I mentioned in a previous post how Greek pottery acts as a timestamp because of its constantly changing styles. Pottery shards at a site can narrow the site date down to a decade or so. Greek pottery on tour has equal value because, when the Greeks left home, they took with them (or had sent to them) pottery which was required for daily living so its debris at a settlement site can point to its origin.
Let's see why pottery followed the traveling Greeks.
Alien Greeks who did not have access to their own kilns would require pottery from back home. Sometimes local pottery was available but of inferior quality, again requiring imports. Of the various types of containers we have pottery for transport (e.g. amphorae for olive oil), large and small containers and utensils for the home, and objets d’art. The first and last of these types may or may not be reliable in pointing to the link between a Greek settlement and its point of origin. The middle category, however, is superior because, as a personal container, it would not be sold or traded.
Transport vessels were undecorated during the early archaic period and only began to show distinguishing marks in the seventh century. The finest of Protocorinthian painting appears on perfume flasks that were undoubtedly shipped by Corinth, but these containers also went to non-Corinthian settlements. This tells us specifically about what the Corinthians were up to but no one else.
With respect to objets d’art, the story is more interesting. In the mid-seventh century, the Corinthians were turning out so much beautifully decorated pottery the pieces began to be used in homes for decoration. Greek settlements in the west could not get enough of the stuff so they demanded more. The Corinthians, being good capitalists and responding to a supply demand imbalance, increased production and lowered the quality. Then, in the first quarter of the sixth century, Athens seized on an opportunity to win on quality, and began to market the first of their Black Figure vases. Trying to regain their position, the Corinthians countered with a line of beautiful mixing bowls, but they were unsuccessful. In all these cases, Objets d’art were not localized enough to build a link between Greek settlements and their mother city.