You can see a video of his process below. The experimentation started with fish tank clarifier, which is — apparently — mostly alum. Alum’s been used to treat wastewater for a long time.

It turns out that a hot solution of alum (ammonium aluminum sulfate), which is available in the spice rack of your local supermarket, will dissolve the steel drill bit without reacting with the brass.

chemically known as potassium alum or aluminum potassium sulfate, exhibits astringent properties when applied to the skin.