Sapphires & Ruby
The best Geuda Sapphires (the milky, heatable variety) comes from Sri Lanka. The Thais had a head start of more than 25 years on the heating techniques but the Sri Lankan heat treaters soon caught up with them and in fact have now overtaken them in heating techniques so much so that the better pieces are brought back to Sri Lanka from Thailand for specialized heat treatment.
The heat treatment is permanent and one need not have any fears about the durability of colour even if re-cutting is needed. The greater majority of Blue Sapphires in the market today are heat-treated.
Blue Sapphires are also surface diffusion treated, which process as the name itself implies can loose colour during normal wear if scratches, and other blemishes are to be removed . Re-cutting is out of the question.
Blue Sapphires that have been Beryllium Diffusion treated in order to lighten very dark stones are also in the market and depending on the depth of penetration re-cutting or re-polishing them can be a problem.
Due to these factors more and more customers tend to opt for the unheated gems as an assurance of stability of colour as all the treatment processes involve heating. This has resulted in unheated Blue Sapphires selling at premiums of 40% over the heated variety.
Ruby : This is the red variety of Sapphire ( the term red sapphire is not used) in which colour is caused by Cr as the colouring agent. The intensity of colour depends on the concentration of the trace element.
Rubies are found mainly in Burma, Sri Lanka, Thailand, Cambodia, Vietnam, India (Kashmir), Pakistan, Kenya, Madagascar, Tanzania.
Some Rubies are also heat treated to get rid of the blue tint in the stone which tends to give the Ruby an overall purplish hue which can detract from the value of the gem. This treatment is also permanent.
Many poor quality Rubies from the Mong Shu valley in Burma have their cavities and fissures filled with glass at rather high temperatures to mask these cavities thus giving the Rubies a greater transparency. Of late, Rubies (again poor quality, near opaque) from Kenya, Tanzania and Burma have been treated with lead-glass at low temperatures to fill the cavities. Experienced gemologists will have no difficulty in detecting these filled Rubies.
Pink Sapphire: These are in fact the lighter varieties of Ruby having lower concentrations of Cr as trace elements resulting in lower saturation of color. They are found in all the localities in which rubies are found.
Yellow Sapphires: One comes across the most complex cause of colour in these stones. Primarily the colour is caused by Fe 3+ but yellow sapphires are found in nature with unstable colour due to irradiation from other elements lying in close proximity to these gems in the earth. These may be highly unstable and loose colour once it is exposed to light. On the other hand the radiation in sunlight itself will cause enhancement of colour in certain stones which might then loose this colour when kept in the dark for extended periods of time.
Certain types of milky sapphires (geuda) can be heated to give fine golden yellow coloured gems where the colour is stable. Light yellow sapphires can also be subjected to
x-rays in order to enhance their colour. This treatment is highly unstable and on exposure to strong sunlight tends to loose colour.
Yellow Sapphires are found in Sri Lanka, Madagascar, Burma, Thailand, and Tanzania.
Padparadscha: The gem with the most elusive name. Is the true Padparadscha the colour of the lotus flower which has a strong pink hue and from which it derives its name or is it the exact mix of Pink and orange or then again is it the colour of the tropical sunset? Or to complicate matters is it salmon pink? For sure the sun has not set on this debate between traders. However, most of the Padparadchas preferred by dealers come from Sri Lanka. Padparadschas are also found in Madagascar, Burma, and Vietnam. Certain Pink and Yellowish stones are heat treated to produce Padparadscha`s of the finest colour, This treatment is stable , however Pink Sapphires have of late been Beryllium Diffusion treated to produce an orange coloured “skin” round the stone and this gives the gem a fine Padparadscha colour. This treatment, like most diffusion treatments can cause problems if one tries to polish away the scratches that usually result after long period of wear.
The price of a fine Pad can rival that of the finest Rubies and Sapphires. The highest demand for these stones is from Japan.
White Sapphire: Sapphire (Aluminium Oxide) in its purest form, that is, devoid of any trace elements will be white and a well cut White Sapphire in small sizes can fool even a trained eye to mistake it for a diamond. White Sapphires are found in almost all localities where other varieties of Sapphires are found. Certain light blue sapphires and yellow sapphires can be heat treated to remove any lingering colour resulting in brilliant White Sapphires.
Green Sapphires: The cause of colour is probably a combination of those giving blue and yellow sapphires. A real leaf green sapphire is quite rare. Most of them are a less desirable yellowish green. However, jewellers have made good use of these green sapphires by putting out jewellery mounted with subtly varying colours of gems which are quite attractive.
Blue Star Sapphire: The cause of colour is the same as in Blue Sapphires.The star or asterism is effected by the reflection of light from 3 layers of fine, densely packed rutile needles oriented in definite directions which cut each other at 120 degree angles giving a six-rayed star. Gems showing such effects are referred to as “phenomenal stones”. The quality of a star depends on body colour, a silvery star on a blue background being the most desirable. The milky white or grey-white stone with a white star ends up at the bottom of the list. The strength of the star and also how true the ray runs is a factor effecting quality. Wavering rays and broken rays tend to depress the quality just as much as incomplete rays – the ray should run from the dome all the way to the girdle. Needless to say transparent stones fetch higher prices.
Star Sapphires have a limited market and this is mainly in the USA and Japan. This may be one of the reasons for the lower prices commanded by them and since of late this has resulted in the lighter blue star sapphires having their rutile needles ( geuda effect) heat treated thereby destroying their asterism and changing these stones into ordinary blue sapphires which fetch much higher prices. This has caused a considerable shortage of medium quality star sapphires in the market.
Star Rubies: The cause of asterism is the same as in Blue Sapphires and the most desirable stones are those with an intense red with a silvery star. The criteria for quality that apply to star sapphires play a role here too. Just as in the facetted rubies cavities in star rubies too are sometimes filled with glass to improve transparency. Japan and USA are virtually the markets for these stones. For the same reasons as in the case of star rubies medium quality star rubies are becoming hard to find. /div>