A prunt is a small blob of glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

fused to a piece of glass. Prunts are applied primarily as decoration, but also help provide a firm grip in the absence of a handle.

Types of prunt

raspberry prunt:
A prunt impressed to the shape of a raspberry
lion's head prunt:
A prunt impressed to the shape of a lion's head
blackberry prunt:
A prunt impressed to the shape of a blackberry