Re: Do wax candles burn at different rates because of dyes?

Dear Lisa,

That is an interesting project and you are correct in your observation that 
different color candles burn at different rates. It IS because of the dye, but 
not for the reason you may think. Dyes in candles [we're talking about solid 
color candles] only comprise a very small fraction of the overall weight [1% or 
less] and are not likely to be the contributing cause all by themself.

Fire needs three things to propagate: fuel, heat and air. Remove any one and 
the fire stops; increase any one and the fire burns more vigorously.

Let's take the example of a white and a black candle, of equal size and wax 
type. When the white candle burns, it is hot [of course!] and some of this heat 
is used to melt the next lower layer of wax. White is "white" because it 
reflects a lot of light back to our eyes. Well, it also reflects heat very well 
and if the heat is reflected away, there isn't as much heat left to melt the 
next layer of fuel.

Black is "black" because it absorbs light instead of reflecting it. It also 
absorbs more heat which leads to the wax melting faster which means more fuel 
for the fire and it burns faster.

Another way to think of this is to imagine two cars [the same] with full gas 
tanks. One is driven at 35 mph and the other driver 'gives it the gas' and 
drives at 70 mph. Which car will run out of gas first? It's the same thing with 
the candles, the more fuel they are given, the faster they burn.

The shape of the candle and its wax composition [waxes have different melting 
points, so will contribute fuel at different rates] will also influence burning 
rates

Consider two 100 gram white candles: one is shaped like a flat pancake 6 inches 
in diameter and the other one is as skinny as a soda straw and a yard long. 
Light them at the same time. Which do you think will burn up completely? Which 
will go out first? Think about it, formulate a hypothesis {prediction] and then 
test it experimentally. That is what science is all about!

Good luck

Ken Johnsen