Thanks all. The variable I came up with is size/shape. I chose it so that I can test whether different shapes/size will help it burn faster or make it slower.
BTW. I'm going to go buy some candles now. So far I bought those small circular thinnish candles. Bought white, blue, and red of those. Then today, I'm going to buy those big squarish candles, same color. Then I'm buying normal candles.
Is that good? Then I'm going to light them on a candle holding cup. Measure the changed mass every 30 minutes or 1 hour while subtracting the cup mass. I'm going to graph those until the candles are all melted. Then I'm going to paste it on my display board.
Is that good?