When it comes to grading gems, rubies are a bit of a special case.
The reason for this is because rubies can only come in different hues of red, otherwise it will be classified as a sapphire since it is the same gemstone.
So how do gemologists decide what the quality of a ruby is?
If you’re familiar with how diamonds are graded, the process for grading rubies is very similar with some additions. There are four main criteria that are used: color, clarity, cut, and carat weight.
There are a few more however, which we will discuss further.
In this blog post, we will explore the four Cs of ruby quality so that you can better understand what to look for when buying a ruby.
Table of Contents
What Are The Four Cs of Ruby Grading?
When you think of diamonds, you might think of the classic four Cs: color, clarity, cut, and carat weight.
However, these are not the only criteria used to grade rubies. In fact, the 4 Cs are just the start, and the value of a ruby will include any “enhancements” that have been made to the stone, such as heat treatment.
How Color is Graded in Rubies
One of the things about colored gemstones is the fact that the color is determined by the region of a country that the stones are mined from.
You have no doubt heard of “Burmese Ruby”?
Well, that region of the world seems to mine a red color saturation that is considered the most desirable.
Someone, somewhere in the world set a standard of what the shade of red a ruby should be in order to be considered as ideal.
So when you see a price being applied to a ruby, and if that price is astronomical, then chances are that the ruby had the “approved” shade of desirable red that is the most sought after by elites.
Ruby comes from the Latin word “ruber” which, as you all know, means red. So to determine the quality of a ruby, part of that is based on color, hue, saturation and tone.
| Color Grade | Description |
|---|---|
| Tone | The tone of a ruby refers to how much color is in it. It ranges from very dark, to very light, with medium tone being ideal. A ruby that is rated high will have a tone that is neither too light nor too dark. |
| Hue | Basic hues include a range of red to orange, to purple and everything in between. If a ruby has a red hue, it is considered to be ideal rather than if it is showing a slight hue of purple or orange. |
| Saturation | Saturation gives a ruby its color and intensity. The saturation categories include vivid, strong, fair, medium and weak. This simply means that the ruby ranges from pale red to a red that is vivid and intense. The higher the vivid saturation of a ruby, the more valuable it is. |
How Clarity is Graded in Rubies
Rubies are very much like diamonds when it comes to grading for clarity, except that there are some types of inclusions that you would not find in diamonds that are naturally found in rubies.
The top grade for clarity in ruby is VVS, which is very very slightly included. These are minor and can only be seen under 10x magnification.
They have no effect on the appearance of the ruby.
Notice that the highest grade does not start with Flawless. That is because there will always be something found in a ruby given the way they are grown in nature as opposed to diamonds.
The grading scale goes all the way down to I3 which is a grade that means that there are so many inclusions that it interferes with brilliance, transparency and appearance.
Of course, you would hope to have a ruby with the higher grades such as the more affordable SI1 or SI2.
The types of inclusions found in rubies are:
| Inclusion Type | Description |
|---|---|
| Crystals | Solid inclusions ranging in shape and size. |
| Needles | Long and thin inclusions that are crystals filled with gas or liquid. |
| Silk | Very fine fibers of minerals that resemble silk. This is the “preferred” type where rubies are concerned. |
| Cracks | Feather-like inclusions that are also called fractures or fissures. |
| Twinning | Two crystals that have grown out of one another or next to each other. |
| Parting | Breaks that occur along a plane of weakness. |
| Halos | Circular features that surround a crystal. |
All or most of these inclusions aforementioned are to be expected to be found inside rubies.
They “tell” that the stone is natural rather than synthetic.
To the degree that there are inclusions present that interfere with the clarity or transparency of the stone is how a ruby will be graded.
How Cut is Graded in Rubies
The cut of an ideal ruby will have a depth and width ratio higher than diamond cuts will have. A good quality of ruby will have a depth percentage of 65% to 80%.
Stones that are very deep will look smaller than expected for their weight, but they will also be able to show off more color than they would if they had been cut to normal proportions.
The deep cut stones preserve weight which of course, not only make the color deeper, but this will increase the cost. Stones that are cut shallow will look big for their weight, but they will appear lighter in color than the deeper cut stones will.
Keep in mind that symmetry is also a feature within the cut that enables light to be reflective evenly.
The different types of cuts are:
[Table]
How Carat Weight is Graded in Rubies
The term “bigger is better” is true when it comes to gemstones, but only up to a certain point.
Although bigger stones are consistently more valuable than smaller ones, if all the other factors are at play such as the best color, exceptional clarity and fantastic cut, then a smaller stone could cost you more than a larger one of lesser grade.
The same holds true for all colored gemstones including diamonds. A half carat flawless diamond is going to cost far more than a 2 carat diamond that is graded of I1 or worse. Rubies are no exception.
