colour too relaxes muscles, relieves tension and has an overall soothing
effect, so much so that jewellers suggest that pink gemstones shoul be worn
at any important event.
While a gemstone can change the personality and health of one who wears it,
any individual can in turn change the character of the gem over time. Sweat
and body oils give turquoise a green tinge and darken it. On the other hand,
emeralds may absorb oil and get more lustrous. Rubbing against the body,
pearls may gradually lose their shine and opals, their fire. Some stones
like amber develop an electric charge when rubbed while hematite acquires
magnetic properties. Whatever effects a gem may have because of its colour,
three factors determine the value of a coloured stone. The hue defines
whether it is red, blue or green. The next factor is the purity of the
colour or the absence of a mixture o hues. Finally, the intensity of colour
is another criterion. The value of a stone depends on these three
parameters, the best tone being the most expensive. For instance, a good
ruby should shine bright and pure red, without a trace of blue, while a blue
sapphire must be a deep blue without a trace of yellow or black. The most
expensive diamond would have no colour at all, or else should have a deep
colour, the richest and purest in nature.
The perception of colour also depends very much on the light that falls on
the object. A white sheet appear red when viewed in red light. Textiles too
appear to change colour with the ambient light and customers always look at
fabric in sunlight outside the store when different pieces have to be
matched. Similarly, the colour of a gemstone too depends very much on the
light that falls on it. It will appear very different when viewed by
candlelight, in sunlight or in the glare of a fluorescent lamp. Jewellers
and gemmologists therefore take the sun's rays to be several colours.
Electric lamps whose light spectrum is as close to sunlight as possible are
necessary for gem grading.
Another problem faced by gem buyers is that colour perception varies
considerably with each individual. Indeed some humans and all dogs are
colour-blind. Sensitivity to colour too varies as a result of the internal
structure of the eye. The human retina consists of rods and cones. The cones
are of three types, those sensitive to red and yellow, other to green and
yet others to the blue to violet regions of the light spectrum. The
sensitivity of these differs from person to person and therefore colour
judgment can be very subjective;this can affect the estimated price of a
gemstone significantly. Although one jeweller may sell in good faith a ruby
that appears to him as a pure red and so of high value, a second valuer may
see a trace of blue in the same stone and thus declar it to have a much
Colour appears to affect well-being and behaviour. It affects man in a
combination of biological, physiological, psychological, social and cultural
factors. For instance, magenta, red, orange, yellow, and yellow-green are
warm colours associated with excitement, happiness and comfort. Cool colours
include violet, blue, light blue, cyan and sea green and induce calm abd
peace as well as sadness, withdrawal and repression. Scientific studies show
that red light is more likely to produce epileptic seizures than blue light.
Red also increases blood pressure, respiration and heart rate. Naturally,
people connected the lustre and the colour of gemstones with medicine,
astrology and emotions. Even today, in an age of scientific cynicism, men
and women wear gems for their mystical ability to endow health, wealth and
happiness. The belief that gems possess magical properties has led to a huge
volume of oral traditions and literature, apart from billions of dolloars
worth of trade and industry. To increase profits, jewellers have devised
various processes than can improve or even change the colour of a gemstone.
These are described in a later chapter.