you have to put in salt water for 20min and then get some butter and 20 half gallons of water and get plankton at a store or fishing and let it sit for 2hr when you come back plankton should be on the alchemy make sure you get alchemy proof i did it before.
For a cockleshell: stone + plankton :)
Bacteria and water
Algae + Plankton
plankton + stone
Plankton+ stone= shell Baceria+ water= plankton
Earth and Plankton
bateria + water
Water + Plankton
earth + plankton
Plankton +Stone=cockleshell
Bacteria water
plankton and rock