Corundum of a red colour are identified as rubies. Being corundum these have all the optical, physical and chemical properties of the mineral. These also have negligible quantities of chromic oxide in their compositions which do not in any way affect the general chemical formula. It is this element, chromic oxide which is responsible for the red colour of ruby. The colour in rubies could be in various shades and tones and is dependent on the quantity of chromic oxide present, its ratio in relation to other elements in the composition, and the nature of its distribution. The depth and intensity of color is related to these factors while the distribution of colour in ruby could be patchy, banded or uniform. The presence of chromic oxide in the correct proportions, in the desired quantities, in the correct manner of distribution within a glassy textured transparent body, free from flaws and inclusions produced the ruby of optimum quality. Such stones are most beautiful and are highly prized. In Sri Lanka the occurrence of rubies are comparatively rare in comparison to blue sapphires although adequate supplies are available to cater to the market. Superlative quality rubies from Miyanmar (Buruma) hace earned universal acclaim as the best in comparison to rubies from other regions of the world. This statement does not in any way express the idea that there is no exception to the rule. Other localities have occasionally shown up rubies of exceptional beauty that compare well with or even surpass the beauty of their Myanmar counterparts. Sri Lanka has proved this point although such occurrences have been rare. Such stones have always been from the Uda – Walawe region, which can be considered as the locality for rubies that compare most favorably with the best from Miyanmar.
Determining the possible locality of a ruby by colour and appearance alone would certainly lead to confusion and controversy. To eliminate such controversy other factors like mineral inclusions and twinning planes are of importance and should be taken into consideration. Rubies are generally sensitive to light purely because the sensitivity of the colouring element, chromium; and their luster appearance could differ according to the nature of the light under which they are observed. It is best that rubies are observed under natural daylight conditions, always remembering the fact that daylight conditions are different in different parts of the world; which factor could consequently creat a different colour sensation on the human eye.
The colour in rubies could vary from pale to a deep and intense red; the colours ranging from pale rose red to a deep red. Most Sri Lankan varieties are of a pinkish red and display a tinge of purple which factor perhaps is sufficient to betray to the experienced person that the stones are of Sri Lankan origin. These purplish tints are attributed to the presence of iron in addition to chromic oxide in the composition. Such stones when subject to intense heat would either lose or diminish the purplish tint thereby highlighting the principle colour, red. In his book “precious Stones”, Bauer (1971) states that “ the shade of colour most admired is the deep pure carmine red with a slightly bluish tine.” It is not uncommon to notice this faint bluish tinge in this category of rubies. This colour is referred to as ‘pigeon blood red’ in gem circles. Furthermore, the colour distribution in rubies is invariably either patchy or banded with colour bands alternating with the colourless. The patchy colour distribution in the ruby could be remedied by subjecting such stones to intense heat. It has been noted that the colour in such stones when gradually heated gets distributed as a final outcome. Flawless rubies of a deep intense red with uniform distribution of colour and with a pleasing tone are extremely rare and consequently very valuable.
A currently prevailing controversial question is ; where lies the demarcation line between the ruby as defined and the pink sapphire? Difference of opinion is rife. But sooner or later this issue has to be resolved. In this publication it is not intended to discuss this subject in detail. Nevertheless it is necessary to highlight a few vital and important opinions as put together by Widess (1981) in ‘Jewelers Circular Keystones: February 1981 ‘which are as follows;
The gemological Institute of America, “Only transparent corundum of medium light to dark tones of red to purple hues is properly called ruby. Very light tones of red are correctly called pink sapphires. Even some stones that are light rather than very light in tone are properly called pink sapphires. A very intense red colour is necessary to justifiy the use of thee term ruby’.
Peter T. Sciambra, Director, International Gemological Institute, “I.G.I.’ s definition is basically the same as that of the G. I. A. except that it leaves out the phrase ‘ a very intense red’ colour is necessary.”
Charles I. Carmona, Vice President, and Guild Laboratories “The guidelines for a ruby are very similar to G. I. A. except we add brownish red”.
Thomas E. Tashy Jr. (G. G.: F. G. A.) Director, Independent Gemological Laboratory says “We mostly adhere to the G. I. A. guidelines. We differ in very light stones which we call pink rubies instead of pink sapphires.”
David Widess (G. G.) of Widess & Sons, Los Angeles says “Any corundum of reddish hue no matter what lightness or intensity, tint, shade or tone shold be called a ruby.”
Dr Earl Anderson ph.D, President of the Gemological Research Group Inc. says that he is in “perfect agreement with and shares the opinion of David Widess” and goes on to say that any corundum of reddish hue no matter what lightness of intensity, tint, shade or tone should be called a ruby.”
Herbert Smith (1930) in his publication “Gemstones” states that “the tint of red stones (rubies) varies considerably in depth. Jewellers term them pink sapphires when pale but of course no sharp distinction can be drawn between them and rubies.’ Richard Hughes of the Asian Institute of Gemological Sciences after making reference to historical background explicitly states “In light of the strong historical evidence suggesting that the term ruby was originally understood to include all red to slightly bluish red corundum from the very lightest to deepest tones, A.I.G.S. is abandoning the use of pink sapphire as an individual variety of corundum. As of this moment we will no longer use the term, either in our educational programmes or on the gem identification reports issued by our laboratory.”
From all this the reader will realize the nature of the controversy. Even at present we are still grappling with this issue and what should be stated is, that this is not so much a scientific or a gemological problem. After all, this nomenclature is based on colour alone an as such the verdict is with the gem trading circles. There is reason to believe that Sri Lanka is the original source of the variety identified as pink sapphires.
As a rule, ruby deposits as such have not been specifically localized in Sri Lanka and are found in association with other members of the corundum family. However, as indicated earlier the stones of better quality have been more often than not found within
the Embilipitiya- Uda- Walawe environs.