Synthetic diamonds: synthetic diamonds and optimized diamonds. ?
Identification method of synthetic diamonds and natural diamonds;
1, identification method of synthetic diamonds
(1) synthetic diamond
[1] high temperature and high pressure diamond synthesis
Color: mainly yellow, orange and brown, and the price is very competitive; However, colors such as blue and nearly colorless are extremely difficult to see because of technical difficulty and high cost.
Internal microscopic characteristics: fine iron or nickel-iron alloy catalyst metal inclusions can be seen. Some synthetic diamonds are magnetic, and irregular ribbons and hourglass bands can be seen.
Cleanliness: mainly P and SI, some of which can reach VS or even VVS.
Absorption spectrum: there is no absorption line of 4 15nm.
Abnormal birefringence: very weak, and interference discoloration is not obvious.
Ultraviolet fluorescence characteristics: fluorescence is inert under long-wave ultraviolet light, and it has obvious banding phenomenon under short-wave ultraviolet light, which is light yellow, orange yellow and green yellow uneven fluorescence with local phosphorescence.
[2] CVD synthetic diamond
Color: mostly dark brown and light brown, and it is difficult to grow almost colorless and blue products.
Internal microscopic features: irregular dark inclusions and punctate inclusions can be seen. There can be equal growth zones.
Abnormal birefringence: there is strong abnormal extinction, and the extinction in different directions is also different.
Ultraviolet fluorescence characteristics: weak orange fluorescence under long and short wavelength ultraviolet light.
(2) Optimizing the treatment of diamonds
[1] color optimization processing
(1) traditional color optimization:
The ancient treatment method is to coat a thin layer of blue substance with high refractive index on the surface of diamond, which can improve the color of diamond by 1-2 grade. What's more, the surface of the diamond is coated with ink, oil paint and nail polish. In order to improve the color level of the diamond, some people added metal foil to the base of the diamond ring. These methods are primitive and easy to identify.
② Irradiated colored diamonds and their identification:
Irradiation discoloration is a physical discoloration method, which is only applicable to colored and colored diamonds.
Color distribution characteristics: the distribution position and shape of color band are related to cutting shape and irradiation direction. When subatomic particles from cyclotron bombard the round faceted diamonds from the exhibition hall, the illuminated colors can be seen around the exhibition hall in an umbrella shape through the table. In this case, the stepped diamond can only show a rectangular band near the bottom tip. When the crown of the diamond is bombarded, the waist edge of the cut diamond will show a dark ring. When the bombardment comes from the side of the diamond cutter, the color of the cutter near the bombardment source is obviously deepened.
Absorption spectrum: there are 595nm or H 1b and H 1c lines.
Conductivity: The blue diamond formed by radiation has no conductivity. ?
③ Germanium diamond
Also known as high temperature and high pressure repair diamond, the color after treatment is mostly in the range of D to G, but the appearance is slightly foggy, with brown or gray tones instead of yellow tones. Under high magnification, internal texture can be seen, and feather cracks are common, accompanied by reflection. Cracks are often exposed to diamond surface, partially healed cracks, cleavage and abnormal inclusions. This kind of diamond is difficult to identify. General Electric promised that the diamonds they handled would be engraved with the words "GE POL" or "Bellataire" on the waist surface with a laser.
④ Xinxing Diamond
A new color optimization method, also known as high temperature and high pressure enhancement or nova diamond. Diamond has strong plastic deformation, strong abnormal extinction, strong yellow-green fluorescence and chalk fluorescence. These diamonds are engraved with the logo of Nova diamonds, with unique serial numbers and certificates.
[2] Cleaning treatment
① Laser drilling
Traditional laser drilling treatment: permanent laser holes are left on the diamond surface, and because the hardness of the filling material can never be the same as that of the diamond, pits that are difficult to observe are often formed.
KM internal fracture method: this kind of secondary fracture looks similar to natural fracture, but it is easy to break the diamond if this method is not handled properly.
