最近有客戶送驗一顆藍寶石至本所，經過拉曼光譜儀確認為藍寶石，正面觀察可見色帶且顏色偏灰藍，頗為自然。下鏡觀察後，三位鑑定師確認其為天然藍寶與合成藍寶石雙層石。這種雙層石是由天然藍寶磨成的冠部與合成藍寶磨成的亭部拼合而成。因為天然藍寶石價高且早期工資便宜，遂出現這類仿品，因其正面觀察色澤自然，遠比一般過於完美鮮豔的合成藍寶石更易於騙過珠寶商的眼睛。然而，現今的切磨工資昂貴，這類型的仿品已不再生產，市面上流通的數量極少，多為早期製作留存的樣本，真可說是僅存於教科書上，以走入歷史的造假技術。這類的紅藍寶仿品雖已不多見，但是很容易打眼，為求謹慎消費者應該找可信賴的鑑定所確認。如果無法即時送驗，當下要怎麼避免買到這類夾層石仿品呢？
- 側15度角肉眼觀察，冠部與亭部的顏色通常不同，可能是深淺差異、彩度差異、色相差異或甚至有色與無色的差別。
- 顯微鏡或放大鏡下可見冠部有天然內含物(指紋狀物、羽裂紋)，亭部有人造內含物(氣泡、生長弧線)，中間有膠合面(膠、氣泡)。
A sapphire was sent to TULAP for certificate which looks like natural sapphire and got the characteristic raman spectrum of corundum. After microscopic observation, TULAB gemologists confirm that the stone was sapphire and synthetic sapphire doublet. This is a classic imitation for natural sapphire; it was made of natural-sapphire crown and synthetic-sapphire pavilion. For its natural appearance and color, the doublet is not easy to tell by jewellers. However, this kind of imitation is no longer in production for high its cost. The doublet is rarely seen now; it has been a classic imitation on gemology textbook. How to avoid this imitation gem? Follow the following 2 tips:
- By lateral observation(15° tilt), crown and pavilion is usually different in color.
- By microscope or magnifier, there might be natural inclusions(fingerprint, feather…) in crown and artificial inclusions(bubbles, curved striation) in pavilion and the contact surface in the girdle(resin, bubble).
雙層石正面顏色與外觀極為自然
The color and appearance of doublet is very natural(greyish blue with color zoning)
側向觀察冠部與亭部顏色明顯不同
By lateral observation, crown and pavilion shows different color.
顯微檢查下可見亭部氣泡、生長弧線，腰部有接著面且接著面上有膠和氣泡。
Under magnification, there are curved striation and bubbles in the pavilion; contact surface on the girdle; bubbles and resin on the contact surface.
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