A bell-shaped terracotta rhubarb forcer with lid, about 13" high
I have been taken to task by one of my garden history colleagues for being politically incorrect in my biased presentation of glass cloches. He is correct, of course. The only fair thing to do here is show you the other types of cloches from the 17th, 18th, & 19th centuries, some still in use today. They do deserve equal time. In this political season, this is my attempt at trying to be "fair & balanced."
Handmade terra-cotta cloches have existed nearly as long as the blown-glass examples. They often have ventilation holes to prevent spoilage from excessive heat & humidity.
Gardeners often used terra-cotta cloches slow the growth of lettuce.
Terre cotta rhubarb pots at Knightshayes Garden, Tiverton, Devon, England
Other terra-cotta cloches, often about 30" high & similar in shape to chimney pots, were used for forcing rhubarb. Some of these had lids.
Barnsdale Gardens, Exton, Oakham, Rutland, England.
Gardeners also used metal-framed glass cloches during the period.
In metal-framed cloches, one of the glass panes could be removed by the gardener for fresh air ventilation. Sometimes gardeners temporarily would paint the glass white to shade tender plants from direct sunlight.
Audley End Kitchen Garden, English Heritage, Essex, England
Today, these architectural tents or pavilions are more often employed for decorative purposes.
I found only one depiction of a completely metal cloche made in France about 1900.
Let me close by admitting what you surely already realize, I just love those plain, bell-shaped glass cloches...