Wikipedia - Luca Della Robbia
Luca della Robbia (1400-1482) was an Italian sculptor from Florence, noted for his terracotta roundels.New Advent Catholic Encyclopedia - Andrea Della Robbia
Luca Della Robbia developed a pottery glaze that made his creations more durable in the outdoors and thus suitable for use on the exterior of buildings. His work is noted for its charm rather than the drama of the work of some of his contemporaries.
Andrea Della Robbia - Nephew, pupil, assistant, and sharer of Luca's secrets, b. at Florence, 1431; d. 1528. It is often difficult to distinguish between his works and Luca's.