Play of Color
by Nasrina Parvin Khan
A well-known Play-of-color gemstone is opal. Opal is an amorphous from of silica (sio2, nh2o). It is made up of sub microscopic spheres of silica with a little amount of water and air trapped in the spaces between these round spheres.
What is Play-of-color?
Play-of-color is a unique special optical phenomenon. This phenomenon is usually exhibits by the gem opal. The iridescent color effect in opal described as Play-of-color. Color of rainbow can be seen in gems by this optical phenomenon. But the displayed colors are unrelated to the gem’s own body color. So, we can guess that the structural pattern of gem is responsible for this colors creating optical phenomenon. Due to the structural pattern the light interfere or diffract in gems and produce the color phenomenon named as Play-of-color.
Play of color in Opal
A well-known Play-of-color gemstone is opal. Opal is an amorphous from of silica (sio2, nh2o). It is made up of sub microscopic spheres of silica with a little amount of water and air trapped in the spaces between these round spheres. The amount of water in opal may be 3% to 21%. But the precious opals have 6% to 10% water content usually.

Opal is a sedimentary stone. In the time of formation of this stone, oozing water through the earth dissolved in silicates and become rich. The silicates are deposits as minute spheres when the water enters in a cavity.
The transparent spheres of amorphous silica and the voids between them form a 3D grating. This structural pattern is the reason of interference and diffraction of light from the surface or the interior of gems. This property helps to display multiple colors as the angle of incident light changes. The openings act as the diffracting gratings, which split the light into colors, and the layered structure creates interference. The passing light through the stone breaks into various colors. So, we can say diffraction of light take place by layers of silica spheres in its composition and it is responsible for the phenomenon play-of-color.
Shifting patches of spectral colors seen on the surface or in the interior of gem due to the phenomenon play-of-color. Reflected lights from different layers of silicon slightly overlap from sync waves and help certain spectral colors to decrease or remove and reinforce others. So, we get a group of shifting colors that have a trembling on and off effect. The patches of colors moved when the gem is turned around. The effect just like to a bubble with rainbow color, just more dramatic.
Large openings between the spheres do not allowed the light to bend when passing through them. That is why no diffraction takes place and we get common opal. Random shape and arrangement of spheres also produced common opal. Shape, size and regularity of the spheres influenced the colors seen. It also depends on the angle of view. Uniform shape and size of spheres diffract light and help to produce precious opal. On the other hand, smaller size of spheres helps to see more blue and violet colors. But the spheres must be smaller than 1500 angstroms. More reds and oranges are seen with bigger sized spheres. But the spheres should not be larger than 3500 angstroms.
Opal gets the name for its special optical phenomenon Play-of-color. The name came from Greek word ‘opallus’, which means to see a change in color. The quality of opal justified by the number of color exhibited by the gems. The most valuable opal is ‘black-opal’. Which has a strong play-of-color. Different types of colors flashed brilliantly by this stone. Due to dark background color it has given the name ‘black opal’. The colors of black opals are black, dark green, dark brown and others. These gems are transparent to translucent.
There can be seen many other opals, like white opal, crystal opal, fine opal, cherry, water opal and etc.
White opal is transparent to opaque. It has white background with Play-of-color. Crystal opal has no background color with strong play-of-color. This stone is transparent to translucent and lets the light pass through it unlike others. Fire opal is also transparent with yellow, orange, red or brown background color. It may have play-of-color or not. Fire opal with red background color is also known as cherry opal. Water opal is transparent to semitransparent with colorless background. It has little or Play-of-color.
The point of color seen in opal due to the Play-of-color is called as “fire”. The term ‘flash’ used to refer sudden play-of color as stone moved.
Gemologists divided the phenomenon play-of-color in various types, like pinfire, mosaic, flame, peacock etc. A minute, close-set flash of color is called as pinfire. A large, regular, angular, close-set flash of colors is known as mosaic. Sweeping reddish bands across the gem is called flame, whereas blue and green color effect is known as peacock.
See Also: Color Effects in Gems , Asterism, Chatoyancy
External Reference
Usually, people confused with two special optical phenomena in opal. But play of color and opalescence are two different phenomenon of opal.

