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Did You Know?

Ruby – from the Latin word ru­ber, which means red – is the most valu­able va­ri­ety of the corun­dum min­eral species, and can com­mand the high­est per-carat price when it comes to coloured stones. Chromium is the trace el­e­ment that makes a ruby red, which ranges from an orange-red to a pur­plish red.

His­tory and Lore

In San­skrit, the ruby is called rat­naraj, or the ‘king of pre­cious stones’. The bright gem can be traced back to the 1st cen­tury AD where the Ro­man scholar Pliny de­scribed the hard­ness and den­sity of ruby in his en­cy­clopaedic work ti­tled ‘Nat­u­ral His­tory’. An­cient Hin­dus be­lieved that those who of­fered fine ru­bies to Lord Kr­ishna were granted re­birth as em­per­ors.

The 4Cs: Clar­ity, Colour, Cut and Carat Weight


Ruby hues range from orange-red to pur­plish red. The finest ruby has a pure, vi­brant red to a slightly pur­plish red hue. As the hue be­comes orange or more pur­plish, the ruby moves down the qual­ity scale into good and com­mer­cial ranges.

Medium to medium-dark tones are pre­ferred as long as the tone isn’t dark enough to have a neg­a­tive ef­fect on bril­liance. At the other ex­treme, if the tone is too light, the stone is con­sid­ered to be a pink sap­phire.


Nearly all ru­bies have in­clu­sions; some in­clu­sions can con­trib­ute pos­i­tively to a ruby’s ap­pear­ance. The pres­ence of ru­tile silk causes light to scat­ter across facets that might oth­er­wise be too dark. This adds soft­ness to the colour and al­lows the colour to spread more evenly across the ruby’s crown.

If large and prom­i­nent in­clu­sions are lo­cated un­der the ta­ble facet, they can greatly di­min­ish the trans­parency, bril­liance and value of the stone. In­clu­sions can also limit a ruby’s dura­bil­ity.


The most com­mon shapes of fash­ioned ru­bies are ovals and cush­ions with bril­liant-cut crowns and step-cut pavil­ions. Round, tril­lion, emerald-cut, pear and mar­quise ru­bies are also avail­able, but these shapes are rare in larger sizes and higher qual­i­ties.

Carat Weight

Fine-qual­ity ru­bies over one carat are rare, but com­mer­cial-qual­ity ru­bies are com­monly avail­able in sizes from 0.15 carat and up.

Spe­cial Notes

Al­most all ru­bies to­day are heat-treated to im­prove colour or clar­ity. These mod­i­fi­ca­tions can dra­mat­i­cally af­fect a ruby’s ap­pear­ance and value. Large, top-qual­ity un­treated ru­bies can com­mand prices much higher than their treated coun­ter­parts be­cause they are rare.

It’s not al­ways pos­si­ble to de­tect heat treat­ment with­out lab test­ing, but you should as­sume that a ruby is heat-treated un­less you see con­clu­sive ev­i­dence that it’s not. An ex­pe­ri­enced gem­mol­o­gist can usu­ally de­tect heat treat­ment by ex­am­in­ing a ruby’s in­clu­sions un­der mag­ni­fi­ca­tion.

While the trade gen­er­ally ac­cepts heat­ing, other ruby treat­ments – in­clud­ing dye­ing with coloured oils or fill­ing sur­face fis­sures with epox­ies or glasses – aren’t as well re­ceived. To­day, lead-glass filled ru­bies are com­monly found in the mar­ket, but they have dura­bil­ity prob­lems and can be dam­aged by many jew­ellery re­pair pro­ce­dures or ex­po­sure to com­mon house­hold chem­i­cals, such as some clean­ing sol­vents. These treat­ments, which of­ten go undis­closed to buy­ers, are not per­ma­nent, and re­quire spe­cial care.

Some corun­dum is also sub­jected to dif­fu­sion treat­ment – adding a colour­ing agent to the heat­ing process – which may sig­nif­i­cantly im­prove a ruby’s colour. This treat­ment is per­ma­nent, but sig­nif­i­cantly af­fects the value of the stone be­cause the colour is not nat­u­ral.

How to Care for Ru­bies

Ruby-stud­ded jew­ellery can be cleaned in an ul­tra­sonic cleaner or steamed, but this should be done by a pro­fes­sional only af­ter a close in­spec­tion to de­ter­mine if any fillers or dyes are present.

As with most gem­stones, a soft moist­ened cloth or a soft bris­tle tooth­brush can be used with mild soap and wa­ter to clean the gem.

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