Wash the mortar and pestle with warm water and a stiff brush
Do not use soap unless the manufacturer specifically allows it
Rinse thoroughly and let it dry completely
Grind a handful of uncooked white rice into a fine powder
Discard the rice powder
Repeat with fresh rice until the powder stays mostly white
Wipe out the mortar and pestle with a dry cloth
For porous stone, repeat the rice grinding process several times if needed
For stubborn residue, grind coarse salt with a little water
Rinse and dry completely after seasoning
Avoid seasoning methods not recommended for the material of your mortar and pestle