How can you say that the Gupta period made great progress in the field of metallurgy?

The Gupta period saw significant advancements in metallurgy, highlighted by the Iron Pillar at Delhi, which has remained rust-free for many years, showcasing advanced ironworking. Gupta artisans also excelled in metal casting, producing intricate copper statues like the Sultanganj Buddha and Nalanda Buddha, demonstrating their skill. Additionally, they minted fine gold coins with detailed designs, reflecting their expertise in precious metals. These achievements, including innovative alloying and smelting techniques, illustrate the Gupta's mastery of metallurgy, influencing future generations.