workshop and group
In one sense, group refers to a list of vases which have common elements, yet cannot be assigned to a specific vase painter. In the sense we use group, it refers to a group of painters whose work/style is similar, and in this respect, group is almost synonymous to workshop. These painters may have worked side-by-side or may have simply been contemporaries. The question that arises is how directly one painter influenced another. Workshop is used to define a direct working relationship between painters and can be used with certainty when it is known that two painters collaborated on painting a single vase. It is probable that many groups actually represented workshops, but it is very difficult to prove.