In this video, a crimp-edge molding tool sandwiches the glass between a solid form on the inside and metal jaws on the outside to create a quatrefoil shape. This technique would be the last step in the making of a quatrefoil goblet.
This quatrefoil opening was created by a curious technique and a specialized tool. More common is the fin mold. The quatrefoil shape is created with a tool with two parts: an inner part and outer jaws that squeeze inward. This is the last thing to be done in the process of making the goblet.