There are hundreds of Coral species. Many of them, Euphyllia Torch Coral, Mushroom Corals, Star Polyp Corals, Flower Corals to name a few are cultured by hobbyists, who want to grow corals at home in large tanks. These corals are sold over the Internet also. Marine scientists are still discovering new corals, which grow at depths below 800 feet. Corals, which comprise chiefly of Calcium Carbonate, grow in shallow, warm waters, which allow the sunlight through to help in Photosynthesis. But certain types of Corals have been found in cold water also.
Gift someone celebrating their 35th anniversary, a set of coral rings. One for him and one for her. Yes! Men can wear coral rings too – a big stone set in a square design will complement dark suits with aplomb. Before you make a purchase of Coral Jewellery, you must have some knowledge about this gemstone. There are many imitation corals available -dyed glass, plastic, shells and even heat-pressed and resin treated coral powder is passed of as authentic coral. While buying corals rings, let the length of your fingers and hands decide what will suit you the best. Try on different shapes set in various settings before deciding on a ring. The size should be perfect and the stone should be firmly set in the ring. Corals can be combined with other gems also depending on the colors you like – Pearls, Turquoise, Lapis Lazuli – the choice is varied. A coral stone set in Gold, Silver or Platinum will be an investment in Jewellery you will never regret.
An ancient magic stone from the ocean. The coral is taken from the Coral trees that are created in shallow warm or cold ocean waters by tiny living creatures called Polyps. Millions of years are taken to create the coral reefs, which yield these gorgeous gems. Being organic in nature, corals are delicate and break more easily than other gemstones. These gems are found in a several colors – Gold, Black, Blue, White and in an assortment of shades of Red, from pinkish to deep blood red. The Black, Blue, White and Gold corals are rare but the red corals are available in abundance, although the superior quality deep red corals that are highly valued by connoisseurs are rare and command a high price. The best of these red corals are found in Japan and Italy.
Coral Jewellery does not need high maintenance. The gem is fragile and more brittle than other gems. It measures only 3.5 on the Mohs scale and the splendor of the coral will diminish if not taken care of. Like Pearls, Turquoise, some corals can be porous -these gems will get damaged if immersed in water for too long. Take care not to use too much water while wearing coral bracelets or rings. The water may also dull the polish of the coral making it look lackluster and unattractive. If you plan to go swimming, remove your Jewellery before diving in. The chlorine present in the water can cause the corals to spoil.
Regularly check the stones in your Jewellery. If any of the stones are loose, visit your jeweler and have him fix it before you loose one expensive coral from your ring. Beads in a Bracelet or Necklace should be re-strung professionally, if they break. Place your coral beads flat inside a soft, velvet pouch. Clasps are important – tug gently at your Necklaces /Bracelets after wearing it so you are sure the clasp is firmly in place. Loose clasps can result in lost Jewellery.
Coral seems to be an excellent choice for jewelry. But, have you ever thought that where from coral comes actually? Coral is a sea product that grows in branches, which look much like dwarf underwater trees. In the whole cycle of making of coral, a marine gelatinous animal collects calcium carbonate around its body. It is a polyp made of calcite fibrous crystals.
You also have to be careful in picking the right coral. Must buyers of coral end up in getting some other materials that are used to imitate the natural coral. There are all the chances for you to be mistaken with Plastic, man made Coral, Howlite, Shell, Ivory, Onyx/Calcite and Fossil Ivory as Coral. For Conchiolin Coral, the materials like plastic, Chalcedony and Jet are used for imitation.

Stones with a clear blue color – without green or gray – are generally the most valuable. Though almost all gemstones contain some degree of blemishes, the highest quality Aquamarine is transparent, with no internal flaws or external imperfections. Aquamarine is a hard durable stone (7.5 to 8), which makes it a good choice for jewelry that is worn frequently like rings; and is readily available in larger sizes. It is especially dramatic when cut in a rectangular or oval shape, with facets, many angled sides or cut as a cabochon – a smooth dome without facets.