Ruby and Sapphire Survey: Where Do You Draw the Line?


Summary
The distinction between ruby and sapphire is more nebulous than most people realize. These gems are the same mineral: corundum. Color is the only thing that separates them.

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.

Reading time: 7 min 31 sec
ruby & sapphire survey - mozambique ruby ring
Though most would call the center stone in this ring a ruby, some may argue that it’s too pink to be “ruby.” © CustomMade. Used with permission.

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 certify a pastel 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.

ruby and sapphire survey - circle ruby color

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.

ruby and sapphire survey - ruby word cloud

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.

ruby and sapphire survey - circle pink sapphire color

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.

ruby and sapphire survey - pink sapphire word cloud

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.

ruby and sapphire survey - circle padparadscha color

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 certify a sapphire as padparadscha if it shows significant color zoning.

ruby and sapphire survey - padparadscha sapphire word cloud

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.

ruby and sapphire survey - ruby example image
There’s more than one color in this image, just like a real-life ruby. Ruby oval, 0.99 cts. Photo by Wiener Edelstein Zentrum. Licensed under CC By-SA 3.0.

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 certify a stone as “padparadscha” only if there’s no evidence of treatment, untreated stones with the same color may not be certified as “padparadscha.” This creates a difference in price past the difference in rarity.

About the author
Addison Rice
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.
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