Overview


Turquoise, with its unique blue and green hues and rich cultural heritage, is deeply cherished by many. However, the market is flooded with various types of treated turquoise, and even imitations. These treatments aim to improve the color, hardness, density, and luster of turquoise to enhance its commercial value. As a seasoned gemstone appraisal expert, I will provide a detailed guide on how to identify treated turquoise, helping you avoid pitfalls and acquire genuine natural turquoise.

Fundamental Knowledge


Before delving into identification methods, we must first understand the natural characteristics of turquoise and common treatment methods.

Characteristics of Natural Turquoise:
* Color: Sky blue, light blue, blue-green, green, yellowish-green, etc. Color distribution is often uneven, frequently accompanied by matrix (black or brownish veins).
* Luster: Waxy to vitreous luster, with an earthy luster on fractured surfaces.
* Hardness: Mohs hardness 5-6, relatively soft.
* Density: 2.6-2.9 g/cm³.
* Structure: Commonly cryptocrystalline, fine and dense, with some visible microcrystals.
* Water Absorption: Possesses a certain degree of water absorption; color deepens upon contact with sweat or oils, a phenomenon known as 'patina' or 'bao jiang'.

Common Treatment Methods:

  • Resin Impregnation (Stabilization/Filling): Soaking turquoise in colorless or colored resin to fill pores, thereby increasing hardness, density, luster, and improving color uniformity.

  • Dyeing: Soaking light-colored or whitish turquoise in dyes to achieve vibrant blue or green colors.

  • Waxing/Oiling (Optimization): Similar to resin impregnation, but usually refers to a light resin treatment for higher-quality turquoise to enhance its stability.

  • Color Alteration (Densification Optimization): Changing the color of turquoise through chemical or physical methods to make it more appealing.

  • Reconstruction (Reconstituted): Mixing crushed turquoise fragments or powder with a binder and pressing them into shape. This is strictly an imitation.

  • Filling: Filling cracks or pits in turquoise with resin.


Identification Methods (Step-by-Step)


Identifying treated turquoise requires a comprehensive approach, moving from macroscopic to microscopic observations.

Step One: Visual Inspection (Macroscopic Features)


This is the most basic and crucial step, requiring careful observation of the overall appearance of the turquoise.

  • Color:

* Natural Turquoise: Color is typically uneven, with variations in shade, often accompanied by naturally formed matrix (black or brownish veins), whose edges are clear and natural. Color transitions are natural and layered.
* Dyed Turquoise: Color is overly uniform, unnaturally vibrant, and lacks depth. Dyes may accumulate in cracks or depressions, appearing overly dark. Wiping with a cotton swab dipped in acetone or alcohol may cause color transfer (Caution: This method can be damaging, use with care).
* Resin-Impregnated Turquoise: Color may be uniform, but the surface luster often appears excessively 'shiny' or 'plastic-like'.
* Case Study: Figure 1 shows a piece of natural high-grade turquoise with varying shades of color and natural, flowing matrix. Figure 2 displays a piece of dyed turquoise, with overly uniform color and dye accumulation in cracks.

  • Luster:

* Natural Turquoise: Waxy to vitreous luster, with a warm, moist texture.
* Resin-Impregnated Turquoise: The surface often exhibits a resinous luster, sometimes appearing overly oily or plastic-like, lacking the natural warmth.
* Reconstituted Turquoise: Surface luster is dull, sometimes showing fine granular structures.

  • Surface Features:

* Natural Turquoise: The surface typically has fine pores, slight unevenness, or natural textures, but is generally smooth.
* Resin-Impregnated Turquoise: The surface may be very smooth and flat, even having a 'jelly-like' appearance. Under magnification, tiny bubbles or flow lines of the resin may be visible.
* Reconstituted Turquoise: Fine granular structures may be visible on the surface, sometimes showing layered or swirling textures formed during the pressing process.
* Case Study: Figure 3 shows the microscopic surface of natural turquoise, with visible fine natural pores. Figure 4, in contrast, clearly displays the surface of resin-impregnated turquoise, with excessively uniform luster, and at certain angles, traces of resin infill are visible.

Step Two: Tactile Sensation and Hardness Test (Auxiliary Judgment)

  • Tactile Sensation:

* Natural Turquoise: Feels warm and cool to the touch.
* Resin-Impregnated Turquoise: May feel 'sticky' or 'plastic-like' to the touch, sometimes feeling lighter than natural turquoise.

