Originally thought of as a waste product and a nuisance that had to be got rid of, mundic, also known as iron pyrites or fools gold, it is often found in copper mines and tin mines. Wheal Friendship was no exeption. When the copper became scarce the mine owners turned their attention to retreaving what they could from what had, until then, just been waste.

The women employed on the surface to break up the mundic, where known as Bal Maidens and there is still a Bal Lane in Mary Tavy. The crushed ore is heated in a furnace and the impurity they were after, arsenic, was allowed to condense on the sides of long flues that carried the smoke away from the fire and up a distant chimney. Those seen in the photo at the top are probably from the calciners in which the mundic was heated.

Arsenic and William Morris