| Gemstone
Library |
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| Colors |
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| There are three main components of color that affect gemstones: hue,
saturation, and brightness. We need all three of these components to be able to fully
describe color. |
When we say "color" we are often talking about hue.
It is the component of color we talk about most. It indicates whether a color looks red,
green, blue, yellow, orange, etc.
As an example, look below at the line of different hues. Notice how they look like colors
from a rainbow. |
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| Hue values range between 0 and 360 degrees. They take on these values
because they are placed around a circle. |
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| The Number of Colors: National Bureau of Standards (US) lists
267 color names. Berlin & Kay (1969) studied color terms in 100 languages and proposed
that there exist 11 universal color terms: white, black, red, green, yellow, blue, brown,
purple, pink, orange, gray. This result was confirmed experimentally in American observers
by Boynton & Olson (1987), and in both Japanese and American observers by Uchikawa
& Boynton (1987). The number of discriminable colors probably exceeds 10,000. Not all
discriminable differences are separated into different color categories (names). |
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Saturation represents how pure a color is. As an example of
saturation, think about rubies color increasing the saturation will change the color from:
deep red -> vivid red -> intense red -> red -> pinkish-red. |
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| Saturation |
100% |
90% |
80% |
70% |
60% |
50% |
40% |
30% |
20% |
10% |
0% |
| Appearance |
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| Brightness tells us how strong a color is. For example, the sun
has a high brightness, while a birthday candle has a low brightness. Colors like whites
and yellows have a high brightness. Colors like browns and grays have a medium brightness.
Colors like black have a low brightness. |
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![[Sample Brightnesses]](http://www.ajsgems.com/gemlibrary/image/smpbrght.gif) |
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| As an example, here are several bluish squares. As you go from left to
right they increase in brightness. |
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When we talked about hue we said that hue values are between 0
and 360 degrees because they are frequently laid out around a circle.
If we lay them out around a circle and also increase the saturation as we move away
from the center, we get the circle shown below. The hue changes as we go around the
circle, and the colors also get more saturated as you move towards the edge of the circle.
In the center they are very faded; near the outside of the circle they are very pure. |
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| If you change the circle to a cylinder, along the axes of the
cylinder, the change in brightness can be shown |
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| Additive Color Mixture: Here are two demonstrations of additive
color mixture. In the figure on the left the primaries are red, green and
blue. Where they all overlap (the bulging triangular region in the center) they
combine to produce white. The demonstration on the left illustrates that any three primary
lights (in this case a cyan, a purple and an orange) can similarly be used to produce
white. |
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