Burners made during the Xuande period (AD 1426 - 1435), are a great achievement in the Ming Dynasty. They are attached with the same importance as bronze ware of the Shang and Zhou Dynasties. In 1428, Emperor Xuanzong instructed the Ministry of Works to make bronze out of precious materials including brass, zinc and tin. Liquefied bronze was to be used for casting only after having gone through the smelting process twelve times. The resultant bronze is only one-fourth of the weight of the raw material. That is why Xuande bronze ware is admired for its exceptional purity and fine quality. Xuande burners were rare even during the Ming Dynasty, and were frequently imitated in the later periods. Imitations during mid-Ming Dynasty, in particular, were so well done that they could easily be taken for the genuine period pieces. Authentication of Xuande burners is therefore very difficult.