Acid is a liquid that hurts any character that steps on it, though this can be mitigated with acid resistance. It will evaporate into Corrosive Gas above temperature 350.
Standing in acid deals up to 3d2 damage. Less pure acid rolls less dice of damage - the actual number is (acid% / 30)d2, with fractions rounded down. Drinking it instead deals up to 10d10 damage. Player with Bilge Sphincter will gain full 100% Acid Resistance and the ability to spit from a pool full of acid
Acid dissolves items placed in it. If acid is poured on a creature, there is a chance that any armor the creature is wearing will be melted.
Acid can be also used in making recipes for acid and corrosion related effects.
It can be found in Golgotha and Bethesda Susa and is also used as a projectile by Spitting Slugs (who also produce a large pool of acid on death). Some Sludge in Rainbow wood has a chance to be made as an acid sludge.
You can only store acid in the following:
It will melt other container that are inherently organic such as waterskins.