Crystal is made by adding lead oxide to glass, which makes crystal heavier than glass. The lead in crystal is what makes it sparkle and reflect colors much more than plain glass. When the lead content is higher - the crystal is a better quality.
In Europe, glass must contain at least 4% lead to be called crystal.
In the US, glass must have at least 1% lead content to be classified as crystal.
In contrast, Swarovski (Swore-off-ski) crystal has at least 30% lead content.

Swarovski crystals are regarded as the highest quality machine cut and polished crystal beads in the world. Swarovski crystals are perfectly uniform. This means that the height, width and slope are consistent.

Swarovski uses machinery that precisely cuts each crystal. They cut hard materials such as crystal and gems, in a way that they have a hundred identical facets in several directions.
This a very complicated task: each direction of the reflected light must first be calculated by computer, simulated in 3D, optimized and finally converted into control programs for complex machinery. The precision cutting of Swarovski machinery allows each crystal to have its facet juncture "pointing up". This means the facet junctures all meet at precisely the same point. This is a similar aspect of diamond faceting. Swarovski crystals with an AB finish have a uniform surface luster.

There are no swirling marks from the vacuum process that produces the AB finish, and generally there are no scratches. When you look inside Swarovski crystals, you will see no bubbles.