We assume this means physical brightness, and we imagine that the custodians of the Plates maintained a watchful care over them. Brass, as it is known today, an alloy of copper and zinc, is not meant by the term used in the Bible or Book of Mormon, as zinc was not then known. The word means copper, and in some places in the Bible it is used to signify a simple metal, such as bronze, an alloy of copper and tin. We judge that the Plates of Laban being made of brass, were largely copper, and as copper has a tendency to corrode, or to wear away gradually, as by the action of strong acid, we believe the Brass Plates were in need of constant care. The same result is found when oxygen which is in the air we breathe comes into contact with copper as with iron, it causes the iron to corrode or rust away. Therefore, the necessity of keeping clean "all the plates which do contain that which is Holy Writ" so that in the end after passing through the hands of many keepers, they will remain bright as when they were new.