Warning: Many of these salts are toxic. Do not eat or drink them. Nickel compounds are known carcinogens.
You will need:
One or more of these: copper(II) chloride, copper sulfate, nickel sulfate, magnesium sulfate, cobalt(II) chloride, iron(II) sulfate,
Source of heat
Many metal salts form hydrates, where water molecules are incorporated in the crystal structure of the salt. The water molecules can be disconnected by heating, in most cases. The appearance of the salts can change based on their water content.
Copper(II) chloride dihydrate is green or green-blue. Heat it. It turns brown. This is the anhydrous form.
Copper sulfate pentahydrate is blue. Heat it. It turns white. This is the anhydrous form.
Nickel sulfate heptahydrate or hexahydrate is blue-green. Heat it. It turns light green. This is the anhydrous form.
Magnesium sulfate heptahydrate is colorless. Heat it. It turns white. This is the anhydrous form.
Cobalt(II) chloride hexahydrate is burgundy. Heat it. It turns blue. This is the anhydrous form.
Iron(II) sulfate heptahydrate is green. Heat it. It turns white. This is the monohydrate.
Extremely optional: Chromium(III) chloride hexahydrate is green. React it with the dangerous thionyl chloride. It will form the purple anhydrous form.