A diatret glass (also called a cage cup) is a mostly bell-shaped, magnificent double-walled vessel with pierced glass. Diatreta consist of an inner beaker and an outer cage or shell of decoration that stands out from the body of the cup, to which it is attached by short stems or shanks. What is meant by this is that the body of the vessel is surrounded by a perforated glass mesh. The vessels are therefore also referred to as net cups or cage cups.

Cage glasses were valuable show glasses of Roman times; there were even ancient laws regulating the liability for damage caused by cup grinders. The first such glasses are known from the 1st century. The few known early examples of diatreta are not yet decorated with the characteristic network, but with different motifs. The art of glass cutting was at its peak in the 3rd and 4th centuries AD. More than 70 examples are known to date, many of which have survived only as fragments.

Cage glasses are mostly regarded as drinking vessels because they are often in the shape of drinking cups and are decorated with toasts like: “Bibe multis annis” (Drink [that you may live] for many years!). The use as a drinking cup is also handed down in a poem by Martial and was likely used as a special vessel at symposiums or other events. 

To date, the ancient art of manufacturing diatret glass remains unclear: When in 1906 German scientists attempted to cut a cage cup – and filled with champagne to test it – it is said that the rim broke immediately off when the cutter began to drink.