Disposable crucibles eliminate the need for time-consuming cleaning procedures and the possibility of cross-sample contamination. Regular-purity crucibles are made of graphite with impurities ranging from 10 to 100 ppm each of Mg, Fe, Al, Si, and Cu. They are well suited for most basic borate fusion applications. High-purity crucibles are made of graphite with total metallic impurity limits of 2 ppm—ideal for trace-level analytical work.