July Birthstone: Rubies

Rubies, the birthstone for July, are one of the most beautiful gemstones, in my opinion. Along with sapphires, emeralds and diamonds, they were once classified as ‘precious’ gemstones, as distinct from semi-precious gemstones such as aquamarines, topazes, garnets and citrines. This classification is no longer taught in gemmology courses. Rather, we look at classifications like crystal gemstones, organic gemstones (eg. pearls) and ornamental gemstones (eg. agates). For the last 125 years or so, gemmologists also study synthetic gemstones, that is, man made gemstones. But, however it is classified rubies are always considered highly desirable gemstones.

Rubies are red gemstones and are part of the corundrum family of gemstones, along with sapphires.  Chromium is the colouring agent for rubies, unlike sapphires which are coloured by iron and titanium.  I will talk a little more below about what makes a ruby a ruby, rather than, say, a pink coloured sapphire.

There are a number of other red stones such as spinels, tourmalines and garnets, and it was not the late 17^th century that gemmologists were able to differentiate a ruby from a spinel. The Black Prince’s ruby, a red stone the size of an egg which is the centre piece of the British Imperial State Crown, is a spinel, as is the large red stone in the Timur ruby necklace, in the British Royal Collection.

Rubies are red but the problem is that red can come in lots of different shades and hues. You just have to think of the colours of red wines, from pinots through to burgundies. Rubies can be dark red or mid range red, and can have overtones of orange, purple and pink. The trouble is that not everyone describes these different reds in the same way. The other issue with colour associated with gems like rubies is when does a ruby stop being a ruby and become instead a purple sapphire or a pink sapphire? There have been attempts to agree on colour standards for gems like rubies, like, for instance, the Munsell Color System which grades colour using hue (colour), value (lightness) and chroma (saturation) (see https://shop.gem-a.com/product/world-of-color/) but it is still a tricky area. The ring above illustrates the difficulties in describing colour. The central gem has strong purple overtones but it is still considered to be a ruby. The Belle Epoque brooch has rubies with a pinky tinge while the rubies in the shamrock ring are a red with few pink or purple overtones.