When you light a candle, the flame vaporizes the wax near the wick. This vaporized wax is then drawn up the wick, and the heat of the flame melts the wax near the wick. The molten wax then flows back down the wick, providing fuel for the flame to continue burning. This process is known as capillary action.
As the candle burns, the heat of the flame vaporizes the wax near the wick. This vaporized wax is then drawn up the wick, and the heat of the flame melts the wax near the wick. The molten wax then flows back down the wick, providing fuel for the flame to continue burning. This process is known as capillary action.
When the candle is extinguished, the heat of the flame is no longer present to vaporize the wax near the wick. As the wax cools, it begins to solidify. The solidified wax then forms a seal around the wick, trapping any unburned vaporized wax inside the jar. Over time, this trapped wax will begin to turn black.