Strength of the seal=the strength of the magic.
also, gold, Iron, and silver seals weaken the strength of the genie even further. Lamps are hollow spaces filled made of glass used to store liquids and vapors so their air proof, in other words you don't have to put as much power into making the seal.
Did you actually think that I meant physical strength.........
Welcome one and All to the Jesters Carnival, where the prizes are greater than your wildest dreams, but the nightmares here shall silence you before you can even scream.