Selection and maintenance skills of variable stone 0 1 and color (including discoloration effect)
Bright, pure and uniform colors are required, and the discoloration effect is obvious. Most people tend to be green, blue, brown and red? Blurred? Mixed colors, thus showing a less obvious discoloration effect, generally dark green during the day and reddish brown under the light at night, that is, green tourmaline during the day and pomegranate red at night. Metamorphic rocks with too light color can't meet the quality requirements of high-quality gemstones. Stones that are too dark have no brightness and are almost black.
02, clarity
For the variable stone without cat's eye effect, it is required to be pure and flawless, with excellent transparency. Metamorphic rocks often contain almost no inclusions, but there are often many cracks, especially in the Urals Mountains of Russia. A high degree of clarity will improve the value of stones, especially those with good discoloration effect. Therefore, the color change effect is good, and the value of pure stone with strong color will increase greatly.
Metamorphic rocks with cat's eye effect may contain inclusions, and the transparency is translucent to slightly transparent. When some types of slender inclusions are oriented parallel to each other, an additional phenomenon called cat's eye effect can be produced, which will also increase the value of rock replacement. However, it is extremely rare to combine the beautiful cat's eye effect with the discoloration effect.
03, cutting work
For variable stones without cat's eye effect, the most common ones are processed into so-called round, oval, pear-shaped and square-cushion-shaped mixed cuts, that is, Guanliangge steps, and emerald cuts. Bright cuts have kite-shaped and triangular facets, while step cuts have a concentric arrangement of parallel facets.
The variable stone has a strong polychromatic color, which means that it can display different colors when viewed from different directions. Usually, its three colors are green, orange and purplish red. However, the remarkable discoloration effect is not necessarily due to the polychromatic color of gemstones, but depends on the unusual light absorption characteristics of minerals.
The variety of colors of variable stones is very challenging for cutting and polishing craftsmen. When processing variable gemstones, the cutter must orient the gemstone so that it presents the strongest discoloration effect through the crown. It is very important to determine the position of the original stone. When the table faces the observer, the finished gem appears purple and green.
For metamorphic rocks that may have cat's eye effect, directional cutting and grinding are carried out according to the distribution of inclusions, and the metamorphic rocks are cut into arcs (for the sake of care, the bottom is generally not polished), which can show cat's eye effect under the irradiation of strong light or point light source. It is best to cut and polish it into a cambered shape with a suitable height (the camber is too high or too low, the proportion is out of balance, it is not beautiful, the camber is too high, it is difficult to inlay, there is too much useless weight, and the cost performance is not good; If the camber is too low, the cat's eye effect is not obvious), so that the cat's eye effect is obvious and parallel to the long axis direction.
04, carat weight
Most metamorphic rocks are small, weighing less than 1ct, usually 0.3~0.4ct, and those larger than 5ct are very rare, especially the exposed metamorphic rocks produced in Russia exceed 10ct. In the size of metamorphic rocks, large metamorphic rocks are less, so the price is more expensive. Larger size and better quality, its price has risen sharply.
05. Origin
In the past, the mineral deposits in the Urals Mountains in Russia, the main producing area of metamorphic rocks, have almost dried up. At present, the main producing areas of metamorphic rocks are Sri Lanka, Brazil, Madagascar and Tanzania, and others are Myanmar, India, Zimbabwe, the United States and Tasmania.
The color or discoloration effect of metamorphic rocks from different producing areas is quite different. At present, the variable gemstones produced by Russian mines are very limited, which means that the number of colorful gemstones they produce cannot exceed 200 years ago, so it is more difficult to obtain. The color of metamorphic rocks in Brazil is comparable to that in Russia, but the output in Brazil is declining.
Metamorphic rocks in Sri Lanka are generally larger than those in Russia, but the color is often not ideal. Compared with the blue-green color of Russian metamorphic rocks, the green color of metamorphic rocks in Sri Lanka tends to be yellow, and its red color is typical maroon rather than purple. In other words, the color saturation of green and red is low, which makes them slightly brown.