  • Hardness Test (Use with Caution):

* Natural Turquoise: Mohs hardness 5-6; a light scratch with a knife or steel needle will not easily leave a mark (for high-grade turquoise).
* Resin-Impregnated Turquoise: Hardness may be higher, but scratches will appear plastic-like, curling, or powdery. It is not recommended to perform this test on finished products to avoid damage.

Step Three: Magnification Observation (Microscopic Features)


Use a 10x or 20x magnifying glass to carefully observe the details of the turquoise.

  • Pores and Cracks:

* Natural Turquoise: Natural fine pores are visible on the surface and in cracks, with natural pore edges.
* Resin-Impregnated Turquoise: In pores or cracks, clear or translucent resinous filler may be seen, sometimes with tiny bubbles. The edges of resin-filled cracks will appear rounded or lustrous.
* Dyed Turquoise: Dyes will concentrate in cracks and pores, appearing darker and distributed in a net-like pattern.
* Case Study: Figure 5 shows the pores of natural turquoise under magnification, with natural pore walls. Figure 6 clearly shows the resin filler in the cracks of resin-impregnated turquoise, as well as tiny bubbles within the resin.

  • Matrix:

* Natural Turquoise: Matrix is natural and flowing, tightly integrated with the turquoise body, with clear edges. The matrix itself may also have fine pores.
* Resin-Impregnated Turquoise: Matrix may be encased in resin, making its edges appear blurry or reflecting light from the resin.
* Dyed Turquoise: Some dyed turquoise may imitate matrix, but it usually appears stiff, unnatural, or overly uniform in color.

Step Four: Professional Instrument Testing (Final Confirmation)


For samples that are difficult to judge, professional instruments are required for testing.

  • Fourier Transform Infrared Spectrometer (FTIR): This is the most effective method for identifying resin-impregnated turquoise. The infrared spectra of natural turquoise and resin are significantly different, allowing for clear detection of resin presence.

  • Ultraviolet Fluorescent Lamp: Some resin-impregnated turquoise will fluoresce under UV light, while natural turquoise usually has no or weak fluorescence. However, this method is not absolute, as some resins do not fluoresce.

  • Density Test: Accurately measure the sample's density and compare it with the density range of natural turquoise. Resin-impregnated or reconstituted turquoise may have lower or higher densities.


Common Misconceptions

  • 'High-grade' (Gao Ci) means resin-impregnated: Not true. High-grade turquoise refers to natural turquoise with dense texture, high hardness, and good luster, which is highly valuable. While resin impregnation can improve luster, it lacks the natural warmth.

  • Presence of matrix means natural: Matrix is a natural feature of turquoise, but some dyed or reconstituted turquoise may also imitate matrix. It is necessary to combine other features for comprehensive judgment.

  • Using fire for identification: This method will severely damage turquoise and is not recommended. Resin-impregnated turquoise will emit a burnt smell and melt when heated, but natural turquoise will also change color or even crack due to high temperatures.


Practical Tips

  • Observe and Compare Frequently: Regularly examine images and physical examples of natural turquoise to develop an 'eye' for natural characteristics.

  • Purchase from Reputable Sources: Choose reputable dealers or qualified jewelry stores and request authoritative appraisal certificates.

  • Pay Attention to Details: For any piece of turquoise, regardless of size, carefully observe its color, luster, surface texture, pores, matrix, and other details.

  • Send for Testing if Doubtful: When in doubt about the authenticity or treatment of turquoise, the safest approach is to send it to a professional gemological testing laboratory for appraisal.

  • Beware of 'Perfection': Natural turquoise will more or less have some natural flaws. Turquoise that is overly perfect, flawless, and unnaturally uniform in color often warrants increased suspicion.


Conclusion


Turquoise identification is a discipline that requires systematic learning and extensive practice. By combining visual inspection, tactile sensation, microscopic analysis with a magnifying glass, and necessary professional instrument testing, we can effectively identify treated turquoise. Remember, the beauty of natural turquoise lies in its unique natural patterns and warm texture, and while treatments can improve its appearance, they cannot imbue it with the natural spirit and collection value. I hope this tutorial helps everyone become more confident and discerning on their journey of collecting and purchasing turquoise. May you all find the natural turquoise you desire!