Antonio Stradivari has long been thought to have been an apprentice of Nicolò Amati, but census documents do not list Stradivari as a garzone (shopboy) in the Amati household. Stradivari's early instruments do show the stylistic influence of the Amati, but as Girolamo II and Nicolò were the principal makers in Cremona during Stradivari's formative years, it would be natural for Stradivari to have been influenced by their work. Antonio Stradivari worked with two of his sons, Francesco (1671-1743) and Omobono (1679-1742), and today over 600 instruments survive from this prodigious workshop. Stradivari experimented with the shape and arching of the violin and made instruments according to many dimensions and proportions during his long career. Stradivari employed flatter arching than his predecessors, and this contributed to the production of a more powerful tone. During the period from about 1700 to 1720, Stradivari produced many of his finest violins and this is known as his "Golden Period."