Eternity rings have stones that circle the entire ring. It is meant to symbolize never ending love and affection. These rings are generally made of gold with diamonds or some other gemstones inset (rubies, sapphires and tanzanite are all popular). Because only half of the stones can be seen at a time, the half ring was developed that has stones only on the facing side of the band.
The idea for the eternity ring began in ancient Egypt (as early as 2000 BC). Most of the early rings were half rings. A common design for these involved a snake swallowing its tail which helped to solidify the notion of the ring as a symbol of eternity.
Princess and emerald cuts are the most popular for the individual stones in the eternity ring because of compactness of their shape. The stones are normally cut smaller than they would be for an engagement ring because it would be uncomfortable to wear such a ring when the stones rub against other fingers.
There are a few popular setting styles. Settings of stones in a channel is very common because it is easy to secure the stones this way and it is also more comfortable to wear than settings that utilize prongs. In a bar setting a bar of gold or platinum is laid between each gem. This gives an elegant effect and reduces the number of stones necessary to complete the ring. Other setting patterns can be used such as the curved-S pattern, bezels, or even figural settings with vines, leaves, flowers, or the traditional snake.
Most eternity rings are purchased to commemorate a long-standing relationship. They are highly recommended as an anniversary gift, and are also an elegant gift to give on the birth of a child. They sometimes can take the place of older wedding or engagement rings and can be worn on the ring finger of the left hand as a replacement for one or both of these rings. They can also, of course, be worn on any other finger (or even a thumb).
Because of the continuous stone settings, eternity rings are usually custom made to a particular size. While this can be a disadvantage when there are time constraints. This allows for a great deal of customization, like including birthstones of children. Continuous stone settings also can create a problem if the ring ever needs to be resized as cutting out or adding a stone can be expensive. Even so, a plastic resizer can be worn with rings that are too large to make them fit more snugly. This is also a good reason to purchase a "half ring" (with the stones only on the side of the ring facing out). By expanding or contracting the inside, the ring can be more easily resized.