Spotting a fake star ruby requires careful observation of its unique characteristics, particularly its natural imperfections and the asterism phenomenon. Genuine star rubies exhibit a distinct six-ray star that glides across the stone's surface when illuminated, but their natural formation also means they are rarely flawless.
Understanding Natural Star Ruby
A star ruby is a rare variety of ruby that displays a phenomenon called asterism, where a six-rayed star appears to float on its surface. This star is caused by reflections from tiny, needle-like rutile inclusions (often called "silk") that are oriented in three specific directions within the crystal structure. This natural occurrence makes each genuine star ruby unique.
Key Indicators for Authenticity
To differentiate a natural star ruby from a synthetic or treated one, look for the following signs:
1. Examine Internal Imperfections and Inclusions
- Natural Flaws: First look for imperfections within the stone. Natural star rubies almost always possess internal characteristics that are signs of their natural origin. These can include:
- Unevenness: The bottom of the stone might show unevenness.
- Color Zoning: Look for stripes or lines of color, where the color is not uniform throughout the gem.
- Growth Lines: Fine lines or patterns that reflect the crystal's growth.
- Minute Inclusions: Tiny crystals, "silk" (rutile needles), or gas bubbles. These imperfections often show through the top surface of the gem, revealing its natural character.
- Significance: Almost all natural star rubies have one or more of these natural imperfections. Synthetics, in contrast, are often too perfect, lacking these natural flaws, or may contain unnatural inclusions like curved growth lines or large, round gas bubbles.
2. Analyze the Asterism (The Star Itself)
- Movement and Sharpness: Then look at the star itself. The star on a natural ruby should appear to glide smoothly across the surface when you move the light source or rotate the stone.
- Natural Star: The rays should be relatively soft, somewhat diffused, and may not be perfectly symmetrical or complete. It will appear to be within the stone, with a three-dimensional quality. It also shows through the top when illuminated.
- Fake Star: A star that looks painted on, overly sharp, perfectly symmetrical, or static (doesn't move) is often artificial. Sometimes, a star is created by carving or laser etching the back of a flat stone, which makes the star appear flat and unchanging.
- Light Source Test: Use a single, strong light source (like a penlight). A natural star will be clear and centered under this light. If the star is visible from multiple angles or under diffused light, it could be fake.
3. Observe the Back of the Stone
- Unevenness and Roughness: The back of a natural star ruby is often unpolished or uneven, reflecting its rough origin and how it was cut to best display the star.
- Color Treatment: Some stones are dyed or have a painted back to enhance color or create a star effect. Look for signs of uneven color distribution or a patchy appearance on the back.
4. The "Shows Through the Top" Principle
This principle applies to two aspects:
- Visible Imperfections: As mentioned, natural imperfections like unevenness, color stripes, or inclusions are often discernible through the top facet of the ruby, indicating its organic growth.
- Star Phenomenon: The six-ray star itself shows through the top surface of the gem when properly illuminated, as it is a surface-level optical effect caused by internal inclusions.
Natural vs. Synthetic/Treated Star Ruby Comparison
| Feature | Natural Star Ruby | Synthetic/Treated Star Ruby |
|---|---|---|
| Imperfections | Often contains natural inclusions (silk, color zoning, growth lines, unevenness on bottom). Visible through the top. | Usually flawless or has unnatural inclusions (curved striae, large bubbles). |
| The Star | Soft, slightly diffused, moves smoothly, may be incomplete/imperfect. Three-dimensional appearance. | Sharp, perfectly symmetrical, often static or moves unnaturally. Flat appearance. |
| Color | Can vary in intensity, often with color zoning. | Usually uniform and intense, sometimes unnaturally vibrant. |
| Body Stone | Ruby is natural. | Ruby is laboratory-grown or treated. |
| Cost | Significantly higher. | Considerably lower. |
| Back Surface | Often unpolished, uneven, or shows natural contours. | Typically uniform and polished, unless a specific treatment is applied. |
Advanced Testing Methods
For definitive identification, especially with high-value stones, a professional gemologist will use:
- Magnification (10x Loupe): To examine internal inclusions, growth patterns, and the nature of the star. Natural silk looks like fine needles; fake stars might show etched lines or a patterned base.
- Refractive Index (RI): A natural ruby's RI is typically 1.76-1.77. Synthetics may have slightly different readings.
- Specific Gravity (SG): Natural ruby SG is around 4.00.
- Spectroscope: To analyze the light absorption spectrum, which can reveal different trace elements present in natural vs. synthetic stones.
- Fluorescence: Natural rubies often fluoresce under UV light, but this can vary. Some synthetics also fluoresce, so this test is not conclusive on its own.
When in Doubt, Consult an Expert
If you are unsure about a star ruby's authenticity, especially for a significant purchase, always consult a certified gemologist or a reputable gemological laboratory like the Gemological Institute of America (GIA) or the International Gem Society (IGS). They have the expertise and equipment to provide an accurate assessment.
