It is vital that you burn your candle for at least 2 hours on the first burn as wax has a memory, and the size of the wax pool on the initial burn is largely the size of the wax pool from that point on. If the wax pool does not reach the edge of the glass, then 'tunneling' can occur - this is where the wax around the outside edge of the jar will never burn, leaving a 'tunnel' effect.