Treatments That Affect Ruby Grading
There have been some changes since the 1960’s to our colored gemstones. They have been “treated” to enhance their color and clarity to such a point that the market has been flooded with them.
Ninety-five percent of colored gemstones have been treated in some way in order to make their appearance look better, but these treatments will reduce the overall value of the stones. Here are two treatments that you will find mentioned in a Gemologist report:
Heat Treatment
Heating a gemstone of any type is now a common trade practice. Gone are the days wherein gemstones are “as is.”
Gone with that is also their value, to be frank.
Heating is cheating.
The color is made much deeper, and the heat applied can also include another treatment of injecting a glass like substance that will fill in fissures and cracks to make the stone more stable.
While this seems like a good idea if the idea is just to have a pretty stone, the price point for heated stones should reflect that the stone has had some help.
If you want a “virgin” gemstone, be prepared to pay 5 times the price than you would for a heated one unless it is a tanzanite.
Tanzanites get their deep purple blue color from being heated and this is what people actually want to see when they are looking to buy one. Non heated Tanzanites look more like aquamarines and some even have a brownish hue.
Rubies that have been heated do look deeper red, but upon a more in depth look, the internal structure is speaking of being wounded.
Glass Filling
While a heat treated stone is still the stone it was originally, with the exception of being subjected to extremely high heat to make the color better, glass filled stones totally change the nature of the stone forever.
It was not that long ago that a new form of treatment known as “lead glass filling” came on the market.
This treatment takes non-gem quality rubies and fills cavities and fractures in them with lead glass, which alters the construction of the stone.
These rubies had no trade use and were not accepted by jewelry stores or manufactures.
The problem is that although glass treatment is still not accepted as a trade practice, stores found that customers did not know or ask about the practice and chose their rubies by appearance and size only.
Lead glass can make up a substantial portion of the stone until it is no longer considered a ruby, and is left unstable which will deteriorate over time.
Any time you buy a ruby, the seller must disclose if the treatment was heat or glass filling.
Goldsmiths generally do not want to work on jewelry that has gemstones which have been filled because the heat from soldering could cause the stone to explode.
What To Look For When Buying A Ruby
When you consider buying a ruby, look first to find out if any treatment is present. Usually, heat treatment is what you will have to settle for unless you are prepared to pay a high price.
- Once the ruby is determined to not be glass filled, then move on to hue so you can choose the color you prefer.
- Look to see how transparent the ruby is. You do not want a ruby that is opaque or difficult for light to be seen through it. Transparent rubies have excellent brilliance regardless of the inclusions that they may have.
- After that, look at the size and shape of the ruby. Oval, cushion, or round are all excellent choices for a ruby.
- And lastly, look at the carat weight of the stone to be sure that it meets your needs. If the price is too good to be true, then it probably is.
What is the best grade of ruby?
It is said that the best grade of ruby is the Burmese pigeon blood red ruby. Rubies are mined all over the world, but the Burmese ruby seems to have the hue that most people prefer. When hue meets excellent clarity and transparency, you will have the highest grade of ruby provided it has not been treated.
How can you tell a quality ruby?
In order to tell if you have found a quality ruby, the best thing to do is find out if there is a Certified Gemologist report that has been done to grade the stone.
If there is not, and if you are considering buying from a jewelry store, ask them to send it out for grading (at their expense) to a GIA laboratory before you consider buying.
You may not be able to tell if what appears to be a quality ruby is lab grown otherwise and therefore will not want to pay a price unless you know what is the full story on the ruby.
A jewelry store worth their salt will know what they have and will disclose it to you before you purchase.
How much is a 1 carat ruby worth?
A one carat ruby can be worth approximately $11,000 if the hue and clarity is very good. This supposes that it has not received any indications of treatments of any kind. A one carat ruby is more valuable than a diamond of similar grade. However, diamonds do not have the same scrutiny when it comes to undergoing treatments.
What is the best clarity for a ruby?
The best clarity for a ruby is eye clean, meaning that inclusions are not visible to the naked eye. Most people prefer a ruby with a VS (Very Slightly included) or SI (Slightly Included) rating on the GIA Gemological Report.
Keep in mind that even if a ruby has been treated, it can still be beautiful and have excellent clarity. The important thing is that you are aware of the treatments and that you are comfortable with them.
Final Thoughts
There are few gemstones more beautiful than a ruby.
Rubies come in various shades and hues of reds. But as a matter of fact, pink sapphires are rubies that never made the color debut into the red zone.
Pink sapphires are devastatingly beautiful also, but do not get to be called rubies. This however, opened up a market for the pink “off” color and they are doing well nevertheless.
When you purchase a ruby, be sure that you understand what treatments it may have received so that you do not inadvertently damage the stone.