Sapphire Specialist Mini Course
Ruby and Sapphire Survey: Where Do You Draw the Line?
We wanted to learn more about the fuzzy line between ruby, pink sapphire, and padparadscha sapphire. So, in September 2018, we sent out a survey asking for people's opinions on these gems.
Our 281 respondents had varying and often overlapping opinions about color in our ruby and sapphire survey. Read on to learn more about the survey results and the distinction between these gems.
Purchase Sapphire Specialist Mini CourseBeloved for its celestial blues and violets and exceptional hardness and durability, the sapphire is a long standing favored gemstone. Take an in-depth look at sapphires, from how they form to how to appraise them. Looking to buy or sell a sapphire? Learn how to determine sapphire quality. Every sapphire lover will learn something new in this course.
Ruby and Sapphire Survey: Color
Ruby is red corundum, while sapphire is any other color. Long ago, pink corundum was also considered to be ruby, since pink is a lighter tone of red. More recently, Western gemologists have distinguished red and pink.
While gemological laboratories have standards distinguishing ruby from pink sapphire, these aren't universal. Some laboratories may call a borderline stone a ruby, while others may call it a pink sapphire.
Our survey also addressed another variety: padparadscha sapphire. These gems are traditionally described as lotus or sunset-colored. Unlike most gem varieties, padparadscha is best known for its pastel hues. In fact, Western gemologists assert that padparadschas must be pastel. Many gemological laboratories will designate a pastel sapphire as padparadscha but not a more vibrantly colored one.
Top Color Choices
When we asked people to select the top color for each of these three gems, the results were widespread. To visualize it, we plotted the colors in 3D HSL-space (hue, saturation, and lightness or tone). Larger markers indicate that more people chose that color.
In these selected views from the plot, you can see the overview and hue vs tone for all three gems, combined as well as individually. From the tone vs saturation plots, you can see that some choices for ruby had low saturation. In the last slide, you can clearly see the overlap of pink sapphire and padparadscha sapphire.
You can view and interact with the embedded 3D HSL-space below. (The embedded plot will only appear on desktops).
For top ruby color, respondents chose colors very close to true red in hue. In part, this is because the color palette provided started and ended in red, rather than being centered on red. This made it easier to select a pure red hue.
Top colors chosen for pink sapphires tended toward purple, and the colors for padparadscha tended toward orange.
Notably, many of the colors overlap. What some chose as a top color for pink sapphire, others saw as a top color for padparadscha or even ruby.
Ruby Color: Pigeon's Blood to Red Raspberry
When asked to circle the area for ruby color, most respondents stuck to the middle and upper-right halves of the color gradient — from a pure red to strongly purplish red. However, some circles encompassed the entire space or significant portions of the orange and lighter pink areas.
In the comments, many respondents mentioned pigeon's blood, vivid saturation, and a preference for deep, rich reds. Many also noted a preference for purplish reds or even raspberry colors, while a few preferred a slightly orange red. Others noted a preference for Burma rubies over Thai rubies.
While the most highly prized rubies are "pigeon's blood red," any corundum with a primary red hue, high enough saturation, and dark enough tone is ruby.
Pink Sapphire: Bubble Gum, Baby Pink, and Hot Pink
When asked to circle pink sapphire color, respondents primarily chose lighter tones tending toward purple, though a few also included hues on the orange side of the spectrum.
In the comments, there was no clear consensus on a preference for pink sapphire color. Some described an ideal gem as "hot pink," "deep pink," "vivid," and "electric." Others said a pink sapphire should be "baby pink" or "pastel." Still others said it should be "true pink," though this could mean anything.
The most highly priced pink sapphires are just over the line from ruby. Although hot pink and raspberry hues that straddle the line command higher prices, some may prefer the lighter pastels.
Padparadscha Sapphire: Lotus, Sunset, and Fruit Salad
Given its subjective description, respondents chose a wide range of hues for padparadscha. Though most stayed in the pastel and orange side of the color space, some chose more deeply saturated colors.
