The composition of the starting material in the sample chamber, catalyst for the reaction, and the required temperature and pressure were little more than guesses. Hall used iron sulfide and a form of powdered carbon as the starting material, with tantalum disks to conduct the electricity into the cell for heating it. The experiment was conducted at about 100,000 atmospheres, 1600 °C and took about 38 minutes. Upon breaking open the sample, clusters of diamond octahedral crystals were found on the tantalum metal disks, which apparently acted as a catalyst.