There are two standard types of windmill on Denby jugs -see below. The left one would appear to be the earlier but there is considerable overlap. The earliest dated example seen of the left one is 1826 and the earliest dated example of the right one seen is 1840. Generally the left  hand windmill appears on half and some one pint jugs and the right hand one on the larger sizes. The only exception seems to be a series of uniformly dark jugs with almost black sprigs which only seem to use the first type. They are quite different in style and could be Brampton products (click to view). A sprig showing what looks like a toy windmill on a table has been seen on early jugs and tankards in conjunction with other standard Denby sprigs. (Click to view).

Both main types were modified some time in the twentieth century by covering their foregrounds with flowers.