The use of a drop ring is a technique for shaping glass in a kiln.
The most common approach to a drop ring uses a wide ceramic or refractory fiber ring that is raised above the kiln shelf or floor using kiln furniture. Glass is place on the ring so that when the temperature is sufficiently high enough the glass will sag through the hole. The usual result is broad-rimmed bowl.
One key to success is to make sure that there is a sufficient area of glass on the surface of the ring (i.e. not over the hole) so that the edge of the glass is not pulled through the hole as the glass sags.
When firing glass on a drop ring, most artists will pay close attention to the progress and vent the kiln (crash cool) when the glass has reached the desired shape.