Soot formation of soy candles
We can find only one scientific study comparing the burning characteristics of soy candles with those of paraffin and beeswax candles. This study - Combustion Characteristics of Candles Made from Hydrogenated Soybean Oil - was carried out by Karamatollah Rezaei and his colleagues and published in the August 2002 issue of Journal of the American Oil Chemistsí Society.
Results of experiment by K. Rezaei
The researchers investigated following aspects of soy wax: production of soot, production of potential harmful volatile components (acrolein, formaldehyde and acetaldehyde) and burning time. The candles were made by melting 200 g of wax and poring it in glass containers in several steps to avoid cracking of the wax.
To determine the soot formation the candles were burned under a funnel and the air with sooth was then collected on a membrane filter. Disturbance of candles flame was artificially created running a fan at small speed. The amount of soot was estimated by measuring the darkness of the filter. The volatile components were captured in a trichlorophenylhydrazine solution.
They found that paraffin candles produced significant amounts of soot as opposed to soy candles, which produced little or no soot. All paraffin candles visually produced soot while burning, whereas practically no visual soot formation was observed with beeswax and soy candles. The membrane filters which collected the soot from paraffin candles showed an average L-value of 32 (rather dark) as opposed to a L-value of about 95 (very light) for both beeswax and soybean candles.Soy candles also burned slower, resulting in longer burning time. However, this effect was only observed with trimmed soy wax candles. These soy candles had a smaller flames size, which logically translates into longer burning times. The larger molecules of soy wax may explain the longer burning time: they migrate more slowly through the candlewick. The smaller flame size and lower heat production maybe advantageous in rooms where higher temperatures are not desirable. The combustion of soy wax and beeswax candles did not produce measurable quantities of formaldehyde whereas paraffin candles produced 3.2 mg formaldehyde per g paraffin. No acrolein production was observed in any of tested candles.
The study concluded that soy wax shows promise as use for production of candles. This study did not test the effects of scents on soot formation, but other studies found that the addition of scents to paraffin candles increases soot formation. Therefore, scented soy candles will likely produce more soot than unscented soy candles.
Results of own tests
We did not have the same tools as K. Rezaei. But we were able to carry out a rather simple test: we blew own out a paraffin candle and soy candle at the same time and observed the smoke formation (see picture below: left paraffin candle, right soy candle). We known, normally you are not supposed to extinguish candles by blowing them out as it may cause spillage of liquid wax and formation of unhealthy smoke. You can notice that the soy candle produces almost no smoke whereas the paraffin candle produces a lot of smoke during more than 5 seconds. You will also notice this difference in soot formation when air drafts cause the wick to flicker.