Gemstones
Gemstone Color
Color decides most of what a colored stone is worth. Split it into hue, tone and saturation and you can compare two stones deliberately instead of by impression.
Diamonds and colored stones are graded on opposite principles. In a white diamond, the absence of color is what you pay for. In a sapphire, ruby, or emerald, the presence and quality of color is almost the entire value.
“Nice blue” is not enough to shop with. The trade breaks color into three components, and once you can name them you can say precisely why you prefer one stone over another, and whether the premium on it is justified.
Component 1
Hue, which color it is
Hue is the basic color: red, blue, green, yellow, purple, orange. Very few gemstones are a single pure hue. Most carry a secondary hue alongside the primary one, which is why stones are described as “violetish blue” or “bluish green” rather than just blue or green.
- A pure primary hue is rarer and generally more valuable than a mixed one.
- Not every secondary hue is a penalty. A touch of violet in a blue sapphire is welcome; a touch of green is not. A hint of blue in a ruby is prized; orange is not.
- The naming convention puts the secondary first: violetish blue is a blue stone with a violet cast, not the reverse.
Component 2
Tone, how light or dark it is
Tone runs from colorless to black, conventionally scored 0 to 10. It is the easiest of the three to judge by eye and the one most often got wrong when buying from photographs, which routinely brighten dark stones.
| Tone | Description | How it reads |
|---|---|---|
| 0–2 | Colorless to very light | Pale and washed out; little presence on the hand |
| 3–4 | Light to medium-light | Bright and lively, but short of rich |
| 5–6 | Medium | Usually the sweet spot, full color, still lively |
| 7–8 | Medium-dark | Rich and deep; the top of the range for most stones |
| 9–10 | Very dark to black | Goes flat and lifeless outside bright light |
Medium to medium-dark is where most gemstones look their best and where prices peak. Below that a stone lacks presence; above it, it closes up in ordinary indoor light, which is where you will actually be wearing it.
Component 3
Saturation, how pure and intense it is
Saturation measures how much grey or brown mutes the hue. It is the component most closely tied to price, and the hardest to see until you have two stones side by side, at which point it becomes obvious.
- Greyish or brownish: the hue is noticeably dulled. Lowest value.
- Slightly greyish or brownish: a faint mute over the color.
- Moderately strong to strong, clean, attractive color; where most good commercial stones sit.
- Vivid, no grey or brown at all. This is what “vivid” on a laboratory report means, and it carries a steep premium.
The ideal color, stone by stone
Sapphire
Medium to medium-dark, vividly saturated blue that holds its color in low light. Violet secondary is fine; green secondary lowers value.
Read the guideRuby
Pure vivid red, medium to medium-dark, with a faint blue undertone: the pigeon's blood benchmark. Orange or brown casts cost value.
Read the guideEmerald
Pure vivid green, medium to medium-dark, free of brown or grey. Slight blue is welcome; yellow secondary is less prized.
Read the guideOther stones
Aquamarine is valued for pure blue without green; amethyst for deep purple with red flashes; tanzanite for rich blue-violet at vivid saturation.
Three things that change the color you see
Lighting
Daylight shows the truest color; incandescent light warms reds and can flatter a mediocre ruby; fluorescent light cools blues. Alexandrite goes further and changes hue outright between light sources. Always view a stone in more than one light before committing.
Treatment
Heat is the most common enhancement, is permanent, and is accepted throughout the trade. Diffusion, irradiation, dyeing, and fracture filling are different matters. They can be shallow, unstable, or vulnerable to ordinary repair work. Reputable sellers disclose all of it, and should provide an independent report on request.
Cut
Proportions decide how much light returns through the stone. Cut too shallow and you get a “window”: a pale patch you can see straight through. Cut too deep and the stone darkens at the center. Either fault makes good color look worse than it is.
How to judge a stone yourself
- Compare, don’t contemplate. A single stone always looks good. Put two or three side by side and the differences in saturation appear immediately.
- Move it into different light. Daylight by a window, then indoors. A stone that only works under a jeweler’s spotlight will disappoint at home.
- Tilt it. Look for windowing, extinction (dark patches), and color zoning from several angles.
- Ask what has been done to it. Get treatment disclosure in writing, and a laboratory report for anything significant.
- Consider the setting. Yellow gold warms a stone’s color; white metals stay neutral and keep cool hues crisp.
- Then trust your eye. Grading language exists to explain a preference, not to overrule it. The best color is the one you want to look at for the next thirty years.
Ready to look at stones?
Browse our color stone rings, or talk to a consultant about sourcing a particular color, size, and certification.