Padparadscha sapphires stray further from the pure hues, so respondents were more creative in their comments. In addition to traditional "lotus" and "sunset" descriptions, "peach," "melon," "apricot," and "salmon" were used to describe the color.
Some noted that a padparadscha should have "deep flashes" of pink within an orange body or opined that it should show multiple colors. However, gem laboratories that assign the padparadscha descriptor won't designate a sapphire as padparadscha if it shows significant color zoning.
Indeed, padparadscha is one of the most debated gem varieties. Its description is often subjective, and some commenters noted how it's difficult to define until you actually see the gem.
Wait… These Colors Don't Look Like my Ring!
One respondent noted that the ruby ring on their finger isn't the same color as anything on their screen. Most likely, this isn't quite true. However, this comment reveals a special difficulty in creating a survey on color.
When we look at a gem, we see many different colors, its transparency, and the way the light hits it. Comparing this to a flat color is difficult. Think about it — if you were to paint a ruby, what color would you use?
It's certainly possible to depict a fine ruby using flat colors. However, without training in color, pinpointing the colors you're looking for is hard.
By pixelating the image above and analyzing its colors, we can find the twelve most common colors and the average color of the ruby.
The average color of this ruby is a purplish red with 73% tone. Unlike most of the choices for top color, this color is not 100% saturated. However, some of the colors in the image have full saturation.
Reducing a gem's color to a single, flat color isn't an accurate way to depict its color, but without this simplification, it's far more difficult to conduct a survey on color.
Ruby and Sapphire Survey: Price
When we asked for the price of an unheated 1-ct top-color ruby, we weren't expecting such a wide range of responses. Some said $5, and others $1,000,000! It's possible that the lowest numbers were meant to be interpreted as thousands. However, there's no way to tell.
Because of the wide range of values, the arithmetic mean (average) isn't very useful. Instead, we'll discuss the geometric mean, which is less heavily impacted by outliers.
Geometric means for untreated ruby, pink sapphire, and padparadscha sapphire are $926, $549, and $951, respectively. These prices are all quite low for top-color corundum. They also reveal an interesting trend — padparadscha sapphires were valued higher than rubies.
Since some of the lower values may have been misinterpreted, we can look at each respondent's ratios of ruby to pink sapphire pricing and ruby to padparadscha sapphire pricing. A top-color ruby should go for about 5-10 times the price of a pink sapphire and about 3-5 times a padparadscha. Only 12 people responded with relative values in this range. Most respondents gave prices for these gems closer to each other.
However, 33 people gave prices for pink sapphire above the price for ruby, and 83 gave higher prices for padparadscha sapphire than ruby. While some people may prefer pink and sunset colors to pure reds, a top-color ruby would certainly command higher prices than a pink sapphire or padparadscha sapphire.
Treated and Untreated Prices
How heat treatments impact pricing is poorly understood within the gem trade as well as the broader population.
For most gems, untreated material commands a premium of about 30%. Untreated fine blue sapphires have prices about 50% higher than treated material. For a top-color ruby, however, gem treatment can impact price more heavily. Depending on size, untreated material may be 2-5 times more expensive than heat-treated material.
Across all three gem varieties, about half of respondents priced untreated material 2-5 times higher. Most other responses gave a more modest price bump for untreated material, around 20-50%.
So, about half of respondents gave a relative price appropriate for ruby, and the other half gave a relative price appropriate for other gems.
For padparadscha sapphires, the story is more complicated. Since certain gem labs will designate a stone as "padparadscha" only if there's no evidence of treatment, untreated stones with the same color may not be designated as "padparadscha." This creates a difference in price past the difference in rarity.
A geologist, environmental engineer and Caltech graduate, Addison’s interest in the mesmerizing and beautiful results of earth’s geological processes began in her elementary school’s environmental club. When she isn’t writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.
Never Stop Learning
When you join the IGS community, you get trusted diamond & gemstone information when you need it.
Get Gemology Insights
Get started with the International Gem Society’s free guide to gemstone identification. Join our weekly newsletter & get a free copy of the Gem ID Checklist!