People often ask me why an opal seems to change color as they turn it, almost as if there is a light inside. There is not. What you are seeing is called play-of-color, and it is the single thing that makes opal opal. After fifty years at the bench I still think it is the loveliest effect in the gem world. Here is what it is, why it happens, and what to look for.
What play-of-color actually is
Play-of-color is the shifting flash of spectral colors you see across an opal as the light or the angle changes. It is not a stain or a coating. It comes from the way the stone is built. Precious opal is made of countless tiny spheres of silica, all roughly the same size, stacked in an orderly grid. When light enters, that grid splits it into its spectral colors, the same physics that puts color in a soap bubble or on a butterfly wing. Because the effect depends on angle, the colors move as you move. For the wider story of opal, see my guide to understanding opal.
Body tone is not the same thing
This trips people up, so it is worth saying plainly. Body tone is the background color of the stone, from black through gray to white. Play-of-color is the rainbow that dances on top of it. They are two separate things. A dark body tone makes the play-of-color look more vivid, which is exactly why black opal is so prized, but the body and the play are still doing different jobs.
The colors, and which are rare
An opal can flash any spectral color, but they are not equally common. Blue and green turn up most often, which is why they cost the least. Orange is scarcer. Red is the rarest of all, and a stone that flashes strong red, especially red across a dark body, is the one collectors chase. The size of those silica spheres decides which colors appear: smaller spheres give the blues, larger ones reach all the way to red.
Want to see play-of-color in person? Browse the opal rings in my collection, each chosen for the life in its color.
Pattern matters too
It is not only which colors appear, but how they sit. Fine speckles are called pinfire; broad sweeps are called broad flash; and the rare, sought-after mosaic of close-packed segments is called harlequin. Broad, bold patterns are scarcer than pinfire and priced accordingly. When I choose a stone I am weighing brightness, color and pattern all at once, and brightness usually wins the argument: a vivid stone with a simple pattern beats a dull one with a fancy pattern almost every time.
Play-of-color versus “fire”
One quick clarification, because the words get muddled. Play-of-color is the rainbow effect in precious opal. “Fire opal” is something else: an opal named for its warm orange-to-red body color, which may or may not show any play-of-color at all. If you have read about fire opal and wondered why it looked so different, that is why.
Frequently asked questions
Why does my opal change color when I move it? Because play-of-color depends on the angle of the light. The orderly grid of silica spheres inside the stone splits light into spectral colors, and which ones you see shifts as the angle changes.
What opal color is most valuable? Red is the rarest and most valuable play-of-color, then orange, with blue and green the most common. A strong red on a dark body is the top of the tree.
Does more play-of-color mean a better opal? Brighter, more even color is generally better, but value is a balance of brightness, color, pattern and body tone. See how much is opal worth for the full picture.
Color is the heart of every opal I set, and no two are alike. Browse the current opal rings, or talk to me about a custom piece built around a stone whose color you love.
