Corn syrup may be sending us toward a slow death, but in the meantime, it can create pretty swirling colors. Why? Because it's an optically active material, and can turn polarized light into a rainbow.
When light comes in from the sun, or from conventional light bulbs, its waves are jiggling in all different directions. Pass it through a polarizing filter and it will only be vibrating in one direction. Polarizers don't need to be high tech. They can be as simple as a smooth reflective surface. Smooth surfaces tend to reflect light that's vibrating parallel to them, so the light bouncing off a pond or a car hood - both of which are horizontal - will reflect horizontally polarized light. This is why polarized sunglasses cut down on glare. They can be made to filter out polarized light, and so block most of the light coming from shiny surfaces.
When light goes through a polarized lens, or bounces off a surface and becomes polarized, it may be vibrating in the same direction, but it's still white light. Karo syrup changes that. Get polarized light by putting it through a filter, and then look through a clear jar of Karo syrup. Nothing so far, but grab another polarizing filter. As you rotate that second filter, the Karo syrup will suddenly turn different colors.
How does a polarizing filter, which can do nothing except take out light that's jiggling in the wrong direction, suddenly turn this syrup different colors? Because the syrup is, coincidentally, an example of an "optically active" material. These materials do something strange. When polarized light comes into them, they slowly rotate the wavelengths of light. And they rotate the light different degrees depending on its wavelength. Blue light will rotate more than red light, because it has a shorter wavelength. So although the different wavelengths that make up the white light enter the syrup all vibrating the same direction, the different wavelengths are twisted to different angles when they come out of the syrup. When you hold up that second polarizing filter, you are filtering out some colors. As you turn it, you filter out different colors, which makes the syrup turn different colors.
Just as note - organic glucose molecules rotates the light clockwise. Glucose molecules made in a lab rotate it counterclockwise. Nobody knows why this is.
Top Image: FotoosVanRobin
[Via The Exploratorium]