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Evaluation factors of ruby: color, clarity, weight

Evaluation factors of ruby: color, clarity, weight

June 24, 2021

Ruby

In the photo: ruby from Burma weighted 2.56 ct. No treatment.

From this article you can study information about features of various factors, that a person buying a natural ruby need to pay attention. Given practical recommendations will help to choose a nice good quality sample.

Ruby is a precious stone, red corundum variety. it Is a «brother» of sapphires in chemical composition and structure. Ruby is the most approciated colored stone. The best samples can compete in price with very expensive fancy diamonds. For example, in May 2015, an unheated Burmese red ruby weighted 25.59 carats was sold at Sotheby’s for $ 30.3 million. This is a record for the total cost and a record cost per carat – $ 1,185,451 / ct.

In this part of the article, we consider three main factors affecting value of a stone: color, its clarity and weight. In the second part, we consider such factors as cutting a ruby, its deposits, etc., affecting pricing. And tell you about interesting varieties. In the third part, we show you the real prices for a ruby per carat.

Color

Among all factors firstly color affects beauty of rubies. Rubies color range contains a red color with shades of pink, purple or orange. The most valued color is pure spectral red. In commerce, the phrase “Pigeon’s Blood” is used to refer to bright red of a ruby. Such a color can also be specified in certificates on ruby as a commercial one.

ruby etalons of red «Pigeon’s blood» from the collection of GIT

In the photo: ruby etalons of red «Pigeon’s blood» from the collection of GIT

In GRS laboratory opinion, «Pigeon’s blood» rubies possess from medium to strong red fluorescence, there are a large amount of Cr and a small amount of Fe (which dampens fluorescence). Due to red fluorescence, that appears in UV rays, these rubies in sunlight show the brightest red color. Natural rubies look best in bright sunlight or incandescent yellow light. Due to such lighting, red color of a ruby becomes even more saturated. In white daylight, color fades, and even not very dark rubies sometimes look brownish. These features foreign sellers keep in mind during making lighting in their stores and windows. For many rubies from the royal treasures bright scarlet color is characterized, which is now very rare. Interesting, that there is no consensus among gemologists where a clear border in color between pink-red rubies and pink sapphires is (both of them are varieties of corundum).

In the photo: red ruby grading, the collection of GIT. Color «Pigeon’s blood» refers for vivid red ruby only.

In the majority of jewelry stores you can see small light pinkish-red corundum of the lowest quality. Such cheap stones are not to be compared with the best bright red natural samples.

Choosing stone, pay attention to color distribution in a sample. Red color sometimes looks as uneven spots or areas. For real rubies, as well as for sapphires presence of color zoning is typical, that looks like alternation of light and dark stripes in a stone at an angle of 120 degrees.

“Practical advice.  Judging a color is a cornerstone of choosing a natural ruby, you should like it. Better view a stone in different lighting, in daylight, outdoors or near a window, in various lamps, shine white or yellow flashlight. Note, how a sample is light or dark, pay attention on its saturation, whether the spotting or zoning is visible from a table of a stone. Choose no dark, bright stones that look good in different lighting conditions.“

Clarity

rough ruby from Tajikistan

In the photo: rough ruby from Tajikistan. Because of low clarity such stones goes on cabochons making

Besides color, grade of clarity can affect beauty. It is defined as amount of inclusions and cracks and how much they are visible to a naked eye, or when looking at a 10-fold loupe. Rubies are rare and expensive gems, therefore, due to uniqueness of clean faceted samples, they often have cracks and inclusions. They are characterized by presence of light needle inclusions of rutile or boehmite. Large accumulations of such inclusions can create cloudy areas in a stone. Also, solid inclusions, such as apatite or zircon sometimes present in a stone. Рresence of inclusions may not affect the perception of beauty of a stone, if they are not striking and too contrast.

If a natural ruby has a beautiful color, then clarity can not be judged very strictly. But if it has perfect clarity grade, then it can be whether a very rare and expensive real ruby or very cheap synthetic corundum. For eye clean stones, it is better to ask the seller for a certificate from an independent gemological laboratory that confirms its natural origin. Rubies with poor clarity and transparency are usually procecced in the form of a cabochon. Also, opaque pieces of rough ruby can be used to make carvings.

two untreated Burmese rubies

In the photo: two untreated Burmese rubies. Left stone contains more inclusions and cracks, than right one. Due to better transparency the right sample also reflects light from pavilion facets and it will be more interesting in dynamic.

“Practical advice.  Judge clarity. Be sure, that a surface of a stone is clean, without any dirt. Firstly, look at a stone with a naked eye. Are there large cracks or inclusions? It is desirabe, that they are not in the center of the stone. Note if inclusions and cracks greatly affect the overall attractiveness of a stone. Then, look at a stone in a 10x gemological loupe for a comprehensive analysis. In this case, pay attention to whether there are large cracks in the stone that go to its surface. The presence of such cracks can sometimes lead to damage of a faceted ruby even from an occasional light impact.“

Weight

Weight of a stone – is a next important factor, that is necessary to keep in mind choosing a ruby. As small stones are more common than large, rarity matters. The larger a ruby is, the higher its price per carat is. Its cost per carat for larger stones rises more significantly in comparison with sapphires and rubies. It is closely related with significant rarity of real large natural samples. Nowadays, it is tricky to find in the market faceted gem-quality ruby over 3 ct. High quality is common just for stones up to 1 ct.

“Practical advice.  Imagine, how stone will be looked in jewelry. For this put a stone «face up» on fingers. Move your palm in different lighting types and note overall attractiveness. Do you like it or not?“

On the video: evaluation of overall attractiveness of heated ruby from Mozambique, weigh 4.06 ct

– In the second part we consider such factors, as cutting, origin, enhancement, varieties of ruby and certificate, that also affect price.

– In the third part we show you real prices per carat.

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