A candle wick is not 'just a piece of string', but is a design engineering feat in itself.
There are many factors that are involved in the efficient burning of a candle apart from wax type and purity... The wick has many properties that affect the way the finished candle performs. It needs to be naturally absorbent or it needs to have a strong capillary action between non absorbent fibres so that melted wax is sucked up further into the hotter part of the flame where it can be vapourised and thus burn.
Two distinct type of braiding are used... Plaited and square braiding.
The plaited wicks are made of three strands each of which consists of several yarns.
The braided version usually has four strands (two of which usually contain more individual yarns than the other two). The uneven structure enables the burned wick to curl over to such an extent that it pierces the outer shell of the flame. The extra oxygen in this area allows the carbon to be converted to gaseous carbon dioxide and thus the wick is automatically trimmed. Braided wicks are usually used in the making of beeswax candles.
The fibre type, amount of twist and diameter all have independent effects.
Impregnations and Treatments
Various dressings can be applied to alter the degree of wax penetration or capillary action within and between strands.
The size and type of wick that is most suitable for a given candle is a factor that is often ignored or left to chance.