Oh what did they do in Paris?
Per the National Museum Wales, they say here:
"During the Middle Ages, several regions of France exported pottery to Britain - notably northern France, Normandy and the Ardennes. Most of the French pottery found in Wales came from the Saintonge area of south-west France.
The trade in pottery from the Saintonge area to Britain began early in the 13th-century and lasted for about 500 years. At the start of this period the English ruled neighbouring Gascony, and many of the vessels that have been found in Wales probably made their way to Britain from the ports of La Rochelle and Bordeaux as part of mixed cargoes (wine being the most important commodity).
Pottery from the Saintonge area was made from a fine clay that was well suited to the throwing of light, thin-walled shapes such as those seen here. The clay also had a low iron content, which meant that, when fired, it produced a vessel with a white or buff fabric."
Per the British Museum here:
"The clear glaze and the choice of greens and browns used to decorate the body of the jug may well have been influenced by Italian pottery, particularly from Orvieto. The distinctive pulled lip spout and the decorative motif of the bird and shields are both features which commonly occur on Saintonge products of this type."
Here are some examples of this type of ceramic jug: