Complex sentence: It was the kilns at Arita formed the heart of the Japanese porcelain industry, which developed in the 17th century, after kaolin was discovered in 1616 by an immigrant Korean potter, Yi Sam-pyeong, also known as Kanage Sambei (1579--1655).
Split into simpler sentences: It was the kilns at Arita which formed the heart of the Japanese porcelain industry. Arita's kilns were set up in the 17th century, when kaolin was discovered in 1616 by a Korean potter, Yi Sam-pyeong, also known as Kanage Sambei (1579--1655).