Developed in 18th century Europe old mine cushion cuts were not round but had a slightly curved edge which formed a soft square. They were made with a variety of facet patterns but always with a small table, high crown, and larger culet. Giving them an architectural look.
This cut gave way to more modern faceting. While cutting a higher crown makes for a beautifully shaped diamond it takes away too much carat weight. Which these days tends to out weigh other aspects which were more prized in the past.
These diamonds were cut virtually by hand before the invention of modern bruting and the motorized saw and therefor have a more natural unprocessed look. These stones will almost never be as white and brilliant as new stones. If you compare one of these stones to a modern brilliant cut, you will notice the pattern reflected has more sculptural triangles rather then slivers of light. Warmly known as old miners by people in the know these are one of the most prized antique diamond cuts.