How diamonds sparkle

Refraction

Just like the graphite of pencil leads, diamonds are made of carbon. However, the arrangement of the carbon atoms in diamonds is significantly different from that in graphite. Diamonds are very hard. Diamond chips are therefore used for cutting glass or for drilling. The diamond powder is very suitable for grinding. Diamonds were formed from carbon at high temperature and high pressure. Today it is possible to produce artificial diamonds.

Most people are familiar with the diamond as a piece of jewelry. For example, the crown on the right is richly decorated with diamonds. When these are properly sanded, they sparkle very nicely. Often the light is also broken down into its spectral colors.

Rough diamonds can be found in South Africa and Ceylon, among other places. Cutting the diamonds requires a lot of experience and craftsmanship. A diamond cutting center is in Amsterdam. The picture below shows a very nicely cut diamond.

The sparkle of diamonds is based on the fact that the light hitting them is very often totally reflected in the diamond. Two facts are decisive for this:

  • The high refractive index of diamond.
  • The skillful cut of the diamond.

Explain what the diamond's high refractive index means when it passes from air to diamond.

Determine the critical angle of total reflection for the transition from diamond to air. Use the diagram on the basic knowledge page.

With a high refractive index, the beam coming from the air is very strongly deflected from its original direction.

The diagram shows that at \ ({\ alpha _ {\ rm {L}}} = 90 ^ \ circ \) the angular width \ ({\ alpha _ {\ rm {D}}} = 24 ^ \ circ \) is.

Compared to water, the critical angle of total reflection is much smaller with diamond (water: \ (48 ^ \ circ \); diamond \ (24 ^ \ circ \)).

At the transition from the optically denser to the optically thinner medium, the rays approaching A are refracted from the yellow area into the air, which is totally reflected from the bluish area. You can see that the proportion of totally reflected rays is significantly greater with diamond than with water, for example.

A standard cut of a diamond creates 58 surfaces. If the position of these surfaces is correct, then the incident light is almost completely totally reflected in the diamond and essentially escapes from the diamond again in the direction of incidence. This creates the sparkling, glittering impression.

The following pictures show the course of the rays in a properly cut diamond (left), in a diamond that is too flat (center) and in a diamond that is too thick (right).

The four C's in diamonds

The so-called four determine the quality and thus the price of a diamond C.'s:

  • C.ut (cut): A well-cut diamond, regardless of its shape, reflects the incident light better, it is "more brilliant" and has more "fire".
  • C.olour (color): The most expensive diamonds are the completely colorless ones, as they can be easily penetrated by light.
  • C.larity (purity): Most natural diamonds have small inclusions. The fewer and the smaller these inclusions, the better the light can penetrate the stone.
  • C.arat (weight): The weight of a diamond is given in carats. One carat is 0.2 grams.