Old European cut diamonds and modern brilliant cut diamonds are two different ways of cutting diamonds, and they are very different in appearance and cut.

Old European cut diamonds are an ancient cutting method that first appeared in the 17th century. This cut is characterized by a rounded shape with a deeper base and a flatter top, resulting in a soft sheen on the surface of the diamond, known as a "wax shine". The advantage of this cutting method is that it can retain the weight and volume of the original diamond to the maximum extent, but the disadvantage is that the luster is not bright enough, and the fire and sparkle of the diamond are not as good as modern brilliant-cut diamonds.

Modern brilliant-cut diamonds are a relatively new cutting method, appearing mainly in the early 20th century. The characteristic of this cutting method is that the shape of the diamond is relatively regular, with a shallow bottom and a sharp top. Therefore, the surface of the diamond shows strong fire and sparkle, which is called "sparkle". The advantage of this cutting method is that the diamond has a bright luster, high fire and sparkle, but the disadvantage is that it wastes a certain amount of weight and volume of the original diamond.

Characteristics of old European cut diamonds:

Shape: Old European cut diamonds usually have a rounded shape, closer to the traditional round shape.
Depth: A deeper base makes the diamond appear thicker on the sides.
Surface luster: Old European cut diamonds exhibit a soft luster, known as "wax shine". This luster is not as bright and sparkling as modern brilliant cut diamonds.
Weight retention: The design goal of old European cut diamonds is to retain the weight and volume of the original diamond to the maximum extent to reduce waste.
Characteristics of Modern Brilliant Cut Diamonds:

Shape: Modern brilliant-cut diamonds usually appear in regular shapes, such as round (Brilliant Cut) or square (Princess Cut).
Depth: A shallower base makes the diamond look flatter on the sides.
Surface Fire and Brilliance: Modern brilliant-cut diamonds are known for their intense fire and brilliance. This is achieved through precise cutting and optimization of light.
Light Reflection: Modern brilliant cut diamonds are cut to maximize the reflection and refraction of light, making the diamond appear brighter and more sparkly.
Cut comparison:

Luster and brilliance: Modern brilliant-cut diamonds generally have higher luster and brilliance due to their optimized cut, allowing them to show more fire in different lights.
Appearance shape: Old European cut diamonds are closer to the traditional round shape, while modern brilliant cut diamonds can have more shape options, such as round, square, etc.
Diamond weight retention: The design of old European cut diamonds seeks to retain the weight and volume of the original diamond to the maximum extent, while modern brilliant cut diamonds may waste a certain amount of the original diamond weight and volume in pursuit of better optical effects.

There is a big difference in appearance and cut between old European cut diamonds and modern brilliant cut diamonds. Old European cut diamonds are characterized by a rounded shape, a deep base, and a soft surface, while modern brilliant-cut diamonds are characterized by a regular shape, a shallow base, and a bright surface. Which cutting method you choose depends largely on personal preference and needs.