This beautiful vase was 3D printed in glass through 3D printing shop Shapeways, then finished with leaded glass enamels: "When designing hollow parts accommodations must be made to allow the support powder to completely fill all empty spaces. The support powder acts as a mold during firing. The glass becomes like soft toffee during firing and without support it will move in unexpected (usually disastrous) ways.
These are things we know for fact."