An unprecedented number of documents, dating from between 1483 and 1521, refer to a certain stained-glass artist João, then called master, who was contracted as royal stained-glass master of the Monastery of Batalha. During those thirty-eight years we have not found reference to any other artist working in this area at Batalha. So who was master João? Some believe he was Flemish. None of the documents that exist today, however, allude to his nationality.
There is documental evidence that the remains of stained-glass dating from 1508 found in the sacristy of Batalha belong to master João. While they do not contradict the accounts of 14th century tradition of the old Low Countries (preserved in scarce examples), they are also not sufficient to be able affirm any particular artistic style. Nevertheless, the way in which they were painted is close to fragments of the Last Supper and the Wedding at Cana which are attributed to the artist. Eminently pictorial, the style of these works faintly evoke the painting on glass of the second half of the 15th century, in Brabant and, in part, Flanders.
What the art of master João did was introduce once and for all in Batalha the artistic breakthroughs of the painters of the northern Renaissance, in a visual style more reminiscent of these traditions than later works found in the chapter and the main chapel.