Ruby Gemstones: Colour, Quality, Treatments and Care
A ruby can be a vivid red centre stone, a softly glowing cabochon or a small accent in a piece of jewellery. The name carries plenty of romance, but the details behind a particular stone matter more than broad claims about rarity or value. Colour, clarity, cut, treatments and documentation all shape what you see.
Ruby is the red variety of corundum, the same mineral family as sapphire. Chromium gives it its red colour. Natural and laboratory-grown rubies can look alike, so appearance alone cannot confirm how a stone formed. This guide explains what to look for and what useful questions to ask.
Ruby in brief
Corundum ranks 9 on the Mohs hardness scale, which helps explain why ruby is used in jewellery made for regular wear. Hardness describes resistance to scratching; it does not make every ruby immune to impact or treatment-related damage. A stone’s condition and any filling or colour treatment should be part of its care story.
What gives ruby its red colour?
Chromium in corundum produces ruby’s red, which can range from orangey red to purplish red. The amount of chromium, the stone’s other trace elements and the way light moves through the material all affect the colour you see. Some rubies also fluoresce red, adding to their appearance in certain lighting.
There is no single shade that everyone must prefer. In gem trade and laboratory descriptions, the boundary between ruby and pink sapphire can depend on how dominant red appears and on the classification convention being used. Terms such as “pigeon’s blood” are evocative trade descriptions, not a promise that every stone from one locality has the same colour or quality. GIA explains these distinctions in its ruby quality guide.
When comparing stones, look at them in consistent neutral light if possible. Notice whether the colour looks even face-up, whether dark areas hide the red, and whether the hue still appeals to you away from dramatic shop lighting. A photograph or screen can shift colour, so use it as a starting point rather than a substitute for inspection.
Ruby and sapphire share a mineral family
Ruby and sapphire are both corundum. Ruby describes red corundum; other colours are generally called sapphire. Their shared chemistry makes the comparison useful: colour is central to the name, while clarity, cut, size and treatments help describe the individual stone. Read our sapphire guide for a closer look at the other familiar corundum variety.
Corundum crystals form in different geological settings. Chromium is responsible for ruby’s red, while other trace elements can create different colours in corundum. A source name can add geological context, but a mine or country name on its own does not tell you whether a particular ruby is attractive, durable or responsibly traceable.
Rough crystals are shaped to make the most of their colour and material. Oval and cushion cuts are common, but the best outline depends on the rough, the cutter’s choices and the look the wearer wants. A cabochon has a smooth curved top and can show a star effect when suitable aligned inclusions are present.
How to compare ruby quality
Colour is often the first thing people notice, but it is only one part of the picture. Compare the stone face-up: does its red look lively, or do dark areas make it seem flat? Is the colour reasonably even for the style of stone? Personal preference matters, and two rubies with different appearances can both be beautiful.
Clarity is about inclusions and how they affect the stone. Natural rubies commonly contain internal features; a completely inclusion-free appearance is not a sensible requirement. Fine needle-like inclusions, sometimes called silk, may be visible under magnification. Large or surface-reaching features can affect transparency, appearance or durability, so ask for a clear explanation rather than relying on a single close-up photograph.
Cut describes how the rough was fashioned. Check whether the stone looks balanced from the top, whether the facets return light pleasingly and whether a see-through “window” is visible in the centre. Carat is weight, not a direct measure of face-up size: proportions and cut can make two stones of the same weight look different. GIA’s coloured-stone reports describe characteristics; they do not assign ruby a universal quality grade.
Treatments and reports: what to ask
Many rubies are heat-treated to improve their appearance. Other processes can include diffusion or filling surface-reaching fractures with glass. Treatments affect how a stone should be described, compared and cared for. Ask the seller to state known treatments in writing, and be wary of descriptions that simply say “untreated” without supporting information.
A report from an independent gem laboratory can help distinguish natural from laboratory-grown material and identify detectable treatments. GIA’s ruby report FAQ explains that its Colored Stone Identification & Origin Report records characteristics and detectable treatment, and may give an origin opinion when requested and possible; it does not grade ruby. Check that the report number and stone details match the item being offered.
Laboratory-grown ruby is real corundum grown by people rather than formed naturally in the ground. It is a different origin category, not a fake stone. Simulants are different materials that imitate ruby. A careful listing should name which kind of material is being sold and describe treatments clearly.
Buying with clear information
Before choosing a ruby, ask whether it is natural, laboratory-grown or a simulant; what treatments are known; and whether a report is available. Compare measurements as well as carat weight, check the return terms, and ask whether the seller can explain any origin claim. A report supports identification, but it does not by itself prove a complete supply-chain history or guarantee a price.
Ruby prices vary widely with quality, treatment, size, documentation and market conditions, so a fixed price-per-carat range can mislead. Treat claims about investment or guaranteed appreciation with caution. If ethical sourcing matters to you, ask what evidence supports the seller’s traceability statement and how far that evidence reaches. If the answer is unclear, regard the source as unknown instead of filling the gap with an assumption.
For another perspective on coloured gems, see our guides to emeralds and garnets. These stones belong to different mineral groups and offer their own colour and care considerations.
Ruby care and cleaning
Corundum is hard and tough, but a stone’s treatment and setting still matter. GIA says warm, soapy water is a safe cleaning method for ruby. The safest routine for a ruby whose treatment is unknown is gentle hand-cleaning and a soft cloth; avoid steam or ultrasonic cleaning until a jeweller has confirmed that the stone and setting are suitable.
Use lukewarm water, a little mild soap and a soft brush, then rinse carefully and dry with a lint-free cloth. If the ruby is fracture-filled, cavity-filled or dyed, GIA recommends cleaning it only with a damp cloth because those treatments can be damaged by mild chemicals. See the full ruby care and cleaning guide and ask a qualified jeweller before using a cleaning machine.
Ruby questions, answered
Is every ruby naturally red?
Ruby’s colour is red because of chromium in corundum, but the hue varies. Trade and laboratory conventions can differ around the line between ruby and pink sapphire.
Does a GIA report give a ruby a grade?
No. GIA identifies and describes a ruby, including detectable treatments, but does not give it a universal quality grade.
Can I clean any ruby in an ultrasonic machine?
No. Treatment and setting matter. Use gentle soapy water as a safe starting point, and choose a damp cloth for fracture-filled, cavity-filled or dyed stones.
A ruby is easiest to appreciate when its colour, treatments and documentation are described plainly. Take time to compare the actual stone, ask specific questions and choose the one whose appearance and story feel right to you.