The glassmaker’s craft of using an “optic mold” to create desired interior textures and designs was invented by Roman glassworkers and flourished in Venice in the Middle Ages. Using this ancient “optic” technique, house a glass bulb in a hand-blown oval diffuser. This diffuser is perfectly clear on the outside with a wavy horizontal pattern working on its bulb-facing side. These interior lines are in the “optic” tradition, valued in heritage pieces such as Depression glass.