Ngọc trai có 2 loại cơ bản là Ngọc trai nước mặn, Ngọc trai nước ngọt. Còn một loại thứ 3 nữa là Ngọc trai giả (Ngọc Trai nhân tạo) làm bằng Vỏ Ốc, bằng plastic… được phủ bên ngoài bằng 1 lớp sơn hoặc bột ngọc trai
Ngọc trai nước mặn lại chia ra các loại sau:
- Ngọc trai đen do giống trai Margaritifera tạo ra, được nuôi cấy và phát triển đa số ở tại đảo quốc Tahiti thuộc nước Pháp. Tên gọi thương mại là ngọc trai Tahiti.
- Ngọc trai vàng ánh kim do giống trai Pinctada tạo ra, được nuôi cấy và phát triển tại vùng biển nam Thái Bình Dương. Tên gọi thương mại là ngọc trai South Sea.
- Ngọc trai trắng, vàng chanh được nuôi cấy và phát triển nhiều ở Nhật bản. Tên thường gọi là ngọc trai Akoya.
Ngọc trai nước ngọt cơ bản chỉ có màu trắng và vàng chanh, giá lại rẻ hơn rất nhiều, giá chỉ bằng 1/10 gọc trai nước mặn tùy giám định. Thời gian khai thác của ngọc trai nước ngọt nhân tạo ngắn chỉ hơn 1 -2 năm là có thể khai thác.
Ngọc trai biển là loại ngọc quý được “sinh ra” từ vật thể sống dưới đáy Đại Dương, với kích thước và màu sắc hoàn toàn tự nhiên
Ngọc trai giả ngày xưa được làm từ nhựa, thủy tinh được phủ sơn và dầu bóng. Ngày nay, ngọc trai giả còn được phủ một lớp mỏng xà cừ, tạo sự óng ánh và độ phản chiếu ánh sáng gần giống với ngọc trai thật. Cao cấp hơn, nhiều nơi còn làm ngọc trai giả từ bột xà cừ tổng hợp lấy từ vỏ con trai, gây khó khăn trong việc phân biệt. Sản phẩm ngọc trai giả có nhiều kiểu dáng và màu sắc phong phú
Những cách có thể phân biệt ngọc trai thật và giả :
1. Ánh nắng mặt trời
Khi ra ngoài ánh nắng mặt trời, ngọc trai biển có khả năng phản chiếu ánh màu ngũ sắc. Chỉ có ngọc trai biển mới phản chiếu ánh màu ngũ sắc.
2. Sử dụng Kính Soi
Khi nhìn dưới kính soi ngọc học từ 50x đến 70x, dễ dàng nhìn thấy bề mặt viên ngoc trai thật hình vảy, hoặc trông giống một mê cung (do hiện tượng tế bào xà cừ xếp lớp), trong khi ngọc trai giả thì bề mặt lấm tấm hạt.
3: Máy X-quang chụp xuyên tâm
Khi chụp X-quang sẽ thấy rất rõ hình ảnh ngọc trai thật có hạt nhân và lớp xà cừ dày bao quanh hạt nhân. Còn ngọc trai giả chỉ có một lõi đặc bằng nhựa, có hoặc không có một lớp xà cừ phủ bên ngoài rất mỏng.
Hình ảnh X-quang cho thấy rất rõ viên ngọc trai thật có nhân và lớp xà cừ dày 1.2mm (trái) trong khi ngọc trai giả hoàn toàn không hề có nhân, và hấp thụ tia sáng của máy X-quang rất tốt.
4: Quan sát xung quanh lỗ khoan ngọc trai
Xung quanh lỗ khoan viên ngọc trai giả dễ bị bong tróc lớp sơn có thể quan sát ngay bằng mắt thường.
5: Kiểm tra bằng răng
Chà nhẹ viên ngọc trai lên răng. Nếu cảm thấy trơn tru là ngọc trai giả. Trái lại nếu thấy rin rít, nhám, thô, có thể là ngọc trai thật.
Cắn nhẹ viên ngọc với một áp lực nhỏ. Ngọc trai giả sẽ dễ bị trầy xước, bong tróc lớp phủ. Trong khi đó, ngọc trai thật có cấu trúc chắc chắn với lớp xà cừ dày hơn sẽ không bị hủy hoại bởi một áp lực khiêm tốn như vậy. Không khuyến khích vì kết quả mang tính tươn đối.
6: Ma sát 2 viên ngọc.
Cách làm này có thể dùng để phân biệt ngọc trai thật với loại ngọc trai giả phủ sơn. Khi chà xát hai viên ngọc với nhau, ngọc trai thật sẽ để lại dư lượng bột rơi ra từ lớp xà cừ phủ bên ngoài. Các loại ngọc trai thật dù mang màu sắc gì, khi ma sát tạo ra bột, bột vẫn luôn là màu trắng…
7: Kiểm tra bề mặt ngọc
Quan sát những chi tiết bên ngoài viên ngọc về hình dạng, độ bóng, kích thước, và màu sắc.
Ngọc trai biển có độ bóng sáng đẹp, màu sắc tự nhiên, bề mặt thường không hoàn hảo.
Ngọc trai giả được sản xuất công nghiệp nên kích thước và hình dạng y như nhau, bề mặt láng bóng không tỳ vết. Hiện nay, nhằm qua mắt khách hàng, nhiều nơi cũng đã cố tình tạo bề ngoài của ngọc trai giả có những khiếm khuyết y như ngọc trai biển.Màu sắc óng ánh được giả tinh xảo, gây lóa mắt người dùng..
8: Thử lửa
Dùng lửa đốt, viên ngọc trai giả phủ sơn sẽ bốc khói đen và bong tróc lớp sơn ngoài. Hoặc có thể đốt nhanh bề mặt viên ngọc qua ngọn lửa, ngọc trai thật sẽ không bắt lửa. Tuy nhiên cách này chỉ dùng để kiểm chứng đối với viên ngọc nhựa
9: Chạm và cảm nhận
Ngọc trai thật khi chạm vào những vùng da nhạy cảm như mí mắt hoặc da mặt sẽ có cảm giác mát, trơn, và nặng tay khi cầm. Ngọc trai giả thường nhẹ hơn, và không có cảm giác nhiệt như ngọc trai thật.
Đối với một số loại ngọc giả tinh vi hơn, mô phỏng đến gần 90% cấu tạo ngọc trai thật thì cần đến các chuyên gia giám định hoặc một số máy móc chuyên dụng mới có thể phân biệt được.
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