A very rare borate mineral which, in the real world, was discovered in Myanmar in the 1950s and named after mineralogist and gem dealer Arthur C.D. Pain. For Warehouse purposes, however, it infuses the entire Warehouse structure, causing any who carry the chemical injected into them, like James MacPherson, to have their blood turn acidic and consume them from within. The only known protection is a crystalline necklace containing palladium, such as the one MacPherson wore whilst 'invading' the Warehouse with H.G. Wells.
- Although painite and any potential effects it has on the human body are unknown, it was likely chosen as a chemical deterrent to Warehouse infiltration due to its red color and, presumably, the "pain" in its name.