据《大清会典》记载，宫中共有大缸308口。但世事沧桑，由于各种原因，如今只剩下231口了。这些大缸共分为铁、铜和鎏金铜三种。一般来讲，铁缸是明代时铸造的；铜缸有明代的，也有清代的；鎏金铜缸则均是清代铸造的。其中，以铜缸居多，所以人们习惯地称宫中的大缸为铜缸。（铜大缸厂家）

According to the book of the Great Qing Dynasty, there are 308 large tanks in the palace. However, due to various reasons, there are only 231 people left. These vats are divided into three types: iron, copper and gilded copper. Generally speaking, iron jars were made in Ming Dynasty; copper jars were made in Ming Dynasty and Qing Dynasty; gold-plated copper jars were all made in Qing Dynasty. Among them, most of them are copper tanks, so people are used to calling the big tanks in the palace as copper tanks. (copper cylinder manufacturer)