Sometimes, the barrier between the Material world and Limbo grows attenuated, and Limbic precipitation occurs. The turbulent lower airs seem especially prone to such penetration by shadow substances, and hence the limbic intrusion fall as an inchoate rain.
Typically, the precipitations come in the form of slime or foam, cold to the touch, often with a slight caustic quality. More rarely, the precipitation is fully fluid, jellied or solid. Solid precipitation often has qualities reminicent of frozen mud. The precipitation is most often greyish in colour, but is also frequently strangely hued, typically red, purple or blue. Its caustic qualities tends to make it prone to staining or bleaching the surfaces it lands on, and may blend its colour with that of the surface it stains.
Limbic percipitation may, unless quickly washed away by a more wholesome rain, cause vegetation to deform, or even wilt and wither. New growth on such ground is sure to be more verdant than before, but is given to aberrations.
These precipitations sometimes occur over large areas during aether storms. However, they may also be triggered by great sorceries and thaumaturgies being worked.