After the competition, Ghiberti's father Bartolo assisted him greatly in perfecting the design of his door before it was cast. This commission brought immediate and lasting recognition to the young artist. In 1403 the formal contract was signed with Bartolo di Michele's workshop, the same workshop he had previously been trained in, and overnight it became the most prestigious in Florence. Four years later in 1407, Lorenzo legally took over the commission and was prohibited from accepting additional commissions. He devoted much of his time to creating the gates, and was paid two-hundred florins a year for his work. To cast the doors, Lorenzo worked in a studio named the Aja or Threshing floor. The studio was located near the Hospital of Saint. Maria Nuova, the oldest hospital that is still active in Florence today. At the Aja, Ghiberti built a large furnace to melt his metal in an attempt to cast the doors, however his first model was a failure. After this trial, he attempted once more to make a mold. On his second try he was successful and ended up using 34,000 pounds of bronze, costing a total of 22,000 ducats. This was a large sum in this time period.