In short, when buying a stone, observe its color and its changing effect with a pen flashlight, depending on the number of defects, the quality of cutting or the strength of fire color and the size of particles. As for the place of origin, it is still based on quality.
If you want to buy your favorite stone, you'd better know some skills:
First, correctly use the name of the stone.
According to the national standard (GB/T 16552-20 10), only gem-grade gold emeralds with color-changing effect can be directly called? Change stones? Without any embellishment. Other gemstones with color-changing effect must be in front? Discoloration? Color-changing spinel, color-changing fluorite and other two characters. It is forbidden to use two or more natural gems named after them, such as? Ruby spinel? 、? Gems and sapphires? , but? Stone cat's eye? Except ...
The second is not to be confused with similar gems.
From the appearance, metamorphic rocks are easily confused with color-changing garnet, color-changing sapphire, color-changing spinel, color-changing fluorite, color-changing kyanite, color-changing monazite and andalusite. Andalusite is strongly polychromatic, similar to metamorphic rocks. The key to identification is the difference of color change effect, inclusion characteristics, refractive index and infrared spectrum. A trained gemstone appraiser can easily distinguish these gemstones according to their optical properties, such as polychromatic color, polarization, refractive index, birefringence and color-changing effect. ) and physical properties (hardness, density and cleavage, etc. ), so consumers don't have to worry about it.
Third, be careful to synthesize metamorphic rocks.
As early as 1985 years ago, the methods of synthesizing metamorphic rocks by flux method and Czochralski method appeared, and then the method of hydrothermal synthesis of metamorphic rocks appeared. The difference between synthetic metamorphic rocks and natural metamorphic rocks is that synthetic metamorphic rocks produced by different methods all contain different types of characteristic inclusions, and the characteristics of trace elements, refractive index and fluorescence are slightly different. The latest research shows that infrared spectroscopy can distinguish natural metamorphic rocks from synthetic metamorphic rocks without damage, quickly and effectively, especially for high-grade metamorphic rocks without inclusions.
Note that, according to the data of GIA, synthetic stones in the jewelry market are generally made with the name of the sales company and? Created? Not synthetic. For example, in recent years, Japan has successfully synthesized a stone cat's eye. What is its sales name? Kazuo inamori (kazuo inamori)? . Consumers should be especially careful when purchasing, and don't be afraid of omission. You can ask the merchant to show the appraisal certificate or go to a regular jewelry appraisal agency for testing.
Fourth, beware of imitation stone.
In the jewelry market, synthetic color-changing sapphire, synthetic color-changing spinel, red garnet and red glass are sold as natural stones. The difference is that natural metamorphic rocks have strong trichromaticity, gas-liquid two-phase inclusions, refractive index 1.747 ~ 1.756, and density of 3.73g/cm3. However, the synthetic color-changing sapphire has only dichroism, with a refractive index of 1.762 ~ 1.770 and a density of 3.99g/cm3, while the synthetic color-changing spinel has no polychromatic color, with a refractive index of 1.728 and a density of 3.64 ~ 3.99 g/cm3, both of which have arc bands. In particular, the discoloration effect is obviously different. Artificial sapphires are not green but blue in sunlight, and purple and blue in candlelight.
Wear stone-changing maintenance cheats.
Variable stone is a beautiful, rare and durable gem. Metamorphic rocks are relatively hard, with Mohs hardness of 8.5, excellent toughness and no cleavage, and will only break when they are hit. Very suitable for inlaid jewelry such as inlaid rings worn every day.
The metamorphic rock has good stability, heat resistance, light resistance and resistance to common chemicals, and there is no risk in normal wear.
clean
Metamorphic rocks are chemically stable, so it is always safe to clean them with warm soapy water. Even using ultrasonic and steam cleaners is usually safe.
Variable stone is also one of the few pure natural gems without any optimization treatment. Stone jewelry filled with cracks or inlaid with thin metal can only be cleaned with warm soapy water.
deposit
Although the stone is hard and durable, it is still easy to be scratched by other harder gems. Therefore, be careful not to mix stone jewelry and its artwork with any gems and jewelry with hardness higher than it, so as not to cause scratches.