Arcanist's Weapon of Elemental Exchange

You touch a metal weapon, transforming it into an elemental blade. Until the spell ends, that weapon deals your choice of acid, cold, fire, lightning, poison, or thunder damage, and an extra 1d6. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d6 for each slot level above 2st.