KM internal seam method: centipede-shaped inclusions can be seen on the surface, which are natural bending cracks, and many cracks protrude from both sides of vertical inclusions; There are sporadic black residues in the continuous cracks treated by laser, which are not completely treated.
② Crack filling
Flash effect: it has obvious flash effect, and the common flash colors in the dark are orange yellow, purple red and pink, followed by pink orange. Common flash colors in bright areas are blue-green, green, yellow-green and yellow. Different parts of the same crack can show different flash colors, and the flash color of the filled crack can change with the rotation of the sample.
Flow structure: the flow structure in the process of filling materials often remains in cracks.
Catch bubbles: it looks like a group of fingerprint inclusions, or it may be very small and bright.
Flocculent structure: when the filling material is too thick, it can produce flocculent structure, and sometimes this flocculent structure can evolve into a network structure, which is easy to find.
Micro-cracks: White thin lines are found in some filled cracks, which may be micro-cracks in cracks. This feature is very weak and can only be observed under the strong illumination of fiber-optic lamps.
Filling color: when the filling is thick, you can see the color of light brown to brown or orange. The body color of this filler can only be observed in the filled cavity and laser hole.
Incomplete filling: usually very narrow, it looks like tiny white scratches or scratches under dark areas, which may be caused by removing part of the filling during the steaming of diamonds.
Surface residue: Part of the filler remains on the diamond surface.
[3] Diamond film
Polycrystalline with granular structure on the surface; High-quality DF diamond film is measured by Raman spectrum, and its characteristic peak is around 33,300 px-1,and its full width at half maximum; The frequency shift of the characteristic peak of DF diamond film with poor quality is large, and its intensity is weakened, even a broad peak appears near 37500px- 1.
[4] Divided diamonds
It is made of diamond (as the top layer) and cheap crystal or artificial colorless sapphire (as the bottom layer). Bonding technology is very high, which can be embedded in jewelry to hide bonding, making it difficult to find. When a small needle tip is placed on the table of this gem, you will see two reflection images, one from the table and the other from the joint surface, which is not the case with natural diamonds. Careful observation, no matter what direction, natural diamonds can't be seen through because of reflection and flicker, but diamond assembly is different, because the lower part is a mineral with low refractive index, and the assembled stone has poor reflection ability and can sometimes be penetrated.
2. Identification method of natural diamonds (naked eye identification method is introduced here)
(1) rough identification:
[1] luster: diamond luster, with a "sparkling" appearance.
[2] Appearance and surface characteristics: The common crystal forms are octahedron, rhombic dodecahedron and their aggregates, and there are few minerals with these crystal forms in colorless transparent minerals. In addition, another feature is the spar pattern of diamond, and different crystal faces have different growth line characteristics, such as the common triangular growth line on octahedral crystal faces, and the tip of the triangle points to the edge of octahedral crystal; Cubic crystal faces often have square or rectangular growth lines, which make an angle of 45 degrees with the cubic plane; The crystal plane of rhombic dodecahedron is usually parallel to the long diagonal direction.
[3] Density: natural diamond 3.52g/cm3.
(2) Identification after polishing:
[1] Line experiment: The sample table is placed face down on a piece of lined paper. If it is a diamond, you can't see the lines on the paper.
[2] Tilt experiment: Place the table top in the sample on a black background, observe from the direction perpendicular to the table top, tilt the observer outward, and observe the farthest area on the table top. If a dark window appears, the sample is not a diamond.
[3] Hydrophilicity experiment: The oil-based pen can leave clear and continuous lines on the surface of natural diamonds; On the contrary, when crossing the surface of diamond imitation, ink usually converges into small droplets, and continuous lines cannot appear.
[4] Water retention test: wash the sample thoroughly and drop water on the sample. If the water drops can stay on the surface of the sample for a long time, it means that the sample is a diamond.