Up to the fourth century, jewelry was known only in it rough, or crystalline forms. It came in a variety of shapes, the most common being the octahedron. This was a crystal with eight faces, resembling two pyramids joined at their bases.
While the weight of diamond bracelet is important, it doesnt necessarily provide the "perceived size" of princess cut diamond. A shallow cut diamond will have a greater diameter, and will therefore look larger.
When fancy diamonds is cut too deep light leaks out the bottom, brilliance is lost, and the princess cut diamond will appear to be dark.