Opal is a precious gemstone admired for its unique play of colors and stunning beauty. However, determining the authenticity of opal can be challenging, especially with the prevalence of synthetic and imitation opals in the market. This comprehensive guide will walk you through the characteristics of genuine opals, the different types, and various tests to identify real opal.
Types of Opal
Opal comes in several varieties, each with distinctive features. Understanding these types is the first step in identifying real opal.
1. Precious Opal
Precious opal is known for its play-of-color, a phenomenon where the stone displays a rainbow-like spectrum of colors. This type of opal is the most valuable and sought after. The play-of-color occurs due to the diffraction of light within the silica spheres that make up the opal.
2. Common Opal
Common opal, also known as potch, lacks the play-of-color. It can be found in a variety of colors, including white, gray, black, brown, and more. Although it doesn’t exhibit the same dazzling display as precious opal, common opal can still be beautiful and is often used in jewelry.
3. Fire Opal
Fire opal is typically orange to red and may or may not exhibit play-of-color. The vibrant body color makes it distinctive, and those with play-of-color are especially valuable.
4. Boulder Opal
Boulder opal forms within the crevices of ironstone boulders. It combines opal with the host rock, creating a unique and attractive contrast. The play-of-color can be present in this type of opal, adding to its allure.
5. Black Opal
Black opal is one of the most prized varieties. It has a dark body color that makes the play-of-color stand out more vividly. This type of opal is primarily found in Australia and is highly valued by collectors.
Characteristics of Real Opal
To determine if an opal is real, it’s essential to understand its physical and optical characteristics:
1. Play-of-Color
As mentioned earlier, precious opal exhibits a play-of-color, which is a defining feature. This optical phenomenon should appear as flashes or patterns of various colors when viewed from different angles.
2. Body Tone
The body tone refers to the base color of the opal, ranging from light to dark. Black opals have a dark body tone, while white opals have a light body tone. The body tone affects the visibility and contrast of the play-of-color.
3. Transparency
Opals can be transparent, translucent, or opaque. The transparency can affect the overall appearance and value of the stone. For example, crystal opal is transparent to semi-transparent with vibrant play-of-color.
4. Cut and Shape
Opals are usually cut into cabochons, which are smooth, rounded stones without facets. The cut should enhance the play-of-color and minimize the visibility of any inclusions or imperfections.
5. Inclusions and Imperfections
Natural opals may have inclusions, such as sand or tiny fractures. These imperfections can help identify a real opal, as synthetic opals are often free of such flaws.
Testing Methods to Identify Real Opal
Identifying real opal involves several tests, some of which can be done at home, while others may require professional assistance. Here are the most effective methods:
1. Visual Inspection
A thorough visual inspection is the first step in identifying real opal. Use a magnifying glass or jeweler’s loupe to examine the stone closely. Look for the following:
Play-of-Color: Genuine precious opal should exhibit a play-of-color that changes as you rotate the stone.
Inclusions: Natural opals may contain inclusions like tiny sand particles or organic matter.
Cut and Shape: Check the cut and shape of the opal. Real opals are usually cut as cabochons, with smooth, rounded surfaces.
2. Water Test
The water test can help distinguish between natural opal and some synthetic or imitation opals. Here’s how to do it:
- Fill a glass with water.
- Place the opal in the water.
- Observe the opal for any changes.
Natural opals will generally not show significant changes when submerged in water. However, some synthetic opals may exhibit a mosaic pattern or layers, indicating they are not genuine.
3. Light Test
The light test involves observing the opal under different lighting conditions. Real opals should display play-of-color under both natural and artificial light. Follow these steps:
- Hold the opal under a bright light source.
- Rotate the opal and observe the colors.
- Repeat the test under natural daylight.
Genuine opals will show consistent play-of-color under both types of lighting.
4. Specific Gravity Test
The specific gravity test measures the density of the opal, which can help distinguish between real opal and some imitations. This test is more complex and may require specialized equipment:
- Weigh the opal in air using a precise scale.
- Weigh the opal while submerged in water.
- Calculate the specific gravity using the formula: Specific Gravity = (Weight in Air) / (Weight in Air – Weight in Water).
Natural opals typically have a specific gravity between 1.98 and 2.25.
5. UV Light Test
Under ultraviolet (UV) light, some opals may fluoresce, showing a different color or brightness. This test can help identify synthetic opals, which may fluoresce differently from natural opals. Use a UV lamp and observe the opal in a dark room:
- Place the opal under the UV light.
- Observe any fluorescence.
- Compare the fluorescence with known standards for natural and synthetic opals.
6. Heat Test
The heat test involves applying mild heat to the opal to observe its reaction. Natural opals may show minor changes, but synthetic opals, especially those made from plastic, may react differently. Use caution with this test to avoid damaging the opal:
- Gently heat the opal using a hairdryer or warm water.
- Observe any changes in color or appearance.
- Avoid using an open flame, which can damage the opal.
7. Professional Gemologist Evaluation
For a definitive identification, consider consulting a professional gemologist. They have access to advanced tools and techniques, such as spectroscopy and microscopy, to accurately identify real opals. A gemologist can provide a certificate of authenticity, which is valuable for high-value opals.
Common Misconceptions About Opals
Several misconceptions surround opals, which can lead to confusion when trying to identify real opals. Here are some common myths and the truth behind them:
1. Opals Are Fragile and Easily Broken
While opals are softer than some other gemstones, they are not excessively fragile. Proper care and handling can prevent damage. Avoid exposing opals to extreme temperature changes and harsh chemicals.
2. Synthetic Opals Are Identical to Natural Opals
Synthetic opals can mimic the appearance of natural opals, but they have distinct differences. Synthetic opals may exhibit a more uniform pattern and lack natural inclusions. They are also often less valuable than their natural counterparts.
3. All Opals Are Expensive
The price of opals varies widely based on type, quality, and size. Common opals and some varieties of fire opal can be affordable, while high-quality black opals and boulder opals can be quite expensive.
4. Opals Are Unlucky
The belief that opals are unlucky is a superstition with no factual basis. Opals have been treasured throughout history for their beauty and unique properties.
Conclusion
Determining if an opal is real requires a combination of visual inspection, simple tests, and professional evaluation. Understanding the characteristics of different types of opals and knowing what to look for can help you identify genuine opals and appreciate their beauty. Whether you’re a collector, jeweler, or enthusiast, this guide provides the knowledge needed to distinguish real opal from synthetic or imitation stones. Always consider consulting a professional gemologist for high-value opals to ensure their authenticity and value.
FAQs
Are all opals valuable?
The value of opals varies depending on factors such as type, quality, size, and the presence of play-of-color. While some opals, such as high-quality black opals, can be highly valuable, others, like common opals, may be more affordable.
How do synthetic opals differ from natural opals?
Synthetic opals are man-made and are created to mimic the appearance of natural opals. They may exhibit a more uniform pattern, lack natural inclusions, and often have a lower value compared to natural opals. Synthetic opals can sometimes be identified through visual inspection and certain tests.
Are opals fragile?
While opals are softer than some other gemstones, they are not excessively fragile. With proper care and handling, opals can last a lifetime. Avoid exposing opals to extreme temperature changes and harsh chemicals to prevent damage.
Is the water test reliable for identifying real opal?
The water test can help distinguish between natural opals and some synthetic or imitation opals. However, it may not be foolproof, and other tests, such as the light test and specific gravity test, should also be conducted for a more accurate assessment of opal authenticity.