My previous post described how I use the technique of Cross Polarization to create colorful images of birefringent crystals.  This technique reveals details of the underlying structure of the crystal itself.  It also effectively color codes different parts of the crystal.  These patterns and colors not only contain useful information for scientists who study their properties, they also reveal the beauty of the natural world around us.

The color of the light passing through these crystals can be further enhanced by placing a Full Wave Plate between the first polarizer and the sample.  A Wave Plate is an optical component, in this case a piece of specially designed plastic, which changes the polarization of light passing through it.  How much the polarization changes depends on the color of the light.  If you read my first post this will sound very similar to the birefringent effect of the crystals.  Indeed the physics is the same.  What is different is that a wave plate is carefully designed to produce a very specific change to the polarization of the light which passes through it.

Trying to explain what a full wave plate does to the light passing through it is well beyond the scope of this post.  Its effect however is that can be used to ensure that certain very specific colors of light will end up being blocked by the second polarizer in the cross polarization technique.  White light is what our eyes see when all colors of light are present.  When one or more colors are blocked from reaching our eyes, the result is we see the complement of the blocked colors.

Putting aside the physics of electro-magnetic waves and color theory, the aesthetic effect of adding a full wave plate between the crossed polarizers results in beautifully vivid colors in the images as seen below.

Each of these images shows the result of a different combination of rotations of the full wave plate and the polarizer which sits atop the light source.  Note how both the background color and the colors in the crystal change.