Soy candle burning rate
Soy Candles have many claimed benefits. Many of these are obvious but others are more difficult to proof. There are no scientific studies comparing the properties of soy wax candles with paraffin candles, except for the one study by K. Rezaei entitled "Combustion Characteristics of Candles Made from Hydrogenated Soybean Oil".
We compared the burning rate of a soy candle with that of a paraffin candle. We do no not claim that this is a scientific study: it is just a simple experiment! We made container candles using 80 g of wax and 50 mm tea light wicks on a metal foot. The picture shows the candles (paraffin on left, soy wax on right) at different burning times. As you can see, the soy candle actually finished burning a bit earlier. However, this does not proof that the soy candles will always burn faster since the burning rate will depend also on wick size.
In our experiment, the wick size of the soy candle tended to be larger and more split than that of the paraffin candles, even after trimming the wick every two hours. Soy wax and paraffin have about the same heat of combustion, so why would soy candles burn longer? They do so probably because soy candles burn with a smaller flame. Soy wax contains larger molecules with lower volatility, which results in reduced flow of melted wax through the wick.
During this experiment, we noticed something particular. After cool down, the surface of the soy wax was convex whereas the surface of the paraffin was concave! Maybe this characteristic can be used to distinguish both types of wax!