Project suitable for ages 10 and upwards.
Manufacture is simple.
Many religious statues are made of brittle porous materials which soak up liquids like a sponge. Their outside is covered by paint and glaze, so that they are effectively waterproof vessels. Red liquids look best, but remember not to use blood, because of course it coagulates. The liquid will slowly seep from the eyes for quite some time. During this time, you can collect donations from dozens of superstitious peasants.