This whetstone has 1d4 + 1 charges.  With at least 10 minutes of work, you can expend 1 charge to upgrade a weapon.  The weapon immediately becomes a weapon + 1.  The weapon also deals an extra 1d4 damage on a hit.  The damage type is force, radiant, or any type of elemental damage, as determined by the DM.   This whetstone is consumable.  Once all the charges are expended, the item becomes a nonmagical whetstone.