angle of 46 with the grinding disc, adjust the "octagonal hand" to the position of 3 holes, and grind the eight waist surfaces on the left side of the crown through the rotation of eight sides.
6) Keep the platform still, adjust the "octagonal hand" to the position of 4 holes, and through the rotation of eight sides, the eight waist surfaces on the right side of the crown can be polished. At this time, the crown was polished. It should be noted here that during the grinding process, the contact between the gemstone and the grinding disc should be light and the strength should be appropriate, and the grinding progress should be continuously observed.
Polishing crown
The polishing disc used for polishing is generally a copper disc and the polishing agent is diamond powder. The specific operation steps are as follows:
1) Remove the grinding disc, put on the polishing disc, start the machine and apply a small amount of polishing agent.
2) Find a suitable angle by sticking oil, which must be absolutely consistent with the grinding angle, otherwise there will be redundant facets. The polishing sequence is to polish the star surface first, then the main surface and finally the waist surface.
3) Change it to 45. Block, and polishing that gemstone table by the oil stick method.
Climb the pole
After the crown is polished, put the gem blank on an alcohol lamp to heat it, then take it off, turn it over, and stick the crown on a flat-headed stick. See the second procedure for the method.
7. Polishing the pavilion
The specific operation steps are as follows:
1) Install the stick on the octagonal handle.
2) Adjust the host platform to make the blank form an angle of 40 with the grinding disc, select the position of 1 hole of the octagonal hand, and polish the eight main faces of the pavilion through eight-sided rotation.
3) Lower the main platform so that the blank forms an angle of 43 with the grinding disc, select the position of 3 holes of the octagonal hand, and through the rotation of eight sides, eight waist facets on the left side of the pavilion can be ground. The length of the waist facet should be 2/3 of the length of the main facet of the pavilion.
4) Keep the platform still and select the four holes of the octagonal hand. Similarly, the eight waist surfaces on the right side of the pavilion can also be ground.
Step 8 polish the pavilion
The method of pavilion polishing is the same as crown polishing. The order is to cast the main face of Hall 8 first, and then cast the 16 waist face.
9. Post-processing
The specific operation steps are as follows:
1) If you are afraid of damage to the cabinet bottom tip, you can grind a small plane at the cabinet bottom tip, and the grinding and polishing method is the same as before.
2) Polishing the waist For the overall beauty of the gem, the waist can be polished.
3) Glue removal treatment: heat the gem, stick it with alcohol lamp to melt the glue, and unscrew the gem.
4) Cleaning treatment: put the gem and stick with glue into alcohol respectively, take out the gem and stick after the glue dissolves, and clean them with clear water.
At this point, the faceted gem has been processed.