All copies of a book, print, portfolio, sculpture, etc., issued or produced at one time or from a single set of type. Printed works can be made in an edition of between one and many thousands of copies. With most printing techniques the plate or screen will become worn if very many prints are made, so to maintain quality (and exclusivity) editions of original prints are usually kept below one hundred copies and normally average between thirty and fifty copies. Prints made up of several different plates can be extremely complicated and time-consuming to edition, so in these cases editions are kept low for practical reasons. Sculptural editions are a set of cast sculptures taken from the same mould or master. These editions are usually much lower, consisting of no more than six casts. Though each cast in an edition might have a lower value than a unique piece, it may be a more effective way of offsetting costs of an expensive process such as bronze casting.